Risks of Myclobutanil Use to Federally 

Threatened California Red-legged Frog 

(Rana aurora draytonii) 

Pesticide Effects Determination 

Environmental Fate and Effects Division 

Office of Pesticide Programs 

Washington, D.C. 20460 

June 17, 2009 
Primary Authors: 

James K. Wolf, Ph.D., Environmental Scientist 

Michael Lowit, Ph.D., Ecologist 

Rebecca Daiss, M.S., Biologist 

Secondary Review: 

Pamela M. Hurley, Ph.D., Toxicologist 

James Hetrick, Ph.D., Senior Science Advisor 

Branch Chief, Environmental Risk Assessment Branch 3: 

Dana Spatz 

2
Table of Contents 

1 Executive Summary.......................................................................................... 10 

2 Problem Formulation ........................................................................................ 17 

2.1 Purpose.............................................................................................................. 17 

2.2 Scope................................................................................................................. 19 

2.3 Previous Assessments....................................................................................... 20 

2.4 Stressor Source and Distribution ...................................................................... 21 

2.4.1 Physical and Chemical Properties................................................................. 21 

2.4.2 Environmental Fate Assessment................................................................... 22 

2.4.3 Environmental Transport Assessment .......................................................... 25 

2.4.4 Mechanism of Action.................................................................................... 25 

2.4.5 Use Characterization..................................................................................... 26 

2.5 Assessed Species............................................................................................... 30 

2.5.1 Distribution ................................................................................................... 30 

2.5.2 Reproduction................................................................................................. 33 

2.5.3 Diet................................................................................................................ 34 

2.5.4 Habitat........................................................................................................... 34 

2.6 Designated Critical Habitat............................................................................... 35 

2.7 Action Area....................................................................................................... 37 

2.8 Assessment Endpoints and Measures of Ecological Effect.............................. 40 

2.8.1 Assessment Endpoints for the CRLF............................................................ 40 

2.8.2 Assessment Endpoints for Designated Critical Habitat................................ 42 

2.9 Conceptual Model............................................................................................. 44 

2.9.1 Risk Hypotheses............................................................................................ 44 

2.9.2 Diagram......................................................................................................... 44 

2.10 Analysis Plan .................................................................................................... 46 

2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model............. 47 

3 Exposure Assessment ....................................................................................... 51 

3.1 Label Application Rates and Intervals.............................................................. 51 

3.2 Aquatic Exposure Assessment.......................................................................... 52 

3.2.1 Modeling Approach ...................................................................................... 52 

3.2.2 PRZM Scenarios........................................................................................... 53 

3.2.3 Model Inputs................................................................................................. 56 

3.2.4 Available Monitoring Data ........................................................................... 58 

3.2.5 Modeling Results.......................................................................................... 60 

3.3 Terrestrial Animal Exposure Assessment......................................................... 64 

3.4 Terrestrial Plant Exposure Assessment............................................................. 67 

4 Effects Assessment ........................................................................................... 68 

4.1 Evaluation of Aquatic Ecotoxicity Studies....................................................... 71 

4.1.1 Toxicity to Freshwater Fish .......................................................................... 72 

4.1.2 Toxicity to Freshwater Invertebrates............................................................ 73 

4.1.3 Toxicity to Aquatic Plants ............................................................................ 76 

4.2 Toxicity of Myclobutanil to Terrestrial Organisms.......................................... 77 

4.2.1 Toxicity to Birds........................................................................................... 78 

4.2.2 Toxicity to Mammals.................................................................................... 81 

3
4.2.3 Toxicity to Terrestrial Invertebrates ............................................................. 87 

4.2.4 Toxicity to Terrestrial Plants ........................................................................ 87 

4.3 Use of Probit Slope Response Relationship to Provide Information on the 

Endangered Species Levels of Concern............................................................ 89 

4.4 Incident Database Review ................................................................................ 90 

4.4.1 Terrestrial Incidents...................................................................................... 90 

4.4.2 Aquatic Incidents.......................................................................................... 91 

5 Risk Characterization........................................................................................ 91 

5.1 Risk Estimation................................................................................................. 91 

5.1.1 Exposures in the Aquatic Habitat ................................................................. 91 

5.1.2 Exposures in the Terrestrial Habitat ............................................................. 94 

5.1.3 Primary Constituent Elements of Designated Critical Habitat ..................... 99 

5.2 Risk Description ............................................................................................. 101 

5.2.1 Direct Effects.............................................................................................. 105 

5.2.2 Indirect Effects (via Reductions in Prey Base)........................................... 108 

5.2.3 Indirect Effects (via Habitat Effects).......................................................... 112 

5.2.4 Effects to Designated Critical Habitat ........................................................ 114 

5.2.5 Spatial Extent of Potential Effects.............................................................. 117 

6 Uncertainties................................................................................................... 121 

6.1 Exposure Assessment Uncertainties............................................................... 121 

6.1.1 Maximum Use Scenario.............................................................................. 121 

6.1.2 Aquatic Exposure Modeling of Myclobutanil ............................................ 121 

6.1.3 Usage Uncertainties.................................................................................... 123 

6.1.4 Terrestrial Exposure Modeling of Myclobutanil ........................................ 123 

6.1.5 Spray Drift Modeling.................................................................................. 124 

6.2 Effects Assessment Uncertainties................................................................... 125 

6.2.1 Age Class and Sensitivity of Effects Thresholds........................................ 125 

6.2.2 Use of Surrogate Species Effects Data ....................................................... 125 

6.2.3 Sublethal Effects......................................................................................... 125 

6.2.4 Location of Wildlife Species....................................................................... 126 

6.2.5 Use of Surrogate Chemical Effects Data .................................................... 126 

7 Risk Conclusions ............................................................................................ 126 

8 References....................................................................................................... 132 

4
List of Tables 

Table 1.1 Effects Determination Summary for Myclobutanil Use and the CRLF ........... 13 

Table 1.2 Effects Determination Summary for Myclobutanil Use and CRLF Critical 

Habitat Impact Analysis.................................................................................. 14 

Table 1.3 Myclobutanil Use-specific Direct Effects Determinations1 for the CRLF....... 15 

Table 1.4 Myclobutanil Use-specific Indirect Effects Determinations1

 Based on Effects to 

Prey ................................................................................................................. 16 

Table 2.1 Summary of Myclobutanil and 1,2,4-triazole Physical and Environmental Fate 

Properties........................................................................................................ 23 

Table 2.2 Myclobutanil Uses Assessed for the CRLF..................................................... 26 

Table 2.3 Summary of California Department of Pesticide Registration (CDPR) Pesticide 

Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered 

Myclobutanil Uses.......................................................................................... 29 

Table 2.4 Assessment Endpoints and Measures of Ecological Effects ........................... 41 

Table 2.5 Summary of Assessment Endpoints and Measures of Ecological Effect for 

Primary Constituent Elements of Designated Critical Habitata

...................... 43 

Table 3.1 Summary of PRZM and EXAMS Environmental Fate Data Used for Aquatic 

Exposure Inputs for Myclobutanil and Myclobutanil plus 1,2,4-triazole for 

Endangered Species Assessment for the CRLF 1 ........................................... 57 

Table 3.2 Myclobutanil results from the summary of analysis of moderate-use pesticides 

and degradates in water samples from water supply intakes and finishedsupply taps in Reservoir Pilot Monitoring Program. (USGS, 2001) .............. 58 

Table 3.3 Distribution of Myclobutanil Concentrations (μg/L) in USGS NAWQA Surface 

Water Monitoring Data Monitoring Data (1998-2007) ................................. 59 

Table 3.4 Myclobutanil concentrations in Rain in California Agricultural Watershed 

(Vogel et al., 2008) ......................................................................................... 59 

Table 3.5 Aquatic EECs (μg/L) for Myclobutanil Uses in California.............................. 60 

Table 3.6 EECs California Red legged frog – myclobutanil + 1,2,4-triazole................... 61 

Table 3.7 Time (years) for myclobutanil and myclobutanil plus 1,2,4-triazole to reach 

plateau concentration in standard farm pond (USEPA, 2007)........................ 64 

Table 3.8 Input Parameters for Foliar Applications Used to Derive Terrestrial EECs for 

myclobutanil with T-REX............................................................................... 65 

Table 3.9 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based 

Exposures of the CRLF and its Prey to Myclobutanil .................................... 66 

5
Table 3.10 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via Effects to 

Terrestrial Invertebrate Prey Items ................................................................. 67 

Table 3.11 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and Semiaquatic Areas Exposed to Myclobutanil via Runoff and Drift ....................... 68 

Table 4.1 Freshwater Aquatic Toxicity Profile for Myclobutanil .................................... 71 

Table 4.2 Categories of Acute Toxicity for Fish and Aquatic Invertebrates.................... 72 

Table 4.3 Conazole (DMI triazole) Fungicide Chronic Toxicity to Aquatic Invertebrates

......................................................................................................................... 75 

Table 4.4 Conazole (DMI Triazole) Fungicide Toxicity to Aquatic Vascular Plants..... 76 

Table 4.5 Terrestrial Toxicity Profile for Myclobutanil ................................................... 77 

Table 4.6 Categories of Acute Toxicity for Avian and Mammalian Studies.................... 78 

Table 4.7 Avian Acute Toxicity Data ............................................................................... 79 

Table 4.8 Avian Chronic Toxicity Data............................................................................ 81 

Table 4.9 Mammalian Acute Toxicity Data ..................................................................... 82 

Table 4.10 Acute Rat Toxicity Comparison of Myclobutanil Formulations.................... 83 

Table 4.11 Mammalian Chronic Toxicity Data ................................................................ 85 

Table 4.12 Terrestrial Plant Toxicity Data for 5 Other DMI Fungicides......................... 88 

Table 5.1 Summary of Acute and Chronic Direct Effect RQs for the Aquatic-phase CRLF

......................................................................................................................... 92 

Table 5.2 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to the 

CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items (prey 

of CRLF juveniles and adults in aquatic habitats).......................................... 94 

Table 5.3 Summary of Acute RQs Used to Estimate Direct Effects to the Terrestrialphase CRLF (non-granular application) ......................................................... 95 

Table 5.4 Summary of Acute RQs Used to Estimate Direct Effects to the Terrestrialphase CRLF (granular application)................................................................. 96 

Table 5.5 Summary of Chronic RQs Used to Estimate Direct Effects to the Terrestrialphase CRLF (non-granular application) ......................................................... 96 

Table 5.6 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to the 

Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary 

Food Items (non-granular application) ........................................................... 98 

Table 5.7 Summary of Acute RQs Used to Estimate Indirect Effects to the Terrestrialphase CRLF via Direct Effects on Small Mammals as Dietary Food Items 

(granular application)...................................................................................... 98 

Table 5.8 Risk Estimation Summary for Myclobutanil - Direct and Indirect Effects to 

CRLF............................................................................................................. 102 

6
Table 5.9 Risk Estimation Summary for Myclobutanil – PCEs of Designated Critical 

Habitat for the CRLF .................................................................................... 103 

Table 5.10 Thirty Seven Gram Amphibian T-HERPS RQs for Consumption of Small 

Herbivorous Mammals.................................................................................. 106 

Table 5.11 Myclobutanil Application Rates Combined with Endpoints from 5 Triazole 

DMI Fungicides Exceeding the Terrestrial Plant LOC for Listed and NonListed Dicots in Semi-Aquatic Areas ........................................................... 114 

Table 5.12 Input Parameters for Simulation of Myclobutanil in Spray Drift Using AgDrift 

(v. 2.01)......................................................................................................... 118 

Table 5.13 Summary of Maximum Predicted Distances for Potential Spray Drift Effects

....................................................................................................................... 118 

Table 7.1 Effects Determination Summary for Myclobutanil Use and the CRLF ........ 128 

Table 7.2 Effects Determination Summary for Myclobutanil Use and CRLF Critical 

Habitat Impact Analysis................................................................................ 129 

7
List of Figures 

Figure 2.1 Myclobutanil Degradates................................................................................. 24 

Figure 2.2 Myclobutanil Terrestrial Plant Metabolite ...................................................... 24 

Figure 2.3 Map of Estimated Annual Agricultural Use of Myclobutanil in 2002............ 28 

Figure 2.4 Recovery Unit, Core Area, Critical Habitat and Occurrence Designations for 

CRLF............................................................................................................... 32 

Figure 2.5 CRLF Reproductive Events by Month............................................................ 33 

Figure 2.6 Initial Area of Concern of “footprint” of potential use for myclobutanil........ 39 

Figure 2.7 Conceptual Model for Myclobutanil Effects on Terrestrial Phase of the CRLF

......................................................................................................................... 45 

Figure 2.8 Conceptual Model for Myclobutanil Effects on Aquatic Phase of the CRLF 46 

Figure 3.1 Summary of Applications (pounds versus date) of Myclobutanil to Grapes in 

2001 from CDPR PUR Data........................................................................... 53 

Figure 3.2 Accumulation of PRZM/EXAMS Annual Peak Concentrations of 

Myclobutanil and Myclobutanil plus 1,2,4-triazole in the California Tomato 

Scenario (surrogate for CA Okra aerial spray use)......................................... 63 

Figure 5.1 Overlap Map: CRLF Habitat and Myclobutanil Initial Area of Concern .... 120 

8
Appendices 

Appendix A Multi-ai Product Analysis 

Appendix B Aquatic Exposure Modeling 

Appendix C Environmental Fate Data 

Appendix D BEAD Analysis of CDPR PUR Database 

Appendix E CRLF – Spatial Summary 

Appendix F The Risk Quotient Method and Levels of Concern 

Appendix G T-REX Example Output 

Appendix H Bibliography of ECOTOX Open Literature 

Appendix I Accepted ECOTOX Data Table 

Appendix J HED Effects Table 

Appendix K Ecotoxicity Data 

Appendix L Incident Data 

Appendix M T-HERPS Example Output 

Appendix N Terrplant Example Output 

Appendix O Ecotoxicity and Environmental Fate Bibliography 

Attachment 1. Status and Life History of the California Red-legged Frog 

Attachment 2. Baseline Status and Cumulative Effects for the California Red-legged Frog 

9
1 Executive Summary 

The purpose of this assessment is to evaluate potential direct and indirect effects on the 

California red-legged frog (Rana aurora draytonii) (CRLF) arising from FIFRA 

regulatory actions regarding use of myclobutanil on agricultural and non-agricultural 

sites. In addition, this assessment evaluates whether these actions can be expected to 

result in effects to the species’ designated critical habitat. This assessment was 

completed in accordance with the U.S. Fish and Wildlife Service (USFWS) and National 

Marine Fisheries Service (NMFS) Endangered Species Consultation Handbook

(USFWS/NMFS, 1998 and procedures outlined in the Agency’s Overview Document 

(U.S. EPA, 2004). 

The CRLF was listed as a threatened species by USFWS in 1996. The species is endemic 

to California and Baja California (Mexico) and inhabits both coastal and interior 

mountain ranges. A total of 243 streams or drainages are believed to be currently 

occupied by the species, with the greatest numbers in Monterey, San Luis Obispo, and 

Santa Barbara counties (USFWS, 1996) in California. 

Myclobutanil is a systemic fungicide. Current labeled uses of myclobutanil include the 

following food uses: almond, apple, apricot, artichoke, asparagus, beans (succulent), 

blackberry, boysenberry, canistel, cherry, chrysanthemum garland, cotton, cucurbits 

(pumpkin, squash, watermelon), currant, dewberry, eggplant, gooseberry, grapes, hops, 

lettuce (head, leaf), loganberry, mamey (mamme apple), mango, mayhaw (Hawthorn), 

melons, nectarines, okra, olallie berries, papaya, peach, pepper, peppermint, pimento, 

plum, prune, raspberry (black, red), sapodilla, sapote white, spearmint, star apple, 

strawberry, tomato, and youngberry. Non-food/non-feed uses include bluegrass, 

commercial/industrial lawns, cotton (seed), Douglas Fir (seed orchard, shelter belt), golf 

course turf, grasses grown for seed, hybrid cottonwood/poplar plantations, loblolly pine 

(forest), ornamental and shade trees, ornamentals (ground cover, herbaceous plants, 

lawns and turf, non-flowering plants, sod farm (turf), woody shrubs and vines), 

residential lawns and slash pine forest. Grapes, apples, almonds, and cherries together 

make up 80% of all labeled uses of myclobutanil in California. 

Myclobutanil is stable to both hydrolysis and photolysis. Myclobutanil degradation is 

controlled by microbial-mediated transformations. Myclobutanil is moderately persistent 

to persistent (DT50 > 70 days) in aerobic soils and persistent in anaerobic soils. The major 

degradation products observed in the aerobic soil metabolism (ASM) studies are 1,2,4-

triazole (maximum 18%), CO2, a polar degradate (β-4-chlorophenyl-β-cyano-γ-(1H1,2,4-triazole)-butyric acid and unextractable residues. At the conclusion of the 367 day 

aerobic soil metabolism study, 29 to 33 percent of the applied radioactivity remained as 

parent myclobutanil and 13 percent was identified as 1,2,4-triazole. Once the maximum 

level of 1,2,4-triazole is reached, its decline pattern parallels myclobutanil. Terrestrial 

field dissipation half-life values range from 92 to 292 days. Because the myclobutanil 

residues are fairly persistent, the potential to remain in soil is possible, especially when 

10
there are multiple applications. Fate studies for 1,2,4-triazole suggest aerobic soil 

metabolism half-lives ranging from 22 to 375 days. 

In addition to 1,2,4-triazole, plant and animal metabolism studies have identified a 

number of metabolites not identified in the environmental fate studies (soil and water). 

These metabolites include triazole alanine (TA), triazole acetic acid (TAA) and RH-9090. 

Myclobutanil is mobile as indicated by the Freundlich Kads values (from 1.46 to 9.77 

mL/g). The degradate (1,2,4-triazole) has lower Freundlich Kads values (0.234 to 0.833 

mL/g), suggesting it would be more mobile than the parent compound. 

Due to its persistence and mobility, the primary routes of dissipation are thought to be 

through leaching, runoff, and spray drift. The limited monitoring data for myclobutanil 

shows detected myclobutanil residues in surface water in California, but not in ground 

water. Myclobutanil was also found in rainwater in a California watershed, suggesting the 

occurrence of atmospheric transport. 

Since CRLFs exist within aquatic and terrestrial habitats, exposure of the CRLF, its prey 

and its habitats to myclobutanil are assessed separately for the two habitats. Tier-II 

aquatic exposure models are used to estimate high-end exposures of myclobutanil in 

aquatic habitats resulting from runoff and spray drift from different uses. The aquatic 

assessment quantitatively considers exposure from parent myclobutanil as well as 

exposure from myclobutanil and the degradation product 1,2,4-triazole. 1,2,4-triazole is a 

major degradation product that is slowly formed from biodegradation under aerobic and 

anaerobic conditions in soil. The 1,2,4-triazole’s persistence appears to be equal to or 

less than that of the parent myclobutanil, and it is more mobile. Peak model-estimated 

environmental concentrations in surface water resulting from different myclobutanil uses 

range from 2.1 to 61.4 μg/L. These estimates are supplemented with analysis of available 

California surface water monitoring data from U. S. Geological Survey’s National Water 

Quality Assessment (NAWQA) program and the California Department of Pesticide 

Regulation. The maximum concentration of parent myclobutanil reported by NAWQA 

for California surface waters with agricultural watersheds is 0.51 μg/L. This value is 

approximately 120 times less than the maximum model-estimated environmental 

concentration. There were no detections of myclobutanil reported in the California 

Department of Pesticide Regulation surface water database. 

To estimate myclobutanil exposures to the terrestrial-phase CRLF, and its potential prey 

resulting from uses involving myclobutanil applications, the T-REX model is used for 

foliar, granular and cotton seed treatment uses. The AgDRIFT model is also used to 

estimate deposition of myclobutanil on terrestrial and aquatic habitats from spray drift. 

Due to lack of terrestrial plant data for myclobutanil, the TerrPlant model is used for risk 

description purposes using plant effects data from similar fungicides to estimate 

myclobutanil exposures to terrestrial-phase CRLF habitat, including plants inhabiting 

semi-aquatic and dry areas, resulting from uses involving foliar myclobutanil 

applications. The T-HERPS model is used to allow for further refinement of oral 

exposures of terrestrial-phase CRLFs (the model allows for an estimation of food intake 

11
for poikilotherms using the same basic procedure as T-REX to estimate avian food 

intake). 

 

The effects determination assessment endpoints for the CRLF include direct toxic effects 

on the survival, reproduction, and growth of the CRLF itself, as well as indirect effects, 

such as reduction of the prey base or potential effects to its critical habitat. Direct effects 

to the CRLF in the aquatic habitat are based on toxicity information for freshwater fish, 

which are generally used as a surrogate for aquatic-phase amphibians. In the terrestrial 

habitat, direct effects are based on toxicity information for birds, which are used as a 

surrogate for terrestrial-phase amphibians. Given that the CRLF’s prey items and 

designated critical habitat requirements in the aquatic habitat are dependant on the 

availability of freshwater aquatic invertebrates and aquatic plants, toxicity information 

for these taxonomic groups is also discussed. In the terrestrial habitat, indirect effects 

due to depletion of prey are assessed by considering effects to terrestrial insects, small 

terrestrial mammals, and frogs. Indirect effects due to effects to the terrestrial habitat are 

characterized by available data for terrestrial monocots and dicots. 

One of the myclobutanil degradation products observed in environmental fate studies is 

1,2,4-triazole. The Office of Pesticide Program’s Health Effects Division (HED) has 

conducted aggregate human health risk assessments for 1,2,4-triazole and triazole 

conjugates (triazole alanine and triazole acetic acid) derived from conazole fungicides 

(USEPA. 2006a, 2006b). 1,2,4-triazole and its conjugates are common metabolites to the 

class of compounds known as the triazoles (a.k.a. triazole-derivative fungicides, T-D 

fungicides, conazoles). These compounds all have a triazole ring with nitrogen atoms at 

the 1, 2, and 4 positions. 

For the terrestrial exposure assessment, a conservative default foliar dissipation half-life 

of 35 days is used for all uses of myclobutanil to account for terrestrial exposure to the 

parent, the primary plant metabolite RH-9090, the 1,2,4-triazole degradate and the 

triazole conjugates (triazole alanine and triazole acetic acid). Mammalian toxicity data 

on the degradates and/or a structure-activity analysis on degradates with no toxicity data 

indicate that they are either equivalent to or less toxic than the parent. 

Risk quotients (RQs) are derived as quantitative estimates of potential high-end risk. 

Acute and chronic RQs are compared to the Agency’s levels of concern (LOCs) to 

identify instances where myclobutanil use within the action area has the potential to 

adversely affect the CRLF and its designated critical habitat via direct toxicity or 

indirectly based on direct effects to its food supply (i.e., freshwater invertebrates, algae, 

fish, frogs, terrestrial invertebrates, and mammals) or habitat (i.e., aquatic plants and 

terrestrial upland and riparian vegetation). When RQs for each particular type of effect 

are below LOCs, the pesticide is determined to have “no effect” on the CRLF. Where 

RQs exceed LOCs, a potential to cause adverse effects is identified, leading to a 

conclusion of “may affect.” If a determination is made that use of myclobutanil use 

within the action area “may affect” the CRLF or its designated critical habitat, additional 

information is considered to refine the potential for exposure and effects, and the best 

available information is used to distinguish those actions that “may affect, but are not 

12
likely to adversely affect” (NLAA) from those actions that are “likely to adversely affect” 

(LAA) the CRLF. 

Based on the best available information, the Agency makes a “Likely to Adversely 

Affect” determination for the CRLF from the use of myclobutanil. Additionally, the 

Agency has determined that there is the potential for effects to CRLF designated critical 

habitat from the use of the chemical. The CRLF and/or its critical habitat may be affected 

for all crops, cotton and turf uses. The terrestrial-phase CRLF may be at risk following 

consumption of small herbivorous mammals (acute exposure: most crop uses, cotton and 

turf) and small insects (chronic exposure: cotton and turf uses). Direct effects on the 

aquatic-phase CRLF are not expected. Indirect effects to the terrestrial-phase CRLF, 

based on reduction in prey base may occur with terrestrial phase amphibians following 

acute exposure (most crops, cotton and turf) and chronic exposure (turf and cotton) and 

with mammals following acute exposure (apple, apricot, cherry, nectarine, peach, hops 

and turf uses) and chronic exposure (all uses). Indirect effects to the aquatic-phase 

CRLF, based on reduction in prey base are not expected. Indirect effects to both the 

aquatic- and terrestrial-phase CRLF based on aquatic and riparian habitat, cover and/or 

primary productivity may occur due to potential effects on the riparian terrestrial plant 

community, particularly dicots in semi-aquatic areas (all uses). Direct effects on aquatic 

plant habitat are not expected. Based on potential effects to the avian/terrestrial-phase 

amphibians, mammals and terrestrial plants, there is a potential for terrestrial and aquatic 

habitat effects. A summary of the risk conclusions and effects determinations for the 

CRLF and its critical habitat is presented in Table 1.1 and 1.2. Further information on 

the results of the effects determination is included as part of the Risk Description in 

Section 5.2. Given the LAA determination for the CRLF and potential effects to 

designated critical habitat, a description of the baseline status and cumulative effects for 

the CRLF is provided in Attachment 2. 

Table 1.1 Effects Determination Summary for Myclobutanil Use and the CRLF 

Assessment 

Endpoint 

Effects 

Determination 1

Basis for Determination 

Potential for Direct Effects

Aquatic-phase (Eggs, Larvae, and Adults): 

Acute and chronic freshwater fish RQs are below the respective level of concern 

(LOC) for all uses of myclobutanil. 

Terrestrial-phase (Juveniles and Adults): 

The acute avian LOC is exceeded at application rates of 0.12 lb a.i./A and above 

(most crops, cotton and turf). The highest probabilities of an individual effect 

range from 1 in ~ 3.88E+02 to 1 in ~ 1. The chronic avian LOC is exceeded 

following uses on cotton (0.06 lb a.i./cwt) and turf at 1.3 lbs a.i./A. Myclobutanil 

uses overlap CRLF habitat. 

Potential for Indirect Effects

Survival, growth, 

and/or reproduction 

of CRLF 

individuals 

LAA1

Aquatic prey items, aquatic habitat, cover and/or primary productivity 

Acute and chronic freshwater fish RQs are below the respective LOC for all uses 

13
Assessment 

Endpoint 

Effects Basis for Determination 

Determination 1

of myclobutanil. 

Acute freshwater invertebrate RQs are below the LOC for all uses of 

myclobutanil. No chronic freshwater invertebrate studies are available for 

myclobutanil. Weight of the evidence from RQs based on myclobutanil EECs 

and toxicity data from 9 other conazole fungicides indicates that minimal impact 

is expected from chronic exposure to freshwater invertebrates as prey items. 

Acute RQs for aquatic non-vascular plants for all uses of myclobutanil are below 

the LOC. No aquatic vascular plant studies are available. Weight of the 

evidence from RQs based on myclobutanil EECs and toxicity data from 7 other 

conazole fungicides indicates minimal impact to the CRLF aquatic habitat, cover 

and/or primary productivity. 

Terrestrial prey items, riparian habitat 

See description above for direct effects on birds as surrogate for terrestrial phase 

amphibians. LOCs for listed mammals exceeded following acute exposure at 

application rates of 0.25 lb a.i./A and above and chronic exposure at application 

rates of 0.0625 lbs a.i./A and above. Percent effect on mammalian population is 

estimated to range from 4 – 42% for the myclobutanil uses. Myclobutanil uses 

overlap CRLF habitat. 

For terrestrial invertebrates, the honeybee acute contact data show no mortalities 

at concentration levels up to and including 2836 ppm (highest level tested), 

which is higher than highest dietary-based EEC for small insects with the use on 

turf; however, there is some uncertainty for potential mortality. For large 

invertebrates, there is no concern. Based on the results of the honey bee study 

and weight of the evidence from open literature studies, indirect impact to the 

CRLF via effects of myclobutanil on terrestrial invertebrate food items is 

expected to be minimal. 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 1

 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely 

affect (LAA)

Table 1.2 Effects Determination Summary for Myclobutanil Use and CRLF Critical 

Habitat Impact Analysis 

Assessment 

Endpoint 

Effects 

Determination 

Basis for Determination 

Modification of 

aquatic-phase PCE Habitat Effects 

Acute RQs for aquatic non-vascular plants for all uses of myclobutanil are below 

the LOC. 

No aquatic vascular plant studies are available. Weight of the evidence from 

RQs based on myclobutanil EECs and toxicity data from 7 other conazole 

fungicides indicates minimal impact to the CRLF aquatic habitat. 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

14
Assessment 

Endpoint 

Effects Basis for Determination 

Determination 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 

Acute and chronic freshwater fish RQs are below the respective levels of concern 

(LOC) for all uses of myclobutanil. 

Indirect effects to the CRLF through effects to its prey in the aquatic habitat 

(freshwater invertebrates) are expected to be minimal (see table 1.1). 

Modification of 

terrestrial-phase 

PCE 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 

The acute avian LOC is exceeded at application rates of 0.12 lb a.i./A and above 

(most crops, cotton and turf). The chronic avian LOC is exceeded following uses 

on cotton (0.06 lb a.i./cwt) and turf at 1.3 lbs a.i./A. 

LOCs for endangered species exceeded following acute exposure on a dose-basis 

for many crops and chronic exposure on a dose-basis for all uses and on a 

dietary-basis for many crops. 

For terrestrial invertebrates, the weight of the evidence indicates that minimal 

potential indirect impact to the CRLF via effects on terrestrial invertebrate food 

items is expected. 

Table 1.3 Myclobutanil Use-specific Direct Effects Determinations1

 for the CRLF 

Aquatic Habitat Terrestrial Habitat Use(s) Acute Chronic Acute Chronic 

All uses NE NE - - 

All uses except artichoke, boysenberry, dewberry, 

youngberry, grape and tomato - - LAA - 

Artichoke, boysenberry, dewberry, youngberry, grape 

and tomato - - NE - 

Cotton and turf - - - LAA 

All uses except cotton and turf - - - NE 1 NE = No effect; NLAA = May affect, but not likely to adversely affect; LAA = Likely to adversely affect 

15
Table 1.4 Myclobutanil Use-specific Indirect Effects Determinations1

 Based on 

Effects to Prey 

Aquatic 

Invertebrates 

Aquatic-phase 

frogs and fish 

Terrestrialphase frogs Small Mammals 

Use(s) Algae 

Acute Chronic 

Terrestrial 

Invertebrates 

(Acute) Acute Chronic Acute Chronic Acute Chronic 

All uses NE NE NLAA NLAA NE NE - - - LAA 

Footnote 2 - - - - - - LAA - - - 

Cotton, turf - - - - - - - LAA - - 

Footnote 3 - - - - - - - - LAA - 

1 NE = No effect; NLAA = May affect, not likely to adversely affect; LAA = Likely to adversely affect 

2 All uses except artichoke, boysenberry, dewberry, youngberry, grape and tomato 

3 Apple, apricot, cherry, nectarine, peach, hops and turf uses 

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish 

and Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

When evaluating the significance of this risk assessment’s direct/indirect and habitat 

effects determinations, it is important to note that pesticide exposures and predicted risks 

to the species and its resources (i.e., food and habitat) are not expected to be uniform 

across the action area. In fact, given the assumptions of drift and downstream transport 

(i.e., attenuation with distance), pesticide exposure and associated risks to the species and 

its resources are expected to decrease with increasing distance away from the treated field 

or site of application. Evaluation of the implication of this non-uniform distribution of 

risk to the species would require information and assessment techniques that are not 

currently available. Examples of such information and methodology required for this 

type of analysis would include the following: 

• Enhanced information on the density and distribution of CRLF life stages 

within specific recovery units and/or designated critical habitat within the 

action area. This information would allow for quantitative extrapolation 

of the present risk assessment’s predictions of individual effects to the 

proportion of the population extant within geographical areas where those 

effects are predicted. Furthermore, such population information would 

allow for a more comprehensive evaluation of the significance of potential 

resource impairment to individuals of the species. 

• Quantitative information on prey base requirements for individual aquaticand terrestrial-phase frogs. While existing information provides a 

preliminary picture of the types of food sources utilized by the frog, it 

does not establish minimal requirements to sustain healthy individuals at 

varying life stages. Such information could be used to establish 

biologically relevant thresholds of effects on the prey base, and ultimately 

establish geographical limits to those effects. This information could be 

used together with the density data discussed above to characterize the 

likelihood of adverse effects to individuals. 

• Information on population responses of prey base organisms to the 

pesticide. Currently, methodologies are limited to predicting exposures 

16
and likely levels of direct mortality, growth or reproductive impairment 

immediately following exposure to the pesticide. The degree to which 

repeated exposure events and the inherent demographic characteristics of 

the prey population play into the extent to which prey resources may 

recover is not predictable. An enhanced understanding of long-term prey 

responses to pesticide exposure would allow for a more refined 

determination of the magnitude and duration of resource impairment, and 

together with the information described above, a more complete prediction 

of effects to individual frogs and potential effects to critical habitat. 

2 Problem Formulation 

Problem formulation provides a strategic framework for the risk assessment. By 

identifying the important components of the problem, it focuses the assessment on the 

most relevant life history stages, habitat components, chemical properties, exposure 

routes, and endpoints. The structure of this risk assessment is based on guidance 

contained in U.S. EPA’s Guidance for Ecological Risk Assessment (U.S. EPA 1998), the 

Services’ Endangered Species Consultation Handbook (USFWS/NMFS 1998) and is 

consistent with procedures and methodology outlined in the Overview Document (U.S. 

EPA 2004) and reviewed by the U.S. Fish and Wildlife Service and National Marine 

Fisheries Service (USFWS/NMFS 2004). 

2.1 Purpose 

The purpose of this endangered species assessment is to evaluate potential direct and 

indirect effects on individuals of the federally threatened California red-legged frog 

(Rana aurora draytonii) (CRLF) arising from FIFRA regulatory actions regarding use of 

myclobutanil on almond, asparagus, canistel, cotton, grapes, hops, mamey (mamme 

apple), okra, peppermint, sapodilla, sapote white, spearmint, star apple, strawberry, and 

selected crops from the following crop groups: root and tuber; leafy, legume and fruiting 

vegetables; cucurbits; pome, stone and tropical fruits and berries. Non-food/non-feed 

uses include bluegrass and grasses grown for seed, various lawn and turf uses, cotton 

(seed), Douglas Fir (seed orchard, shelter belt), hybrid cottonwood/poplar plantations, 

loblolly and slash pine forest, ornamental and shade trees, ornamentals, woody shrubs 

and vines. In addition, this assessment evaluates whether use on these crops is expected 

to result in effects to the species’ designated critical habitat. This ecological risk 

assessment has been prepared consistent with a settlement agreement in the case Center 

for Biological Diversity (CBD) vs. EPA et al. (Case No. 02-1580-JSW(JL)) entered in 

Federal District Court for the Northern District of California on October 20, 2006. 

In this assessment, direct and indirect effects to the CRLF and potential effects to its 

designated critical habitat are evaluated in accordance with the methods described in the 

Agency’s Overview Document (U.S. EPA 2004). Screening level methods include use of 

standard models such as PRZM-EXAMS, T-REX, Terrplant and AgDRIFT, all of which 

are described at length in the Overview Document. Additional refinements include an 

analysis of the usage data, a spatial analysis and the use of the T-HERPS model. Use of 

17
such information is consistent with the methodology described in the Overview 

Document (U.S. EPA 2004), which specifies that “the assessment process may, on a 

case-by-case basis, incorporate additional methods, models, and lines of evidence that 

EPA finds technically appropriate for risk management objectives” (Section V, page 31 

of U.S. EPA 2004). 

In accordance with the Overview Document, provisions of the ESA, and the Services’ 

Endangered Species Consultation Handbook, the assessment of effects associated with 

registrations of myclobutanil is based on an action area. The action area is the area 

directly or indirectly affected by the federal action. It is acknowledged that the action 

area for a national-level FIFRA regulatory decision associated with a use of myclobutanil 

may potentially involve numerous areas throughout the United States and its Territories. 

However, for the purposes of this assessment, attention will be focused on relevant 

sections of the action area including those geographic areas associated with locations of 

the CRLF and its designated critical habitat within the state of California. As part of the 

“effects determination,” one of the following three conclusions will be reached regarding 

the potential use of myclobutanil in accordance with current labels: 

• “No effect”; 

• “May affect, but not likely to adversely affect”; or 

• “May affect and likely to adversely affect”. 

Designated critical habitat identifies specific areas that have the physical and biological 

features, (known as primary constituent elements or PCEs) essential to the conservation 

of the listed species. The PCEs for CRLFs are aquatic and upland areas where suitable 

breeding and non-breeding aquatic habitat is located, interspersed with upland foraging 

and dispersal habitat. 

If the results of initial screening-level assessment methods show no direct or indirect 

effects (no LOC exceedances) upon individual CRLFs or upon the PCEs of the species’ 

designated critical habitat, a “no effect” determination is made for use of myclobutanil as 

it relates to this species and its designated critical habitat. If, however, potential direct or 

indirect effects to individual CRLFs are anticipated or effects may impact the PCEs of the 

CRLF’s designated critical habitat, a preliminary “may affect” determination is made for 

the FIFRA regulatory action regarding myclobutanil. 

If a determination is made that use of myclobutanil within the action area(s) associated 

with the CRLF “may affect” this species or its designated critical habitat, additional 

information is considered to refine the potential for exposure and for effects to the CRLF 

and other taxonomic groups upon which these species depend (e.g., aquatic and terrestrial 

vertebrates and invertebrates, aquatic plants, riparian vegetation, etc.). Additional 

information, including spatial analysis (to determine the geographical proximity of CRLF 

habitat and myclobutanil use sites) and further evaluation of the potential impact of 

myclobutanil on the PCEs is also used to determine whether effects to designated critical 

habitat may occur. Based on the refined information, the Agency uses the best available 

information to distinguish those actions that “may affect, but are not likely to adversely 

18
affect” from those actions that “may affect and are likely to adversely affect” the CRLF. 

This information is presented as part of the Risk Characterization in Section 5 of this 

document. 

The Agency believes that the analysis of direct and indirect effects to listed species 

provides the basis for an analysis of potential effects on the designated critical habitat. 

Because myclobutanil is expected to directly impact living organisms within the action 

area (defined in Section 2.7), critical habitat analysis for myclobutanil is limited in a 

practical sense to those PCEs of critical habitat that are biological or that can be 

reasonably linked to biologically mediated processes (i.e., the biological resource 

requirements for the listed species associated with the critical habitat or important 

physical aspects of the habitat that may be reasonably influenced through biological 

processes). Activities that may affect critical habitat are those that alter the PCEs and 

appreciably diminish the value of the habitat. Evaluation of actions related to use of 

myclobutanil that may alter the PCEs of the CRLF’s critical habitat form the basis of the 

critical habitat impact analysis. Actions that may affect the CRLF’s designated critical 

habitat have been identified by the Services and are discussed further in Section 2.6. 

2.2 Scope 

The fungicide, myclobutanil is currently registered for both agricultural and nonagricultural uses in the State of California. 

The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory 

action) is an approved product label. The label is a legal document that stipulates how 

and where a given pesticide may be used. Product labels (also known as end-use labels) 

describe the formulation type (e.g., liquid or granular), acceptable methods of application, 

approved use sites, and any restrictions on how applications may be conducted. Thus, the 

use or potential use of myclobutanil in accordance with the approved product labels for 

California is “the action” relevant to this ecological risk assessment. 

Although current registrations of myclobutanil allow for use nationwide, this ecological 

risk assessment and effects determination addresses currently registered uses of 

myclobutanil in portions of the action area that are reasonably assumed to be biologically 

relevant to the CRLF and its designated critical habitat. Further discussion of the action 

area for the CRLF and its critical habitat is provided in Section 2.7. 

1,2,4-triazole and its conjugates are common metabolites to the triazole class of 

compounds, including myclobutanil. Only the 1,2,4-triazole degradate was identified in 

soil and water metabolism studies. The percentage of 1,2,4-triazole reached a high of 

18% in the aerobic soil metabolism study with 13 % remaining at the termination of a 

367 day study. Because only a limited amount of environmental fate data for 1,2,4-

triazole are available, its concentration can not be estimated. For the aquatic exposure 

assessment, concentrations of parent myclobutanil and the total residues (myclobutanil 

plus 1,2,4-triazole) are estimated. The total residues for aquatic exposure is conservative 

if the toxicity of the 1,2,4-triazole is less than or equal to the toxicity of myclobutanil. 

19
For the terrestrial exposure assessment, a conservative default foliar dissipation half-life 

of 35 days is used to account for terrestrial exposure to the parent, the primary plant 

metabolite RH-9090, the 1,2,4-triazole degradate and the triazole conjugates (triazole 

alanine and triazole acetic acid). Crop-specific residue decline data on combined residues 

of myclobutanil and the primary metabolite RH-9090, provide a range of half-lives from 

14 to 26 days. Since no decline data are available for the 1,2,4-triazole and triazole 

conjugates, toxicity data on the degradates indicate that they are either equivalent to or 

less toxic than the parent and structure-activity analyses indicate that RH-9090 is likely to 

be of equivalent toxicity to the parent, the default 35 day half-life is selected for use in 

estimating terrestrial exposure. 

The Agency does not routinely include in its risk assessments an evaluation of mixtures 

of active ingredients, either those mixtures of multiple active ingredients in product 

formulations or those in the applicator’s tank. In the case of the product formulations of 

active ingredients (that is, a registered product containing more than one active 

ingredient), each active ingredient is subject to an individual risk assessment for 

regulatory decision regarding the active ingredient on a particular use site. If effects data 

are available for a formulated product containing more than one active ingredient, they 

may be used qualitatively or quantitatively in accordance with the Agency’s Overview 

Document and the Services’ Evaluation Memorandum (U.S., EPA 2004; USFWS/NMFS 

2004). 

Myclobutanil has registered products that contain multiple active ingredients. Analysis 

of the available open literature and acute oral mammalian LD50 data for multiple active 

ingredient products relative to the single active ingredient is provided in Appendix A. 

The results of this analysis show that an assessment based on the toxicity of the single 

active ingredient of myclobutanil is appropriate. All products with available acute 

toxicity data had oral LD50 values of greater than 5000 mg/kg. Because the active 

ingredients are not expected to have similar mechanisms of action, metabolites, or 

toxicokinetic behavior, it is reasonable to conclude that an assumption of dose-addition 

would be inappropriate. Consequently, an assessment based on the toxicity of 

myclobutanil is the only reasonable approach that employs the available data to address 

the potential acute risks of the formulated products. 

2.3 Previous Assessments 

Myclobutanil was registered in the U.S. after 1984 and has not been through the 

reregistration process. Myclobutanil has been assessed a number of times for new uses 

including Section 18 assessments. Based on the various past assessments, in general, risk 

tended to be greatest for freshwater fish (acute), marine/estuarine invertebrates (acute), 

birds (acute and chronic), and mammals (acute and chronic) depending on the use 

patterns and application rates. To date, no data on toxicity of myclobutanil to terrestrial 

plants, aquatic vascular plants, and chronic exposure to invertebrates (freshwater and 

marine/estuarine) or marine/estuarine fish have been submitted to the Agency for review 

and so risk has not been assessed quantitatively. Furthermore, certain toxicity data were 

not available (e.g. chronic exposure to birds and acute exposure to marine/estuarine 

organisms (fish and invertebrates) and aquatic non-vascular plants) at the time when 

20
some uses were assessed; however, that data have been subsequently obtained and used 

in risk assessments of other uses. 

2.4 Stressor Source and Distribution 

2.4.1 Physical and Chemical Properties 

Selected physical and chemical properties of myclobutanil are summarized below. 

Common name: Myclobutanil 

Chemical name: 

(CAS): 

 alpha-butyl-alpha (4-chlorophenyl)-1H-1,2-triazole-1-propane-nitrile 

(IUPAC): 

 (RS)-2-(4-chlorophenyl)-2-(1H-1,2,4-triazol-1-ylmethyl)hexanentrile 

Chemical structure: 

Cl

N

N

N

3CH

CN

Molecular formula C15H17ClN4

Molecular weight 288.8 g/mol 

Physical state: White crystalline solid 

Melting point: 63 to 68 oC 

Solubility: 142 mg/L water @ 25 oC and pH 7 

124 mg/L @ 20 oC 

Vapor pressure 1.49 x 10-06 mm Hg at 25 oC 

Henry’s Law constant 

3.25 x 10-06 atm m3

/mole @ 25 oC 

1.75 x 10-07 unitless @ 20 oC 

Log Octanol/Water partition 

coefficient: 2.89 @ pH 7 and 20 oC 

Dissociation Constant, 

(pKa) 2.3 @ 25 oC 

21
2.4.2 Environmental Fate Assessment 

Available environmental fate parameters of myclobutanil and 1,2,4-triazole degradate are 

listed in Table 2.1. These data are based on studies that were conducted prior to 1986 

before Good Laboratory Practice (GLP) standards (40 CFR 160) and data requirements 

for registration were promulgated in the Code of Federal Regulations (40 CFR 158). The 

previously submitted studies have not been re-reviewed, although rate of degradation 

(i.e., half-life) of myclobutanil in the aerobic soil metabolism study was re-estimated. 

Due to its persistence and mobility, the primary routes of dissipation are through 

leaching, runoff, and spray drift. Myclobutanil has been detected in rain in several 

agricultural watersheds in California (Vogel et al., 2008); thus, there is also a potential 

for atmospheric transport. Myclobutanil is stable to hydrolysis and to photolysis. 

Myclobutanil degradation is controlled by microbial-mediated transformations. 

Myclobutanil was moderately persistent to persistent (DT50 > 70 days) in aerobic soils 

and persistent in anaerobic soils. The major degradation products observed in the aerobic 

soil metabolism (ASM) studies were 1,2,4-triazole (maximum 18%), CO2, a polar 

degradate (β-4-chlorophenyl-β-cyano-γ-(1H-1,2,4-triazole)-butyric acid; (maximum 9 

%), and unextractable residues. At the conclusion of the 367 day ASM study, 29 to 33 

percent of the applied radioactivity remained as parent myclobutanil and 13 percent was 

identified as 1,2,4-triazole. 

Myclobutanil degradation in the aerobic soil metabolism (ASM) studies does not appear 

to follow first-order kinetics based upon visual inspection, but follows a “hockey stick” 

degradation pattern (a rapid initial decline followed by a slower decline), thus the firstorder half-life does not accurately describe the decline of myclobutanil residues. The 

observed (visible inspection) aerobic metabolism DT50 value for myclobutanil ranged 

between 75 and 90 days. The DT90 for myclobutanil was not reached during the course 

of the study (367 days). Once the maximum level of 1,2,4-triazole is reached, its decline 

pattern parallels myclobutanil. The decline of the combined residues also followed the 

hockey stick pattern. Myclobutanil photo-degrades with a half-life of approximately 143 

days on soil. Thus, myclobutanil residues are fairly persistent. Terrestrial field dissipation 

half-life values ranged from 92 to 292 days. Generally, half-lives estimated in terrestrial 

field dissipation studies are less than aerobic soil metabolism studies because they 

include other dissipation pathways in addition to metabolism. The study with the 292 day 

terrestrial field dissipation half-life was conducted in California. Leaching was not a 

significant dissipation pathway. The potential for accumulation in soil and sediment is 

possible due to the persistence, especially when there are multiple applications. Further 

discussion is provided in Section 3.2.5, Aquatic Exposure Modeling and Appendix B. In 

an aerobic soil metabolism study the half-life of 1,2,4-triazole was estimated as 315 days. 

Because log Kows for parent and degradation products are low (log Kow= 2.94), the 

myclobutanil residues are not expected to bioaccumulate (MRID # 00162541). 

Table 2.1 lists the selected physical and environmental fate properties of myclobutanil, 

along with the major and minor degradate products detected in the submitted 

22
environmental fate and transport studies. The submitted study citations can be found in 

Appendix O. 

Table 2.1 Summary of Myclobutanil and 1,2,4-triazole Physical and Environmental 

Fate Properties 

Study Value (units) Major Degradates 

Minor Degradates

MRID # 

or Data 

Source 

Study Status 

Molecular Weight 288.8 g/mol - 

Vapor Pressure 1.49 x 10-06 mm Hg at 25 oC 

1.6 x 10-06 mm Hg 

- D190680 - 

Henry’s Law 

Constant 3.25 x 10-09 atm m3

/mole @ 25 oC - calculated - 

Laboratory 

Volatility No data - - No study submitted 

Log Kow log Kow= 2.94 - 00162541 

Hydrolysis Stable at pH 5, 7, and 9 - 001416-79 Acceptable 

Direct Aqueous 

Photolysis Stable - 

40641501 

40319801 

40528801 

Acceptable 

Photolysis on soil 143 days 1,2,4-triazole 00164988 Acceptable 

Photodegradation 

in air No data - - No study submitted 

Aerobic Soil 

Metabolism 198, 2441

 days 

1,2,4-triazole, CO2 and 

β-4-chlorophenyl-β-cyanoγ (1H-1,2,4—triazole)-

butyric acid 

00164561 Acceptable 

Anaerobic Soil 

Metabolism 

Assumed stable, No appreciable 

degradation in 62 days. 1,2,4-triazole No MRID Acceptable 

Anaerobic Aquatic 

Metabolism 

No data - - No study 

submitted 

Aerobic Aquatic 

Metabolism 

No data - - No study 

submitted 

Mobility 

Myclobutanil 

Freundlich Kads - 

1.46, 2.39, 4.44, 7.08, 9.77 mL/g 

(1/n – 0.89 to 1.02) 

Koc2

1,2,4-triazole 

Freundlich Kads - 

 0.19 to 3.35 mL/g 

(1/n – 0.65 to 0.85) 

Koc2

141602 

40891501 Acceptable 

Terrestrial Field 

Dissipation 92 to 292 days 164563 Acceptable 

1

 Half-lives were recalculated (Appendix C) by EFED (D336254). 2

 Koc not valid, sorption does not appear to be correlated with soil organic carbon (D336254). 

23
The metabolite/degradate 1,2,4-triazole has been detected in plant and animal metabolism 

studies. However, a number of other degradates or metabolites not identified in soil and 

water studies have been identified in plant and animal metabolism. These include 

triazole-analine (TA) and triazole acetic acid (TTA). 

The following figures provide the structures of the degradates/metabolites discussed in 

this assessment. 

NH

N N

1,2,4-Triazole 

(a.k.a. 1,2,4-T; free triazole) 

1-H-1,2,4-triazole 

N

N

N

N H 2

O O H

Triazole Alanine 

(a.k.a. TA) 

α-Amino-1H-1,2,4-triazole1-propanoic acid 

N

N

N

O

OH

Triazole Acetic Acid 

(a.k.a. TAA) 

1H-1,2,4-Triazole-1-acetic 

acid 

Chemical structures for 1,2,4-triazole, triazole alanine, and triazole acetic acid 

Figure 2.1 Myclobutanil Degradates 

Cl

C

N

HO

CH3

NH

N

N

Figure 2.2 Myclobutanil Terrestrial Plant Metabolite 

RH-9090 (α-(3-hydroxybutyl)-α-(4-chlorophenyl)-1H-1,2,4-triazole-1-propanenitrile) 

24
2.4.3 Environmental Transport Assessment 

Potential transport mechanisms include pesticide surface water runoff, spray drift, and 

secondary drift of volatilized or soil-bound residues leading to deposition onto nearby or 

more distant ecosystems. Surface water runoff and spray drift are expected to be the 

major routes of exposure for myclobutanil. The USGS NAWQA Program has detected 

myclobutanil residues in surface water samples collected in California (USGS, 2009). 

Myclobutanil has been detected in rain in an agricultural watersheds sampled in 

California (Vogel et al., 2008). Thus, there appears to a potential for atmospheric 

transport of myclobutanil. 

Myclobutanil is mobile as indicated by the Freundlich Kads values (from 1.46 to 9.77 

mL/g) (Table 2.1). The lowest non-sand value is 2.39 mL/g. Desorption coefficients 

were generally less than the sorption coefficients. The degradate (1,2,4-triaziole) has 

lower Freundlich Kads values (0.234 to 0.833 mL/g), suggesting it would be more mobile 

than the parent compound (Table 2.1). The sorption is not strongly correlated to soil 

organic carbon (matter), thus Koc is not a good measure of mobility for modeling. 

A number of studies have documented atmospheric transport and re-deposition of 

pesticides from the Central Valley to the Sierra Nevada Mountains (Fellers et al., 2004, 

Sparling et al., 2001, LeNoir et al., 1999, and McConnell et al., 1998). Myclobutanil was 

detected in rain water in a study partially conducted in California (Vogel et al., 2008). 

Prevailing winds blow across the Central Valley eastward to the Sierra Nevada 

Mountains, transporting airborne industrial and agricultural pollutants into the Sierra 

Nevada ecosystems (Fellers et al., 2004, LeNoir et al., 1999, and McConnell et al., 1998). 

Several sections of critical habitat for the CLRF are located east of the Central Valley. 

The magnitude of transport via secondary drift depends on the ability of myclobutanil to 

be mobilized into air and its eventual removal through wet and dry deposition of 

gases/particles and photochemical reactions in the atmosphere. Therefore, 

physicochemical properties of myclobutanil that describe its potential to enter the air 

from water or soil (e.g., Henry’s Law constant and vapor pressure), pesticide use data, 

modeled estimated concentrations in water and air, and available air monitoring data 

from the Central Valley and the Sierra Nevadas are considered in evaluating the potential 

for atmospheric transport of myclobutanil to locations where it could impact the CRLF. 

In general, deposition of drifting or volatilized pesticides is expected to be greatest close 

to the site of application. Computer models of spray drift (AgDRIFT) are used to 

determine potential exposures to terrestrial organisms via spray drift. The distance of 

potential impact away from the use sites is determined by the distance required to fall 

below the chronic LOC for mammals. 

2.4.4 Mechanism of Action 

Myclobutanil is a triazole fungicide in the conazole class of fungicides which is a 

systemic fungicide used to control powdery mildew on a number of crops. Myclobutanil 

25
appears to be a specific inhibitor of sterol 14-demethylase, which disrupts the ergosterol 

biosynthesis pathway which is vital to fungal cell wall formation. It is classified as a 

demethylation inhibitor (DMI) fungicide. 

2.4.5 Use Characterization 

Analysis of labeled use information is the critical first step in evaluating the federal 

action. The current label for myclobutanil represents the FIFRA regulatory action; 

therefore, labeled use and application rates specified on the label form the basis of this 

assessment. The assessment of use information is critical to the development of the 

action area and selection of appropriate modeling scenarios and inputs. 

Myclobutanil is a triazole fungicide in the conazole class of fungicides. It is a systemic 

fungicide used to control powdery mildew. It is registered for use on variety of terrestrial 

food and feed crops and terrestrial non-food crops. Myclobutanil is formulated as a 

wettable powder (2-40% a.i.) or as an emulsifiable concentrate (1-25% a.i.), granular 

(<1% a.i.), dust (5% a.i.), dry flowable (60% a.i.), and ready to use (<1% a.i.). 

Application rates range from 0.04 to 5.0 lbs a.i./acre. Myclobutanil is applied at multiple 

growth stages (e.g., seed treatment, pre-bloom, bloom, foliar, post-bloom etc.). 

Application equipment includes hand held devices for both liquids and solids (e.g., 

trigger spray bottle, aerosol can, shaker jar, high and low volume sprayers), 

chemigation/irrigation (e.g., sprinkler, solid state), spreader, groundboom, and aircraft. 

Myclobutanil is also used to treat cotton seed. The formulation for this use is a 25% ai 

EC. The application rate for cotton is 0.06 lb ai per hundred weight (cwt). Planting 

depth for cotton seeds varies depending on soil moisture and soil texture. Most labels 

include the following restrictions/prohibitions: do not apply directly to water or to areas 

where surface water is present or to intertidal areas below the mean high water mark; do 

not apply directly to water; do not apply when drift is likely to occur; do not apply where 

runoff is likely to occur. Table 2.2 presents the uses and corresponding application rates 

and methods of application considered in this assessment. 

Table 2.2 Myclobutanil Uses Assessed for the CRLF 

Use Max Single 

Application 

Rate (lb ai/A) 

Max Number 

of 

Applications 

Number of 

Crop Cycles 

Per Year a b

Max Seasonal/Yearly 

Application Rate 

(lb ai/A) 

Minimum 

Application 

Interval 

Non-Food/Non-Feed Uses

Turf 

Commercial 

Residential Lawn 

Golf Course 

1.3 

(0.03lb/1Kft2

) 

4 1 NS 5 

Grass grown for 

seed 

0.19 NS 1 NS 14 

Cotton (seed) 0.06 lb cwt NS NS NS NS 

Forest 

Douglas Fir 

Loblolly Pine 

0.25 NS 1 0.6 14 

Cottonwood/ 0.15 NS 1 0.6 10 

26
Use Max Single 

Application 

Rate (lb ai/A) 

Max Number 

of 

Applications 

Number of 

Crop Cycles 

Per Year a b

Max Seasonal/Yearly Minimum 

Application Rate Application 

(lb ai/A) Interval 

Poplar Plantation 

Ornamentals 

Shade Trees 

Groundcover 

Herbaceous Plant 

Woody Scrubs/vines 

0.26 NS 1 2.0 10 

Ornamental Sod 

Farm 

0.6 

(0.014lb/1Kft2

) 

1 NS 

Slash Pine 0.003 lb ai/gal NS 1 14 

Food/Feed Uses

Almond 0.2 3/cc 3/yr 1 0.6 7 

Apple 0.5 10/cc 1 2.0 7 

Apricot 0.5 7/cc 1 1.0 7 

Artichokes 0.1 6/cc 1 0.6 14 

Asparagus 0.125 6/cc 1 0.75 14 

Beans, Green 0.125 4/cc 1 0.5 7 

Blackberry 0.125 4/cc 4/yr 1 0.5 10 

Boysenberry 0.1 NS 1 0.25 10 

Canistel 0.25 8/cc 1 2.0 14 

Carrot 0.2 NS 1 0.375 14 

Cherry 0.5 7/cc 7/yr 1 1.3 7 

Cucurbit Vegetables 

Balsam Pear 

Cantaloupe 

Casaba 

Honeydew Melon 

Watermelon 

Cucumber 

Pumpkin 

Squash 

0.125 Melon 7/cc 

7/yr 

Other 5 cc 

1 0.6 7 

Currant 0.125 8/cc 1 1.0 7 

Dewberry 0.0625 NS 1 0.25 10 

Eggplant 0.125 4/cc 1 0.5 10 

Gooseberry 0.125 8/cc 1 1.0 10 

Grapes 0.13 6/cc 1 0.6 7 

Hops 0.25 4/cc 1 1.0 7 

Lettuce 0.125 4/cc 2 0.5 14 

Mango 0.25 8/cc 1 2.0 14 

Mayhaw 0.25 10/cc 1 2.0 7 

Nectarine 0.5 7/yr 1 1.3 7 

Okra 0.125 4/cc 1 0.5 10 

Papaya 0.25 8/cc 1 2.0 14 

Peach 0.5 7/cc 7/yr 1 1.3 7 

Pepper 0.125 NS 1 0.5 10 

Plum 0.16 7/cc 7/yr 1 1.1 7 

Prune 0.15 7/cc 7/yr 1 1.1 7 

Raspberry 0.125 4/cc 1 0.25 10 

Sapodilla 0.25 8/cc 1 2.0 14 

Strawberry 0.125 6/cc 1 0.75 14 

Sugar Beet 0.19 NS 1 NS NS 

Tomato 0.1 4/cc 1 0.5 21 

27
Use Max Single 

Application 

Rate (lb ai/A) 

Max Number 

of 

Applications 

Number of 

Crop Cycles 

Per Year a b

Max Seasonal/Yearly Minimum 

Application Rate Application 

(lb ai/A) Interval 

Youngberry 0.0625 NS 1 0.25 10 a Number of crop cycles per year for all crops except lettuce as assumed by EFED. 

b Number of crop cycles for lettuce USEPA 2007 - Memo from Anisha Kaul (BEAD) to Melissa Panger (EFED). Maximum Number 

of Crop Cycles Per Year in California for Methomyl Use Sites 2/28 

NS = Not specified 

U.S. Geological Survey (USGS) National Water Quality Assessment Program 

(NAWQA) data indicate that in 2002, myclobutanil was used on agricultural crops 

predominantly in California, and Washington, with high usage also in Wisconsin, 

Michigan and a number northern and mid Atlantic states (Figure 2.3). At that time, the 

use of myclobutanil on grapes, apples and almonds represented more than 80% of the 

national use. Based on national usage data compiled by the Biological and Economic 

Analysis Division (BEAD) primarily from 2001 to 2006, on average, roughly 159,000 

pounds of myclobutanil are applied annually to agricultural crops. These data show that 

usage is highest on grapes, almonds and apples with annual average applications 50,000, 

40,000, and 20,000 lbs. a.i. respectively. The crop with the highest average percent crop 

treated with myclobutanil is artichokes (65%). 

Figure 2.3 Map of Estimated Annual Agricultural Use of Myclobutanil in 2002

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m5036 

28
Use data specific to California are available from the California Department of Pesticide 

Regulation’s (CDPR) Pesticide Use Reporting (PUR) database, which includes every 

pesticide application made by professional applicators. BEAD summarized these data, 

from 1999 to 2006, to the county level by site, pesticide, and unit treated. Based on this 

analysis, California accounts for approximately 50% of national usage. An average of 

81,868 lbs of myclobutanil was applied in California to an average of 763,456 acres per 

year. Use in California was at a maximum of 95,411 lbs in 2000 and at a minimum of 

70,735 lbs in 2006. Usage ranged from 70,000 to 84,000 lbs between 2003 and 2006. 

From 1999-2006, myclobutanil was used in a total of 54 counties involving 41 different 

uses. Five counties accounted for 50% of the total lbs applied on average per county 

[Fresno (14%), Kern (16%), Monterey (11%), San Joaquin (6.5%) and Tulare (10%)]. 

Each of the other counties used <5% of the total lbs applied. Grapes (table and wine) 

accounted for approximately 60% of the total lbs applied per year in CA on average. 

Other major crops include almonds (10%) and strawberries (6%). All other crops 

accounted for <5% of the total usage on a per crop basis. This analysis may not be 

entirely representative of current use patterns because labeled uses may have changed 

since these data were collected, and because it may also include misreporting. A 

summary of myclobutanil usage for all California use sites is provided below in Table 

2.3. Complete data from the BEAD analysis of the CDPR PUR database are presented in 

Appendix D. 

Table 2.3 Summary of California Department of Pesticide Registration (CDPR) 

Pesticide Use Reporting (PUR) Data from 1999 to 2006 for Currently Registered 

Myclobutanil Uses 

Site Name Average Pounds 

All Uses 

Avg App Rate 

All Uses 

lbs a.i./A 

Avg 95th% 

App Rate 

lbs a.i./A 

Avg 99th% 

App Rate 

lbs a.i./A 

Avg Max App 

Rate 

lbs a.i./A 

Almond 426 0.16 0.24 0.41 0.80

Apple 44 0.12 0.21 0.28 0.40

Apricot 15 0.11 0.16 0.19 0.28

Artichoke 103 0.09 0.10 0.13 0.29

Asparagus 46 0.12 0.13 0.13 0.40

Beans, Green 2 0.12 0.14 0.14 0.14

Cantaloupe 0.4 0.09 0.11 0.12 0.12

Cherry 40 0.10 0.14 0.19 0.40

Cucumber 4 0.10 0.11 0.13 0.13

Grape 644 0.10 0.14 0.19 0.41

Melon 17 0.10 0.11 0.20 0.20

Nectarine 40 0.13 0.18 0.21 0.35

Peach 34 0.12 0.21 0.28 0.47

Pepper 48 0.16 0.19 0.21 0.23

Plum 42 0.11 0.14 0.39 0.58

Prune 12 0.12 0.14 0.14 0.21

Pumpkin 8 0.12 0.23 0.29 0.29

Raspberry 7 0.07 0.09 0.17 0.28

Squash 3 0.11 0.12 0.12 0.12

Strawberry 193 0.10 0.14 0.21 0.40

Tomato 38 0.10 0.11 0.21 0.23

29
Site Name Average Pounds 

All Uses 

Avg App Rate 

All Uses 

lbs a.i./A 

Avg 95th% 

App Rate 

lbs a.i./A 

Avg 99th% Avg Max App 

App Rate Rate 

lbs a.i./A lbs a.i./A 

Watermelon 29 0.10 0.12 0.12 0.13

Greenhouse 6 0.11 0.22 0.40 0.55

Landscaping 33 0.46 0.47 0.47 0.47

Rights of Way 0.5 0.07 0.09 0.09 0.09

Turf/Sod 5 1.15 1.36 1.41 1.41

2.5 Assessed Species 

The CRLF was federally listed as a threatened species by USFWS effective June 24, 

1996 (USFWS 1996). It is one of two subspecies of the red-legged frog and is the largest 

native frog in the western United States (USFWS 2002). A brief summary of information 

regarding CRLF distribution, reproduction, diet, and habitat requirements is provided in 

Sections 2.5.1 through 2.5.4, respectively. Further information on the status, distribution, 

and life history of and specific threats to the CRLF is provided in Attachment I. 

Final critical habitat for the CRLF was designated by USFWS on April 13, 2006 

(USFWS 2006; 71 FR 19244-19346). Further information on designated critical habitat 

for the CRLF is provided in Section 2.6. 

2.5.1 Distribution 

The CRLF is endemic to California and Baja California (Mexico) and historically 

inhabited 46 counties in California including the Central Valley and both coastal and 

interior mountain ranges (USFWS 1996). Its range has been reduced by about 70%, and 

the species currently resides in 22 counties in California (USFWS 1996). The species has 

an elevational range of near sea level to 1,500 meters (5,200 feet) (Jennings and Hayes 

1994); however, nearly all of the known CRLF populations have been documented below 

1,050 meters (3,500 feet) (USFWS 2002). 

Populations currently exist along the northern California coast, northern Transverse 

Ranges (USFWS 2002), foothills of the Sierra Nevada (5-6 populations), and in southern 

California south of Santa Barbara (two populations) (Fellers 2005a). Relatively larger 

numbers of CRLFs are located between Marin and Santa Barbara Counties (Jennings and 

Hayes 1994). A total of 243 streams or drainages are believed to be currently occupied 

by the species, with the greatest numbers in Monterey, San Luis Obispo, and Santa 

Barbara counties (USFWS 1996). Occupied drainages or watersheds include all bodies 

of water that support CRLFs (i.e., streams, creeks, tributaries, associated natural and 

artificial ponds, and adjacent drainages), and habitats through which CRLFs can move 

(i.e., riparian vegetation, uplands) (USFWS 2002). 

The distribution of CRLFs within California is addressed in this assessment using four 

categories of location including recovery units, core areas, designated critical habitat, and 

known occurrences of the CRLF reported in the California Natural Diversity Database 

30
(CNDDB) that are not included within core areas and/or designated critical habitat (see 

(see Figure 2.4 Recovery Unit, Core Area, Critical Habitat and Occurrence Designations 

for CRLF). Recovery units, core areas, and other known occurrences of the CRLF from 

the CNDDB are described in further detail in Attachment I, and designated critical habitat 

is addressed in Section 2.6. Recovery units are large areas defined at the watershed level 

that have similar conservation needs and management strategies. The recovery unit is 

primarily an administrative designation, and land area within the recovery unit boundary 

is not exclusively CRLF habitat. Core areas are smaller areas within the recovery units 

that comprise portions of the species’ historic and current range and have been 

determined by USFWS to be important in the preservation of the species. Designated 

critical habitat is generally contained within the core areas, although a number of critical 

habitat units are outside the boundaries of core areas, but within the boundaries of the 

recovery units. Additional information on CRLF occurrences from the CNDDB is used 

to cover the current range of the species not included in core areas and/or designated 

critical habitat, but within the recovery units. 

31
Recovery Units

1. Sierra Nevada Foothills and Central Valley

2. North Coast Range Foothills and Western 

Sacramento River Valley

3. North Coast and North San Francisco Bay

4. South and East San Francisco Bay

5. Central Coast

6. Diablo Range and Salinas Valley

7. Northern Transverse Ranges and Tehachapi

Mountains

8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River

2. Yuba River- S. Fork Feather River

3. Traverse Creek/ Middle Fork/ American R. Rubicon

4. Cosumnes River

5. South Fork Calaveras River*

6. Tuolumne River*

7. Piney Creek*

8. Cottonwood Creek

9. Putah Creek – Cache Creek*

10. Lake Berryessa Tributaries

11. Upper Sonoma Creek

12. Petaluma Creek – Sonoma Creek

13. Pt. Reyes Peninsula

14. Belvedere Lagoon

15. Jameson Canyon – Lower Napa River

16. East San Francisco Bay

17. Santa Clara Valley

18. South San Francisco Bay

19. Watsonville Slough-Elkhorn Slough

20. Carmel River – Santa Lucia

21. Gablan Range

22. Estero Bay

23. Arroyo Grange River

24. Santa Maria River – Santa Ynez River

25. Sisquoc River

26. Ventura River – Santa Clara River

27. Santa Monica Bay – Venura Coastal Streams

28. Estrella River

29. San Gabriel Mountain*

30. Forks of the Mojave*

31. Santa Ana Mountain*

32. Santa Rosa Plateau

33. San Luis Ray*

34. Sweetwater*

35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map

Recovery Units

1. Sierra Nevada Foothills and Central Valley

2. North Coast Range Foothills and Western 

Sacramento River Valley

3. North Coast and North San Francisco Bay

4. South and East San Francisco Bay

5. Central Coast

6. Diablo Range and Salinas Valley

7. Northern Transverse Ranges and Tehachapi

Mountains

8. Southern Transverse and Peninsular Ranges

Core Areas

1. Feather River

2. Yuba River- S. Fork Feather River

3. Traverse Creek/ Middle Fork/ American R. Rubicon

4. Cosumnes River

5. South Fork Calaveras River*

6. Tuolumne River*

7. Piney Creek*

8. Cottonwood Creek

9. Putah Creek – Cache Creek*

10. Lake Berryessa Tributaries

11. Upper Sonoma Creek

12. Petaluma Creek – Sonoma Creek

13. Pt. Reyes Peninsula

14. Belvedere Lagoon

15. Jameson Canyon – Lower Napa River

16. East San Francisco Bay

17. Santa Clara Valley

18. South San Francisco Bay

19. Watsonville Slough-Elkhorn Slough

20. Carmel River – Santa Lucia

21. Gablan Range

22. Estero Bay

23. Arroyo Grange River

24. Santa Maria River – Santa Ynez River

25. Sisquoc River

26. Ventura River – Santa Clara River

27. Santa Monica Bay – Venura Coastal Streams

28. Estrella River

29. San Gabriel Mountain*

30. Forks of the Mojave*

31. Santa Ana Mountain*

32. Santa Rosa Plateau

33. San Luis Ray*

34. Sweetwater*

35. Laguna Mountain*

* Core areas that were historically occupied by the California red-legged frog are not included in the map

Figure 2.4 Recovery Unit, Core Area, Critical Habitat and Occurrence Designations 

for CRLF

32
Other Known Occurrences from the CNDBB 

The CNDDB provides location and natural history information on species found in 

California. The CNDDB serves as a repository for historical and current species location 

sightings. Information regarding known occurrences of CRLFs outside of the currently 

occupied core areas and designated critical habitat is considered in defining the current 

range of the CRLF. See: http://www.dfg.ca.gov/bdb/html/cnddb_info.html for additional 

information on the CNDDB. 

2.5.2 Reproduction 

CRLFs breed primarily in ponds; however, they may also breed in quiescent streams, 

marshes, and lagoons (Fellers 2005a). According to the Recovery Plan (USFWS 2002), 

CRLFs breed from November through late April. Peaks in spawning activity vary 

geographically; Fellers (2005b) reports peak spawning as early as January in parts of 

coastal central California. Eggs are fertilized as they are being laid. Egg masses are 

typically attached to emergent vegetation, such as bulrushes (Scirpus spp.) and cattails 

(Typha spp.) or roots and twigs, and float on or near the surface of the water (Hayes and 

Miyamoto 1984). Egg masses contain approximately 2000 to 6000 eggs ranging in size 

between 2 and 2.8 mm (Jennings and Hayes 1994). Embryos hatch 10 to 14 days after 

fertilization (Fellers 2005a) depending on water temperature. Egg predation is reported 

to be infrequent and most mortality is associated with the larval stage (particularly 

through predation by fish); however, predation on eggs by newts has also been reported 

(Rathburn 1998). Tadpoles require 11 to 28 weeks to metamorphose into juveniles 

(terrestrial-phase), typically between May and September (Jennings and Hayes 1994, 

USFWS 2002); tadpoles have been observed to over-winter (delay metamorphosis until 

the following year) (Fellers 2005b, USFWS 2002). Males reach sexual maturity at 2 

years, and females reach sexual maturity at 3 years of age; adults have been reported to 

live 8 to 10 years (USFWS 2002). 

J F M A M J J A S O N D

Light Blue = Breeding/Egg Masses

Green = Tadpoles (except those that over-winter)

Orange = Young Juveniles

Adults and juveniles can be present all year

J F M A M J J A S O N D

Light Blue = Breeding/Egg Masses

Green = 

Orange = Young Juveniles

Adults and juveniles can be present all year

Tadpoles (except those that over-winter)

Figure 2.5 CRLF Reproductive Events by Month 

33
2.5.3 Diet 

Although the diet of CRLF aquatic-phase larvae (tadpoles) has not been studied 

specifically, it is assumed that their diet is similar to that of other frog species, with the 

aquatic phase feeding exclusively in water and consuming diatoms, algae, and detritus 

(USFWS 2002). Tadpoles filter and entrap suspended algae (Seale and Beckvar, 1980) 

via mouthparts designed for effective grazing of periphyton (Wassersug, 1984, 

Kupferberg et al.; 1994; Kupferberg, 1997; Altig and McDiarmid, 1999). 

Juvenile and adult CRLFs forage in aquatic and terrestrial habitats, and their diet differs 

greatly from that of larvae. The main food source for juvenile aquatic- and terrestrialphase CRLFs is thought to be aquatic and terrestrial invertebrates found along the 

shoreline and on the water surface. Hayes and Tennant (1985) report, based on a study 

examining the gut content of 35 juvenile and adult CRLFs, that the species feeds on as 

many as 42 different invertebrate taxa, including Arachnida, Amphipoda, Isopoda, 

Insecta, and Mollusca. The most commonly observed prey species were larval alderflies 

(Sialis cf. californica), pillbugs (Armadilliadrium vulgare), and water striders (Gerris sp). 

The preferred prey species, however, was the sowbug (Hayes and Tennant, 1985). This 

study suggests that CRLFs forage primarily above water, although the authors note other 

data reporting that adults also feed under water, are cannibalistic, and consume fish. For 

larger CRLFs, over 50% of the prey mass may consists of vertebrates such as mice, frogs, 

and fish, although aquatic and terrestrial invertebrates were the most numerous food 

items (Hayes and Tennant 1985). For adults, feeding activity takes place primarily at 

night; for juveniles feeding occurs during the day and at night (Hayes and Tennant 1985). 

2.5.4 Habitat 

CRLFs require aquatic habitat for breeding, but also use other habitat types including 

riparian and upland areas throughout their life cycle. CRLF use of their environment 

varies; they may complete their entire life cycle in a particular habitat or they may utilize 

multiple habitat types. Overall, populations are most likely to exist where multiple 

breeding areas are embedded within varying habitats used for dispersal (USFWS 2002). 

Generally, CRLFs utilize habitat with perennial or near-perennial water (Jennings et al. 

1997). Dense vegetation close to water, shading, and water of moderate depth are habitat 

features that appear especially important for CRLF (Hayes and Jennings 1988). 

Breeding sites include streams, deep pools, backwaters within streams and creeks, ponds, 

marshes, sag ponds (land depressions between fault zones that have filled with water), 

dune ponds, and lagoons. Breeding adults have been found near deep (0.7 m) still or slow 

moving water surrounded by dense vegetation (USFWS 2002); however, the largest 

number of tadpoles have been found in shallower pools (0.26 – 0.5 m) (Reis, 1999). Data 

indicate that CRLFs do not frequently inhabit vernal pools, as conditions in these habitats 

generally are not suitable (Hayes and Jennings 1988). 

CRLFs also frequently breed in artificial impoundments such as stock ponds, although 

additional research is needed to identify habitat requirements within artificial ponds 

34
(USFWS 2002). Adult CRLFs use dense, shrubby, or emergent vegetation closely 

associated with deep-water pools bordered with cattails and dense stands of overhanging 

vegetation (http://www.fws.gov/endangered/features/rl_frog/rlfrog.html#where). 

In general, dispersal and habitat use depends on climatic conditions, habitat suitability, 

and life stage. Adults rely on riparian vegetation for resting, feeding, and dispersal. The 

foraging quality of the riparian habitat depends on moisture, composition of the plant 

community, and presence of pools and backwater aquatic areas for breeding. CRLFs can 

be found living within streams at distances up to 3 km (2 miles) from their breeding site 

and have been found up to 30 m (100 feet) from water in dense riparian vegetation for up 

to 77 days (USFWS 2002). 

During dry periods, the CRLF is rarely found far from water, although it will sometimes 

disperse from its breeding habitat to forage and seek other suitable habitat under downed 

trees or logs, industrial debris, and agricultural features (UWFWS 2002). According to 

Jennings and Hayes (1994), CRLFs also use small mammal burrows and moist leaf litter 

as habitat. In addition, CRLFs may also use large cracks in the bottom of dried ponds as 

refugia; these cracks may provide moisture for individuals avoiding predation and solar 

exposure (Alvarez 2000). 

2.6 Designated Critical Habitat 

In a final rule published on April 13, 2006, 34 separate units of critical habitat were 

designated for the CRLF by USFWS (USFWS 2006; FR 51 19244-19346). A summary 

of the 34 critical habitat units relative to USFWS-designated recovery units and core 

areas (previously discussed in Section 2.5.1) is provided in Attachment I. 

‘Critical habitat’ is defined in the ESA as the geographic area occupied by the species at 

the time of the listing where the physical and biological features necessary for the 

conservation of the species exist, and there is a need for special management to protect 

the listed species. It may also include areas outside the occupied area at the time of 

listing if such areas are ‘essential to the conservation of the species.’ All designated 

critical habitat for the CRLF was occupied at the time of listing. Critical habitat receives 

protection under Section 7 of the ESA (Section 7) through prohibition against destruction 

or adverse modification with regard to actions carried out, funded, or authorized by a 

federal Agency. Section 7 requires consultation on federal actions that are likely to result 

in the destruction or adverse modification of critical habitat. 

To be included in a critical habitat designation, the habitat must be ‘essential to the 

conservation of the species.’ Critical habitat designations identify, to the extent known 

using the best scientific and commercial data available, habitat areas that provide 

essential life cycle needs of the species or areas that contain certain primary constituent 

elements (PCEs) (as defined in 50 CFR 414.12(b)). PCEs include, but are not limited to, 

space for individual and population growth and for normal behavior; food, water, air, 

light, minerals, or other nutritional or physiological requirements; cover or shelter; sites 

for breeding, reproduction, rearing (or development) of offspring; and habitats that are 

35
protected from disturbance or are representative of the historic geographical and 

ecological distributions of a species. The designated critical habitat areas for the CRLF 

are considered to have the following PCEs that justify critical habitat designation: 

• Breeding aquatic habitat; 

• Non-breeding aquatic habitat; 

• Upland habitat; and 

• Dispersal habitat. 

Further description of these habitat types is provided in Attachment I. 

Occupied habitat may be included in the critical habitat only if essential features within 

the habitat may require special management or protection. Therefore, USFWS does not 

include areas where existing management is sufficient to conserve the species. Critical 

habitat is designated outside the geographic area presently occupied by the species only 

when a designation limited to its present range would be inadequate to ensure the 

conservation of the species. For the CRLF, all designated critical habitat units contain all 

four of the PCEs, and were occupied by the CRLF at the time of FR listing notice in 

April 2006. The FR notice designating critical habitat for the CRLF includes a special 

rule exempting routine ranching activities associated with livestock ranching from 

incidental take prohibitions. The purpose of this exemption is to promote the 

conservation of rangelands, which could be beneficial to the CRLF, and to reduce the rate 

of conversion to other land uses that are incompatible with CRLF conservation. Please 

see Attachment I for a full explanation on this special rule. 

USFWS has established adverse modification standards for designated critical habitat 

(USFWS 2006). Activities that may destroy or adversely modify critical habitat are those 

that alter the PCEs and jeopardize the continued existence of the species. Evaluation of 

actions related to use of myclobutanil that may alter the PCEs of the CRLF’s critical 

habitat form the basis of the critical habitat impact analysis. According to USFWS 

(2006), activities that may affect critical habitat and therefore result in adverse effects to 

the CRLF include, but are not limited to the following: 

(1) Significant alteration of water chemistry or temperature to levels beyond the 

tolerances of the CRLF that result in direct or cumulative adverse effects to 

individuals and their life-cycles. 

(2) Alteration of chemical characteristics necessary for normal growth and viability 

of juvenile and adult CRLFs. 

(3) Significant increase in sediment deposition within the stream channel or pond or 

disturbance of upland foraging and dispersal habitat that could result in 

elimination or reduction of habitat necessary for the growth and reproduction of 

the CRLF by increasing the sediment deposition to levels that would adversely 

affect their ability to complete their life cycles. 

(4) Significant alteration of channel/pond morphology or geometry that may lead to 

changes to the hydrologic functioning of the stream or pond and alter the timing, 

duration, water flows, and levels that would degrade or eliminate the CRLF 

36
and/or its habitat. Such an effect could also lead to increased sedimentation and 

degradation in water quality to levels that are beyond the CRLF’s tolerances. 

(5) Elimination of upland foraging and/or aestivating habitat or dispersal habitat. 

(6) Introduction, spread, or augmentation of non-native aquatic species in stream 

segments or ponds used by the CRLF. 

(7) Alteration or elimination of the CRLF’s food sources or prey base (also 

evaluated as indirect effects to the CRLF). 

As previously noted in Section 2.1, the Agency believes that the analysis of direct and 

indirect effects to listed species provides the basis for an analysis of potential effects on 

the designated critical habitat. Because myclobutanil is expected to directly impact living 

organisms within the action area, critical habitat analysis for myclobutanil is limited in a 

practical sense to those PCEs of critical habitat that are biological or that can be 

reasonably linked to biologically mediated processes. 

2.7 Action Area 

For listed species assessment purposes, the action area is considered to be the area 

affected directly or indirectly by the federal action and not merely the immediate area 

involved in the action (50 CFR 402.02). It is recognized that the overall action area for 

the national registration of myclobutanil is likely to encompass considerable portions of 

the United States based on the large array of agricultural uses. However, the scope of this 

assessment limits consideration of the overall action area to those portions that may be 

applicable to the protection of the CRLF and its designated critical habitat within the state 

of California. The Agency’s approach to defining the action area under the provisions of 

the Overview Document (U.S. EPA 2004) considers the results of the risk assessment 

process to establish boundaries for that action area with the understanding that exposures 

below the Agency’s defined Levels of Concern (LOCs) constitute a no-effect threshold. 

For the purposes of this assessment, attention will be focused on the footprint of the 

action (i.e., the area where pesticide application occurs), plus all areas where offsite 

transport (i.e., spray drift, downstream dilution, etc.) may result in potential exposure 

within the state of California that exceeds the Agency’s LOCs. 

Deriving the geographical extent of this portion of the action area is based on 

consideration of the types of effects that myclobutanil may be expected to have on the 

environment, the exposure levels to myclobutanil that are associated with those effects, 

and the best available information concerning the use of myclobutanil and its fate and 

transport within the state of California. Specific measures of ecological effect that define 

the action area include any direct and indirect toxic effect and any potential effects to 

critical habitat, including reduction in survival, growth, and fecundity as well as the full 

suite of sublethal effects available in the effects literature. Therefore, the action area 

extends to a point where environmental exposures are below any measured lethal or 

sublethal effect threshold for any biological entity at the whole organism, organ, tissue, 

and cellular level of organization. In situations where it is not possible to determine the 

threshold for an observed effect, the action area is not spatially limited and is assumed to 

be the entire state of California. 

37
The definition of action area requires a stepwise approach that begins with an 

understanding of the federal action. The federal action is defined by the currently labeled 

uses for myclobutanil. An analysis of labeled uses and review of available product labels 

was completed. Several of the currently labeled uses are special local needs (SLN) uses 

or are restricted to specific states and are excluded from this assessment. In addition, a 

distinction has been made between food use crops and those that are non-food/nonagricultural uses. For those uses relevant to the CRLF, the analysis indicates that, for 

myclobutanil, the following agricultural uses are considered as part of the federal action 

evaluated in this assessment: 

• almond, apple, apricot, artichoke, asparagus, blackberry, boysenberry, canistel, 

carrot, cherry, cucurbit vegetables (e.g. melons, squash), currant, dewberry, 

eggplant, gooseberry, green beans, grapes, hops, lettuce, mango, mayhaw, 

nectarine, okra, papaya, peach, pepper, plum, prune, raspberry, sapodilla, 

strawberry, sugar beet, tomato, and youngberry. 

In addition, the following non-food and non-agricultural uses are considered: 

• commercial, residential and golf course turf, ornamental and herbaceous plants, 

grass grown for seed, cotton seed, ornamental sod farms, Douglas fir and loblolly 

pine and slash pine forests, and hybrid cotton wood/poplar plantations. 

Following a determination of the assessed uses, an evaluation of the potential “footprint” 

of myclobutanil use patterns (i.e., the area where pesticide application occurs) is 

determined. This “footprint” represents the initial area of concern, based on an analysis of 

available land cover data for the state of California. The initial area of concern is defined 

as all land cover types and the stream reaches within the land cover areas that represent 

the labeled uses described above. A map representing all the land cover types that make 

up the initial area of concern for myclobutanil is presented in Figure 2.6. 

The following land cover types were used for myclobutanil cultivated crops, forest, 

orchards and vineyards and turf. More information regarding which specific uses are 

represented for each land cover types can be found in Appendix E. 

38
 

Figure 2.6 Initial Area of Concern of “footprint” of potential use for myclobutanil 

39
As previously discussed, the action area is defined by the most sensitive measure of 

direct and indirect ecological toxic effects including reduction in survival, growth, 

reproduction, and the entire suite of sublethal effects from valid, peer-reviewed studies. 

Due to the lack of a defined dose at which there were no effects and the presence of 

sublethal effects (lethargy and anorexia) and mortalities at all dose levels in an avian 

acute oral toxicity study (MRID 00144286), the spatial extent of the action area (i.e., the 

boundary where exposures and potential effects are less than the Agency’s LOC) for 

myclobutanil cannot be determined. Therefore, it is assumed that the action area 

encompasses the entire state of California, regardless of the spatial extent (i.e., initial area 

of concern or footprint) of the pesticide use(s). 

2.8 Assessment Endpoints and Measures of Ecological Effect 

Assessment endpoints are defined as “explicit expressions of the actual environmental 

value that is to be protected.”1

 Selection of the assessment endpoints is based on valued 

entities (e.g., CRLF, organisms important in the life cycle of the CRLF, and the PCEs of 

its designated critical habitat), the ecosystems potentially at risk (e.g., waterbodies, 

riparian vegetation, and upland and dispersal habitats), the migration pathways of 

myclobutanil (e.g., runoff, spray drift, etc.), and the routes by which ecological receptors 

are exposed to myclobutanil (e.g., direct contact, etc.). 

2.8.1 Assessment Endpoints for the CRLF 

Assessment endpoints for the CRLF include direct toxic effects on the survival, 

reproduction, and growth of the CRLF, as well as indirect effects, such as reduction of 

the prey base or effects to its habitat. In addition, potential effects to critical habitat are 

assessed by evaluating potential effects to PCEs, which are components of the habitat 

areas that provide essential life cycle needs of the CRLF. Each assessment endpoint 

requires one or more “measures of ecological effect,” defined as changes in the attributes 

of an assessment endpoint or changes in a surrogate entity or attribute in response to 

exposure to a pesticide. Specific measures of ecological effect are generally evaluated 

based on acute and chronic toxicity information from registrant-submitted guideline tests 

that are performed on a limited number of organisms. Additional ecological effects data 

from the open literature are also considered. It should be noted that assessment endpoints 

are limited to direct and indirect effects associated with survival, growth, and fecundity, 

and do not include the full suite of sublethal effects used to define the action area. 

According the Overview Document (USEPA 2004), the Agency relies on acute and 

chronic effects endpoints that are either direct measures of impairment of survival, 

growth, or fecundity or endpoints for which there is a scientifically robust, peer reviewed 

relationship that can quantify the impact of the measured effect endpoint on the 

assessment endpoints of survival, growth, and fecundity. 

A complete discussion of all the toxicity data available for this risk assessment, including 

resulting measures of ecological effect selected for each taxonomic group of concern, is 

 

1

 U.S. EPA (1992). Framework for Ecological Risk Assessment. EPA/630/R-92/001. 

40
included in Section 4.0 of this document. A summary of the assessment endpoints and 

measures of ecological effect selected to characterize potential assessed direct and 

indirect CRLF risks associated with exposure to myclobutanil is provided in Table 2.4. 

Table 2.4 Assessment Endpoints and Measures of Ecological Effects 

Assessment Endpoint Measures of Ecological Effects2

Aquatic-Phase CRLF 

(Eggs, larvae, juveniles, and adults)a

Direct Effects 

1. Survival, growth, and reproduction of CRLF 1a. Bluegill sunfish acute LC50 

1b. Fathead minnow chronic NOAEC 

Indirect Effects and Critical Habitat Effects 

2. Survival, growth, and reproduction of CRLF 

individuals via indirect effects on aquatic prey food 

supply (i.e., fish, freshwater invertebrates, nonvascular plants) 

2a. Bluegill sunfish acute LC50, water flea acute 

LC50, green algae EC50. 

2b. Fathead minnow chronic NOAEC; no 

freshwater invertebrate chronic study available; 

daphnia chronic NOAEC from 9 similar conazole 

fungicides. 

3. Survival, growth, and reproduction of CRLF 

individuals via indirect effects on habitat, cover, 

food supply, and/or primary productivity (i.e.,

aquatic plant community) 

3a. No vascular plant study available; duckweed 

EC50 data from 7 similar conazole fungicides. 

3b. Green algae EC50. 

4. Survival, growth, and reproduction of CRLF 

individuals via effects to riparian vegetation 

4a. No seedling emergence or vegetative vigor 

studies available; terrestrial plant EC25 and NOAEC 

data from 5 similar conazole fungicides 

4b. No seedling emergence or vegetative vigor 

studies available; terrestrial plant EC25 and NOAEC 

data from 5 similar conazole fungicides 

Terrestrial-Phase CRLF 

(Juveniles and adults) 

Direct Effects 

5. Survival, growth, and reproduction of CRLF 

individuals via direct effects on terrestrial phase 

adults and juveniles 

5a. Bobwhite quail LD50 and Mallard duck LC50b 

5b. Bobwhite quail chronic NOAEC

Indirect Effects and Critical Habitat Effects 

6. Survival, growth, and reproduction of CRLF 

individuals via effects on terrestrial prey 

(i.e.,terrestrial invertebrates, small mammals , and 

frogs) 

6a. Honey bee acute EC50 and mouse acute LD50 

6b. Rat chronic NOAEC (no chronic invertebrate 

study available) 

7. Survival, growth, and reproduction of CRLF 

individuals via indirect effects on habitat (i.e.,

riparian and upland vegetation) 

7a. No seedling emergence or vegetative vigor 

studies available; terrestrial plant EC25 and NOAEC 

data from 5 similar conazole fungicides 

7b. No seedling emergence or vegetative vigor 

studies available; terrestrial plant EC25 and NOAEC 

data from 5 similar conazole fungicides a

 Adult frogs are no longer in the “aquatic phase” of the amphibian life cycle; however, submerged adult 

frogs are considered “aquatic” for the purposes of this assessment because exposure pathways in the water 

are considerably different that exposure pathways on land. 

b

 Birds are used as surrogates for terrestrial phase amphibians. 

 

2

 All registrant-submitted and open literature toxicity data reviewed for this assessment are included in 

Appendix A. 

41
2.8.2 Assessment Endpoints for Designated Critical Habitat 

As previously discussed, designated critical habitat is assessed to evaluate actions related 

to the use of myclobutanil that may alter the PCEs of the CRLF’s critical habitat. PCEs 

for the CRLF were previously described in Section 2.6. Actions that may modify critical 

habitat are those that alter the PCEs and jeopardize the continued existence of the CRLF. 

Therefore, these actions are identified as assessment endpoints. It should be noted that 

evaluation of PCEs as assessment endpoints is limited to those of a biological nature (i.e., 

the biological resource requirements for the listed species associated with the critical 

habitat) and those for which myclobutanil effects data are available. Effects to the 

critical habitat of the CRLF include, but are not limited to those listed in Section 2.6. 

Measures of such possible effects by labeled use of myclobutanil on critical habitat of the 

CRLF are described in Table 2.5. Some components of these PCEs are associated with 

physical abiotic features (e.g., presence and/or depth of a water body, or distance between 

two sites), which are not expected to be measurably altered by use of pesticides. 

Assessment endpoints used for the analysis of designated critical habitat are based on the 

adverse modification standard established by USFWS (2006). 

42
Table 2.5 Summary of Assessment Endpoints and Measures of Ecological Effect for 

Primary Constituent Elements of Designated Critical Habitata

Assessment Endpoint Measures of Ecological Effect 

Aquatic-Phase CRLF PCEs 

(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)

Alteration of channel/pond morphology or geometry 

and/or increase in sediment deposition within the 

stream channel or pond: aquatic habitat (including 

riparian vegetation) provides for shelter, foraging, 

predator avoidance, and aquatic dispersal for juvenile 

and adult CRLFs. 

a. Green algae EC50. No vascular plant study available; 

duckweed EC50 data from 7 similar conazole fungicides. 

b. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides 

c. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides 

Alteration in water chemistry/quality including 

temperature, turbidity, and oxygen content necessary 

for normal growth and viability of juvenile and adult 

CRLFs and their food source.

a. Green algae EC50. No vascular plant study available; 

duckweed EC50 data from 7 similar conazole fungicides. 

b. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides 

c. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides 

Alteration of other chemical characteristics necessary 

for normal growth and viability of CRLFs and their 

food source. 

a. Bluegill sunfish acute LC50 and water flea acute LC50. 

b. Fathead minnow chronic NOAEC. No freshwater 

invertebrate chronic study available; daphnia chronic 

NOAEC from 9 similar conazole fungicides.

Reduction and/or modification of aquatic-based food 

sources for pre-metamorphs (e.g., algae) 

a. Green algae EC50. No vascular plant study available; 

duckweed EC50 data from 7 similar conazole fungicides. 

Terrestrial-Phase CRLF PCEs 

(Upland Habitat and Dispersal Habitat)

Elimination and/or disturbance of upland habitat; 

ability of habitat to support food source of CRLFs: 

Upland areas within 200 ft of the edge of the riparian 

vegetation or dripline surrounding aquatic and riparian 

habitat that are comprised of grasslands, woodlands, 

and/or wetland/riparian plant species that provides the 

CRLF shelter, forage, and predator avoidance 

Elimination and/or disturbance of dispersal habitat: 

Upland or riparian dispersal habitat within designated 

units and between occupied locations within 0.7 mi of 

each other that allow for movement between sites 

including both natural and altered sites which do not 

contain barriers to dispersal 

Reduction and/or modification of food sources for 

terrestrial phase juveniles and adults 

Alteration of chemical characteristics necessary for 

normal growth and viability of juvenile and adult 

CRLFs and their food source. 

a. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides. 

b. No seedling emergence or vegetative vigor studies 

available; terrestrial plant EC25 and NOAEC data from 5 

similar conazole fungicides. 

c. Bobwhite quail LD50, mallard duck LC50, bobwhite quail 

chronic NOAEC, honey bee acute EC50, mouse acute LD50, 

rat chronic NOAEC (no chronic invertebrate study 

available), bluegill sunfish acute LC50 and fathead minnow 

chronic NOAEC. 

a Physico-chemical water quality parameters such as salinity, pH, and hardness are not evaluated because these processes are not 

biologically mediated and, therefore, are not relevant to the endpoints included in this assessment.

43
2.9 Conceptual Model 

2.9.1 Risk Hypotheses 

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in 

assessment endpoints) and may be based on theory and logic, empirical data, 

mathematical models, or probability models (U.S. EPA, 1998). For this assessment, the 

risk is stressor-linked, where the stressor is the release of myclobutanil to the 

environment. The following risk hypotheses are presumed for this endangered species 

assessment: 

The labeled use of myclobutanil within the action area may: 

• directly affect the CRLF by causing mortality or by adversely affecting growth or 

fecundity; 

• indirectly affect the CRLF by reducing or changing the composition of food 

supply; 

• indirectly affect the CRLF or affect designated critical habitat by reducing or 

changing the composition of the aquatic plant community in the ponds and 

streams comprising the species’ current range and designated critical habitat, thus 

affecting primary productivity and/or cover; 

• indirectly affect the CRLF or affect designated critical habitat by reducing or 

changing the composition of the terrestrial plant community (i.e., riparian habitat) 

required to maintain acceptable water quality and habitat in the ponds and streams 

comprising the species’ current range and designated critical habitat; 

• affect the designated critical habitat of the CRLF by reducing or changing 

breeding and non-breeding aquatic habitat (via modification of water quality 

parameters, habitat morphology, and/or sedimentation); 

• affect the designated critical habitat of the CRLF by reducing the food supply 

required for normal growth and viability of juvenile and adult CRLFs; 

• affect the designated critical habitat of the CRLF by reducing or changing upland 

habitat within 200 ft of the edge of the riparian vegetation necessary for shelter, 

foraging, and predator avoidance; 

• affect the designated critical habitat of the CRLF by reducing or changing 

dispersal habitat within designated units and between occupied locations within 

0.7 mi of each other that allow for movement between sites including both natural 

and altered sites which do not contain barriers to dispersal; 

• affect the designated critical habitat of the CRLF by altering chemical 

characteristics necessary for normal growth and viability of juvenile and adult 

CRLFs. 

2.9.2 Diagram 

The conceptual model is a graphic representation of the structure of the risk assessment. 

It specifies the stressor (myclobutanil) release mechanisms, biological receptor types, and 

44
effects endpoints of potential concern. The conceptual models for terrestrial and aquatic 

exposures are shown in Figure 2.7 and Figure 2.8, respectively, which include the 

conceptual models for the aquatic and terrestrial PCE components of critical habitat. 

Exposure routes shown in dashed lines are not quantitatively considered because the 

contribution of those potential exposure routes to potential effects on the CRLF and 

designated critical habitat is expected to be negligible. 

Stressor 

Source 

Receptors 

Attribute 

Change 

Myclobutanil applied to use site 

Direct 

application Spray drift

Birds/terrestrialphase amphibians/ 

reptiles/mammals 

Terrestrial 

insects 

Individual 

organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain

Reduction in prey 

Modification of PCEs 

related to prey availability 

Habitat integrity 

Reduction in primary productivity

Reduced cover 

Community change 

Modification of PCEs related to 

habitat 

Terrestrial/riparian plants

grasses/forbs, fruit, seeds 

(trees, shrubs) 

Runoff 

Mammals/

birds 

Exposure 

Media 

Soil

Ingestion 

Ingestion

Ingestion 

Ingestion

Dermal uptake/Ingestion

Long range 

atmospheric 

transport 

Root uptake 

Wet/dry deposition 

Terrestrial-phase 

amphibians 

Ingestion 

Figure 2.7 Conceptual Model for Myclobutanil Effects on Terrestrial Phase of the 

CRLF 

45
Myclobutanil applied to use site Stressor

Source 

Receptors

Attribute 

Change 

** Route of exposure includes only ingestion of aquatic fish and invertebrates 

Spray drift 

Fish/aquatic-phase 

amphibians 

Exposure 

Media 

**Piscivorous mammals 

 and birds 

Individual 

organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain

Reduction in algae 

Reduction in prey 

Modification of PCEs 

 related to prey availability 

Habitat integrity 

Reduction in primary 

productivity

Reduced cover 

Community change 

Modification of PCEs related to 

 habitat 

Surface water/ 

Sediment 

Runoff

Aquatic Animals

Invertebrates 

Vertebrates 

Uptake/gills 

or integument 

Ingestion Ingestion

Uptake/gills 

or integument 

Aquatic Plants

Non-vascular 

Vascular

Uptake/cell, 

roots, leaves Riparian plants

terrestrial 

exposure 

pathways see 

Figure 2.7 

Long range 

atmospheric 

transport 

Wet/dry deposition 

Soil Groundwater

Figure 2.8 Conceptual Model for Myclobutanil Effects on Aquatic Phase of the 

CRLF 

2.10 Analysis Plan 

In order to address the risk hypothesis, the potential for direct and indirect effects to the 

CRLF, its prey, and its habitat is estimated. In the following sections, the use, 

environmental fate, and ecological effects of myclobutanil are characterized and 

integrated to assess the risks. This is accomplished using a risk quotient (ratio of 

exposure concentration to effects concentration) approach. Although risk is often defined 

as the likelihood and magnitude of adverse ecological effects, the risk quotient-based 

approach does not provide a quantitative estimate of likelihood and/or magnitude of an 

adverse effect. However, as outlined in the Overview Document (U.S. EPA, 2004), the 

likelihood of effects to individual organisms from particular uses of myclobutanil is 

estimated using the probit dose-response slope and either the level of concern (discussed 

below) or actual calculated risk quotient value. 

46
2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 

2.10.1.1 Measures of Exposure 

The environmental fate properties of myclobutanil and the degradation product 1,2,4-

triazole along with available monitoring data indicate that for myclobutanil runoff and 

spray drift are the principle potential transport mechanisms and for 1,2,4-triazole runoff 

and erosion are the principle potential transport mechanisms to the aquatic and terrestrial 

habitats of the CRLF. Monitoring data have also detected myclobutanil in rain water, 

thus secondary deposition is also a potential route of exposure but is expected to be 

minor. In this assessment, transport of myclobutanil and myclobutanil plus 1,2,4-triazole 

through runoff and spray drift is considered in deriving quantitative estimates of 

myclobutanil exposure to CRLF, its prey and its habitats. 

Measures of exposure are based on aquatic and terrestrial models that predict estimated 

environmental concentrations (EECs) of myclobutanil using maximum labeled 

application rates and methods of application. The models used to predict aquatic EECs 

are the Pesticide Root Zone Model coupled with the Exposure Analysis Model System 

(PRZM/EXAMS). The model used to predict terrestrial EECs on food items is T-REX. 

The model used to derive EECs relevant to terrestrial and wetland plants is TerrPlant. 

These models are parameterized using relevant reviewed registrant-submitted 

environmental fate data. 

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are screening 

simulation models coupled with the input shell pe5.pl (Aug 2007) to generate daily 

exposures and 1-in-10 year EECs of myclobutanil and myclobutanil plus 1,2,4-triazole 

that may occur in surface water bodies adjacent to application sites receiving 

myclobutanil through runoff and spray drift. PRZM simulates pesticide application, 

movement and transformation on an agricultural field and the resultant pesticide loadings 

to a receiving water body via runoff, erosion and spray drift. EXAMS simulates the fate 

of the pesticide and resulting concentrations in the water body. The standard scenario 

used for ecological pesticide assessments assumes application to a 10-hectare agricultural 

field that drains into an adjacent 1-hectare water body, 2-meters deep (20,000 m3

 volume) 

with no outlet. PRZM/EXAMS was used to estimate screening-level exposure of aquatic 

organisms to myclobutanil and myclobutanil plus 1,2,4-triazole. The measure of 

exposure for aquatic species is the 1-in-10 year return peak or rolling mean concentration. 

The 1-in-10 year peak is used for estimating acute exposures of direct effects to the 

CRLF, as well as indirect effects to the CRLF through effects to potential prey items, 

including: algae, aquatic invertebrates, fish and frogs. The 1-in-10-year 60-day mean is 

used for assessing chronic exposure to the CRLF and fish and frogs serving as prey 

items; the 1-in-10-year 21-day mean is used for assessing chronic exposure for aquatic 

invertebrates, which are also potential prey items. 

Exposure estimates for the terrestrial-phase CRLF and terrestrial invertebrates and 

mammals (serving as potential prey) assumed to be in the target area or in an area 

exposed to spray drift are derived using the T-REX model (version 1.4.1, 10/09/2008). 

47
This model incorporates the Kenega nomograph, as modified by Fletcher et al. (1994), 

which is based on a large set of actual field residue data. The upper limit values from the 

nomograph represented the 95th percentile of residue values from actual field 

measurements (Hoerger and Kenega, 1972). For modeling purposes, direct exposures of 

the CRLF to myclobutanil through contaminated food are estimated using the EECs for 

the small bird (20 g) which consumes small insects. Dietary-based and dose-based 

exposures of potential prey (small mammals) are assessed using the small mammal (15 g) 

which consumes short grass. The small bird (20g) consuming small insects and the small 

mammal (15g) consuming short grass are used because these categories represent the 

largest RQs of the size and dietary categories in T-REX that are appropriate surrogates 

for the CRLF and one of its prey items. Estimated exposures of terrestrial insects to 

myclobutanil are bound by using the dietary based EECs for small insects and large 

insects. For granular applications, an LD50 per square foot is estimated based on 

application rate and toxicity. 

Birds are currently used as surrogates for terrestrial-phase CRLF. However, amphibians 

are poikilotherms (body temperature varies with environmental temperature) while birds 

are homeotherms (temperature is regulated, constant, and largely independent of 

environmental temperatures). Therefore, amphibians tend to have much lower metabolic 

rates and lower caloric intake requirements than birds or mammals. As a consequence, 

birds are likely to consume more food than amphibians on a daily dietary intake basis, 

assuming similar caloric content of the food items. Therefore, the use of avian food 

intake allometric equation as a surrogate to amphibians is likely to result in an overestimation of exposure and risk for reptiles and terrestrial-phase amphibians. Therefore, 

T-REX (version 1.4.1) has been refined to the T-HERPS model (v. 1.0), which allows for 

an estimation of food intake for poikilotherms using the same basic procedure as T-REX 

to estimate avian food intake. 

EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant 

(version 1.2.2, 12/26/2006). This model uses estimates of pesticides in runoff and in 

spray drift to calculate EECs. EECs are based upon solubility, application rate and 

minimum incorporation depth. 

The spray drift model, AgDRIFT is used to assess exposures of terrestrial phase CRLF 

and its prey to myclobutanil deposited on terrestrial habitats by spray drift. In addition to 

the buffered area from the spray drift analysis, the downstream extent of myclobutanil 

that exceeds the LOC for the effects determination is also considered. 

2.10.1.2 Measures of Effect 

Data identified in Section 2.8 are used as measures of effect for direct and indirect effects 

to the CRLF. Data were obtained from registrant submitted studies or from literature 

studies identified by ECOTOX. The ECOTOXicology database (ECOTOX) was searched 

in order to provide more ecological effects data and in an attempt to bridge existing data 

gaps. ECOTOX is a source for locating single chemical toxicity data for aquatic life, 

48
terrestrial plants, and wildlife. ECOTOX was created and is maintained by the USEPA, 

Office of Research and Development, and the National Health and Environmental Effects 

Research Laboratory's Mid-Continent Ecology Division. 

The assessment of risk for direct effects to the terrestrial-phase CRLF makes the 

assumption that toxicity of myclobutanil to birds is similar to or less than the toxicity to 

the terrestrial-phase CRLF. The same assumption is made for fish and aquatic-phase 

CRLF. Algae, aquatic invertebrates, fish, and amphibians represent potential prey of the 

CRLF in the aquatic habitat. Terrestrial invertebrates, small mammals, and terrestrialphase amphibians represent potential prey of the CRLF in the terrestrial habitat. Aquatic, 

semi-aquatic, and terrestrial plants represent habitat of CRLF. 

The ecotoxicity database for myclobutanil is not complete. Acceptable data are not 

available, either submitted or in the open literature for chronic toxicity to aquatic 

freshwater invertebrates, aquatic vascular plants and terrestrial plants. For the purpose of 

risk description in this assessment, toxicity data from other triazole sterol 14αdemethylase-inhibitors (DMIs) for these particular studies were utilized. 

The acute measures of effect used for animals in this screening level assessment are the 

LD50, LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, 

given all at once, that is estimated to cause the death of 50% of the test organisms. LC 

stands for “Lethal Concentration” and LC50 is the concentration of a chemical that is 

estimated to kill 50% of the test organisms. EC stands for “Effective Concentration” and 

the EC50 is the concentration of a chemical that is estimated to produce a specific effect in 

50% of the test organisms. Endpoints for chronic measures of exposure for listed and 

non-listed animals are the NOAEL/NOAEC and NOEC. NOAEL stands for “No 

Observed-Adverse-Effect-Level” and refers to the highest tested dose of a substance that 

has been reported to have no harmful (adverse) effects on test organisms. The NOAEC 

(i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test concentration at 

which none of the observed effects were statistically different from the control. The 

NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute 

exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants). 

It is important to note that the measures of effect for direct and indirect effects to the 

CRLF and its designated critical habitat are associated with impacts to survival, growth, 

and fecundity, and do not include the full suite of sublethal effects used to define the 

action area. According the Overview Document (USEPA 2004), the Agency relies on 

effects endpoints that are either direct measures of impairment of survival, growth, or 

fecundity or endpoints for which there is a scientifically robust, peer reviewed 

relationship that can quantify the impact of the measured effect endpoint on the 

assessment endpoints of survival, growth, and fecundity. 

49
2.10.1.3 Integration of Exposure and Effects 

Risk characterization is the integration of exposure and ecological effects characterization 

to determine the potential ecological risk from agricultural and non-agricultural uses of 

myclobutanil, and the likelihood of direct and indirect effects to CRLF in aquatic and 

terrestrial habitats. The exposure and toxicity effects data are integrated in order to 

evaluate the risks of adverse ecological effects on non-target species. For the assessment 

of myclobutanil risks, the risk quotient (RQ) method is used to compare exposure and 

measured toxicity values. EECs are divided by acute and chronic toxicity values. The 

resulting RQs are then compared to the Agency’s levels of concern (LOCs) (USEPA, 

2004) (see Appendix F). 

For this endangered species assessment, listed species LOCs are used for comparing RQ 

values for acute and chronic exposures of myclobutanil directly to the CRLF. If 

estimated exposures directly to the CRLF of myclobutanil resulting from a particular use 

are sufficient to exceed the listed species LOC, then the effects determination for that use 

is “may affect”. When considering indirect effects to the CRLF due to effects to animal 

prey (aquatic and terrestrial invertebrates, fish, frogs, and mice), the listed species LOCs 

are also used. If estimated exposures to CRLF prey of myclobutanil resulting from a 

particular use are sufficient to exceed the listed species LOC, then the effects 

determination for that use is a “may affect.” If the RQ being considered also exceeds the 

non-listed species acute risk LOC, then the effects determination is a LAA. If the acute 

RQ is between the listed species LOC and the non-listed acute risk species LOC, then 

further lines of evidence (i.e. probability of individual effects, species sensitivity 

distributions) are considered in distinguishing between a determination of NLAA and a 

LAA. When considering indirect effects to the CRLF due to effects to algae as dietary 

items or plants as habitat, the non-listed species LOC for plants is used because the CRLF 

does not have an obligate relationship with any particular aquatic and/or terrestrial plant. 

If the RQ being considered for a particular use exceeds the non-listed species LOC for 

plants, the effects determination is “may affect”. Further information on LOCs is 

provided in Appendix F. 

2.10.1.4 Data Gaps 

Fate 

Data characterizing the environmental fate of myclobutanil and its degradation products 

is limited. The data was inadequate to determine the rate of formation and decline of the 

1,2,4-triazole degradation product. Models currently used by EFED assume that the 

degradation follow first order kinetics, and therefore require an estimate of the half-life. 

Myclobutanil degradation, however, is best described using a hockey stick degradation 

pattern. This type of degradation pattern cannot be modeled using first-order kinetics. 

The previously reported half-lives for myclobutanil range between 61 and 71 days, which 

described the decline reasonably well for the first 90 days of the study, but grossly 

overestimates the remaining decline. The method used to estimate these half-lives was 

50
not stated, but it appears that only the first 90 (or less) days of a 367 day study were used. 

EFED re-evaluated the data and re-estimated the decline rate constants utilizing all the 

data for myclobutanil (see discussion in Appendix C, Tables 2 and 3). 

The linear regression of the log-normal transformed myclobutanil radioactivity provided 

the best estimate of the measured residues (as percent of applied radioactivity) versus 

time (e.g., 29 to 33% myclobutanil) remaining at 367 days. The study was not conducted 

long enough to observe a DT75 or DT90. The 90-percent upper bound of the mean (n=2) 

aerobic soil metabolism half-life for myclobutanil was estimated to be 251 days. 

Analysis of the Freundlich Kads indicates sorption is not significantly correlated with 

organic matter (carbon). Therefore, lowest non-sand Freundlich Kads was used to 

estimate the EDWCs for myclobutanil (USEPA, 2002). 

Because there are no aerobic aquatic metabolism data, half-life was assumed to be twice 

that of the aerobic soil metabolism half-life estimated as a model input (USEPA, 2002). 

The anaerobic metabolism was assumed to be stable. 

Ecotoxicity 

No toxicity data are available for freshwater invertebrates (chronic exposure), aquatic 

vascular plants, and terrestrial plants. Qualitative assessments were conducted with data 

from similar DMI triazole fungicides, information from the open literature, and incident 

data. 

3 Exposure Assessment 

Myclobutanil is formulated as a dust, emulsifiable concentrate, granular, liquid, water 

dispersible granules (dry flowable), pressurized liquid, ready to use liquid, and wettable 

powder. Application equipment includes ground application, aerial application, 

chemigation, high and low volume spray, hand held, pressurized and pump up sprayers, 

moveable and solid set irrigation, and broadcast spreaders for granular applications. 

Risks from ground boom and aerial applications are expected to result in the highest offtarget levels of myclobutanil due to generally higher spray drift levels. Ground boom and 

aerial modes of application tend to use lower volumes of application applied in finer 

sprays than applications coincident with sprayers and spreaders and thus have a higher 

potential for off-target movement via spray drift. 

3.1 Label Application Rates and Intervals 

Myclobutanil labels may be categorized into two types: labels for manufacturing uses 

(including technical grade myclobutanil and its formulated products) and end-use 

products. While technical products, which contain myclobutanil of high purity, are not 

used directly in the environment, they are used to make formulated products, which can 

be applied in specific areas to control brown patch, black spot, rust, powdery mildew, 

blights, scab, mold, and leaf spot. The formulated product labels legally limit 

myclobutanil’s potential use to only those sites that are specified on the labels. 

51
Currently registered agricultural and non-agricultural uses of myclobutanil within 

California included in this assessment are shown in Table 2.2. 

3.2 Aquatic Exposure Assessment 

3.2.1 Modeling Approach 

Aquatic exposures are quantitatively estimated for all of assessed uses using scenarios 

that represent high exposure sites for myclobutanil use. Each of these sites represents a 

10 hectare field that drains into a 1-hectare pond that is 2 meters deep and has no outlet. 

Exposure estimates generated using the standard pond are intended to represent a wide 

variety of vulnerable water bodies that occur at the top of watersheds including prairie 

pot holes, playa lakes, wetlands, vernal pools, man-made and natural ponds, and 

intermittent and first-order streams. As a group, there are factors that make these water 

bodies more or less vulnerable than the standard surrogate pond. Static water bodies that 

have larger ratios of drainage area to water body volume would be expected to have 

higher peak EECs than the standard pond. These water bodies will be either shallower or 

have large drainage areas (or both). Shallow water bodies tend to have limited additional 

storage capacity, and thus, tend to overflow and carry pesticide in the discharge whereas 

the standard pond has no discharge. As watershed size increases beyond 10 hectares, at 

some point, it becomes unlikely that the entire watershed is planted to a single crop, 

which is all treated with the pesticide. Headwater streams can also have peak 

concentrations higher than the standard pond, but they tend to persist for only short 

periods of time and are then carried downstream. 

Crop-specific management practices for all of the assessed uses of myclobutanil were 

used for modeling, including application rates, number of applications per year, 

application intervals, and the first application date for each crop. The date of first 

application was developed based on several sources of information including data 

provided by BEAD, a summary of individual applications from the CDPR PUR data, and 

Crop Profiles maintained by the USDA. For example, the first applications of 

myclobutanil reported in the CDPR PUR database occurred in late February or early 

March and continued through mid-August, during the years 2001 to 2005. For grapes, 

the heaviest period of application began in April. Precipitation also tends to be greater in 

late winter and early spring then in the summer. Based upon the dates selected for crop 

emergence and harvest in the standard PRZM CA Grape scenario and the CDPR PUR 

data, the date selected for first application of myclobutanil for modeling was April 1 in 

(Figure 3.1). 

. 

52
0

50

100

150

200

250

300

350

3/1/01

3/8/01

3/15/01

3/22/01

3/29/01

4/5/01

4/12/01

4/19/01

4/26/01

5/3/01

5/10/01

5/17/01

5/24/01

5/31/01

6/7/01

6/14/01

6/21/01

6/28/01

7/5/01

7/12/01

7/19/01

7/26/01

Date of Application

Pounds Myclobutanil Applied

Figure 3.1 Summary of Applications (pounds versus date) of Myclobutanil to 

Grapes in 2001 from CDPR PUR Data. 

More detail on the crop profiles and the previous assessments may be found at: 

http://pestdata.ncsu.edu/cropprofiles/cropprofiles.cfm

3.2.2 PRZM Scenarios 

PRZM scenarios used to model aquatic exposures resulting from applications of specific 

uses are identified in Tables 3.5 and 3.6. In cases where a scenario does not exist for a 

specific use, it is necessary to assign a surrogate scenario. Those surrogates are assigned 

to be most representative of the use being considered. Factors considered in the selection 

of scenarios include the similarity of crop growth and morphology, soils, product use and 

cropping area. Particular attention is given to the areas where the crops are grown 

because rainfall is understood to be a driving variable in PRZM modeling. Justifications 

for assignments of surrogates are defined below. All scenarios were parameterized for 

irrigation. 

Almond scenario (CA Almond STD) 

This scenario is intended to represent almond and walnut production in CA and is 

therefore, directly relevant to this use. The only crop using this scenario in this 

assessment was almonds. 

53
Citrus scenario (CA Citrus STD) 

This scenario is intended to represent applications of pesticides to oranges, grapefruit, 

kumquats, lemons, limes, tangelos, and tangerines in CA and is therefore, directly 

relevant to this use. The crops modeled with this scenario were mangoes, papaya, 

sapodilla, and white sapote. 

Cotton scenario (CA Cotton STD) 

This scenario is intended to represent applications of pesticides to cotton in CA and is 

therefore, directly relevant to this use. This scenario was used for cotton seed. 

Forestry Scenario (CA Forestry)

This scenario is intended to represent forestlands in northern California. The area of 

interest (AOI) includes Trinity, Shasta, Modoc, and Humboldt counties since they are 

predominantly forested and comprise the largest amount of pesticide application to forest 

lands in California. Based on typical forest composition and common pest species, this 

scenario is intended to represent coniferous evergreen forests. This scenario was used to 

represent Douglas Fir (seed orchard, forest, and shelter belt), loblolly pine forests, and 

hybrid cottonwood and poplar plantations, slash pine (forest), and ornamental and/or 

shade trees. 

Fruit scenario (CA Fruit STD)

The CA fruit scenario represents an orchard in Fresno County, which is located in the 

Central Valley. This scenario is intended to represent non-citrus fruit, including apples, 

crabapples, pears, quince, apricots, sweet and sour cherries, nectarines, peaches, plums, 

and prunes. Crops modeled using this scenario were apples, apricot, canistel, cherry, 

mamey (mamme apple), and mayhaw (hawthorn), nectarines, peaches, plums, and 

prunes. 

Grape Scenario (CA Grapes with Irrigation STD)

The CA grape scenario represents a vineyard located in Southern San Joaquin Valley. 

According to the 1997 Census of Agriculture, California is the major producer of table, 

wine, and raisin grapes with 85 percent of California’s production in the San Joaquin 

Valley and the bulk of the remainder in the Coachella Valley. This scenario was used to 

model grapes. 

Wine grapes scenario (CA Wine Grapes) 

This scenario is intended to represent applications of pesticides to grapes used for wine 

production in CA and is therefore, directly relevant to this use. Crops considered with this 

54
scenario included blackberry, boysenberry, currant, dewberry, gooseberry, raspberry, and 

youngberry. 

Hops Scenario (OR Hop STD)

This scenario, developed based on a hops vineyard in the Pacific Northwest, represents a 

vineyard located north of the area where hops are grown in CA Since the locations 

where hops are grown in CA are mostly in the northern part of the state, this scenario was 

deemed appropriate for modeling hops grown in CA. This scenario was used to represent 

hops. 

Lettuce Scenario (CA Lettuce STD)

A major leaf lettuce production area is the Coastal Valley of California. Since lettuce 

(Lectuca sativa) is predominantly grown on the West Coast, this scenario is used to 

represent lettuce production nationally. It is thus also suitable for representing lettuce 

culture in California and would be expected to be more vulnerable than most places in the 

state that grow lettuce and could impact the habitat of the red-legged frog. This scenario 

was used for both head and leaf lettuce. 

Melon scenario (CA Melon) 

This scenario is intended to represent applications of pesticides to cantaloupes, 

cucumbers, melons, pumpkins, watermelons, winter and summer squash in CA and is 

therefore, directly relevant to this use. This scenario was used to represent cantaloupes, 

casaba, cucumber, cucurbit vegetables, melons, squash, and watermelons. 

Mint Scenario (OR Mint STD)

According to NASS data, mint (grown for oil) has been grown in Lassen, Shasta and 

Siskiyou Counties. These counties are located in northern CA, bordering OR. Although 

this scenario represents a field located north of the area where mint is grown in CA, it 

was developed based on a mint field in the Pacific Northwest. Since the locations where 

mint is grown in CA are in the northern part of the state, this scenario was deemed 

appropriate for modeling mint grown in CA. This scenario was used to represent 

spearmint and peppermint crops. 

Nursery scenario (CA Nursery STD) 

This scenario is intended to represent applications of pesticides in outdoor nurseries in 

CA and is therefore, directly relevant to this use. Uses considered with this scenario 

included garland, chrysanthemum, ornamental ground cover, ornamental herbaceous 

plants, ornamental and non-flowering plants, ornamental woody shrubs and vines. 

55
Row crop scenario (CA Row Crop) 

This scenario is intended to represent production of carrots, beans, peppers and other 

crops in CA, and is therefore, directly relevant to these uses. Crops considered with this 

scenario included artichokes, asparagus, beans, carrots, pepper, and pimento. 

Strawberry scenario (CA Strawberry no plastic)

This scenario is intended to represent applications of pesticides to strawberries, nontarped, in CA. While the majority of strawberry growers use tarps, this scenario is 

considered a conservative approach and is therefore, is used for strawberries. 

Sugar beet scenario (CA Sugar beet OP)

This scenario was intend to represent applications of pesticides to sugar beets in CA, and 

is therefore, relevant to this use. This scenario was used to represent sugar beets. 

Tomato scenario (CA Tomato STD) 

This scenario is intended to represent applications of pesticides to tomatoes in CA and is 

therefore, directly relevant to this use. This scenario was used to represent eggplant, 

okra, and tomato crops. 

Turf scenario (CA Turf) 

This scenario is intended to represent applications of pesticides to sod farms, parks, 

recreational fields, grass for seed, and golf courses in CA and is therefore, directly 

relevant to this use. This scenario was used to represent Bluegrass, commercial and 

industrial lawns, golf-course turf, grasses grown for seed, ornamental lawns, residential 

lawns, sod farms, and turf. 

3.2.3 Model Inputs 

Myclobutanil is a fungicide used on a wide variety of food and non-food crops. 

Myclobutanil and selected myclobutanil plus 1,2,4-triazole environmental fate data used 

for generating model parameters is listed in Table 2.1. The input parameters used for 

PRZM and EXAMS models to estimate myclobutanil and myclobutanil plus 1,2,4-

triazole are summarized in Table 3.1. Residues in surface water were estimated for 

myclobutanil (parent) and for myclobutanil plus 1,2,4-triazole. The number of 

applications and the reapplication intervals for each crop modeled are listed in Tables 3.5 

and 3.6 and Appendix B (Tables 2 and 3). 

56
Table 3.1 Summary of PRZM and EXAMS Environmental Fate Data Used for 

Aquatic Exposure Inputs for Myclobutanil and Myclobutanil plus 1,2,4-triazole for 

Endangered Species Assessment for the CRLF 1

Parameter Input Value and Unit Rational 

Molecular Weight 288.8 g/ mola,b

Solubility 142 ppm @ 25 oCa,b

Aquatic Photolysis (t1/2) 0 days (Stable) No Data 

Soil Partition 

Coefficient, Freundlich 

Kads

Myclobutanil: 2.39 mg/La

1,2,4-triazole: 0.719 mg/Lb

Lowest non-sand value 

Lowest non-sand value 

Solubility in water (pH 

7, 25o

C) 

1420 mg/L (142 mg/L * 10)a,b EFED, Guidance 

USEPA, 2002 

Vapor Pressure 1.49 x 10-06 mm Hg at 25 oCa 

Henry’s Law Constant 3.25 x 10-09 atm m3/mole @ 25 oC 

Hydrolysis 0 days (Stable) 

Aerobic Soil 

Metabolism (t1/2) 

Myclobutanil: 251 daysa

Myclobutanil + 1,2,4-triazol: 315 daysb

Upper 90th bound on 

mean 

0nly 1 value 

Aerobic Aquatic 

Metabolism (t1/2) 

Myclobutanil 

Estimated as 502 daysa

Myclobutanil + 1,2,4-triazole

Estimated as 630 daysb

2 x ASM 

2 x ASM per USEPA, 

2002 

 Application Efficiency 

(APPEFF) 

0.95 aerial spray 

0.99 ground spray 

1.00 granular

EFED Guidance 

USEPA, 2002 

Drift (DRFT) 

Aerial Spray 

Aerial (0.05 Drift) 

Ground (0.01Drift) 

Granular (0.00) 

EFED Guidance 

USEPA, 2002 

Chemical Application 

Method (CAM) 

2 - foliar 

1 – granular 

5 – cotton seed (incorporation depth 3 

cm) 

Label 

1

 – Inputs determined in accordance with EFED “Guidance for Chemistry and Management Practice Input 

Parameters for Use in Modeling the Environmental Fate and Transport of Pesticides” dated February 28, 

2002 

a – Value used to estimate myclobutanil EECs. 

b

 – Value used to estimate myclobutanil plus 1,2,4-triazole EECs 

The myclobutanil plus 1,2,4-triazole EECs were estimated by using the half-life 

estimated from the decline of the sum of myclobutanil and 1,2,4-triazole with time using 

assuming first-order kinetics (Appendix C. Environmental Fate Data) and assuming the 

greater mobility (Freundlich Kads) of the 1,2,4-triazole (Table 3.1). 

The myclobutanil was assumed to be applied by ground and aerial spray methods as a 

foliar, and broadcast as a granular. The other methods of application include chemigation, 

57
sprinkler irrigation, and hand sprayers. The application rates were obtained from the 

labels. The maximum number of applications, the maximum single application rate, and 

maximum total application rate per crop cycle or year, and minimum reapplication 

interval were used when possible. When the number of applications times the maximum 

single rate exceeded the labels total maximum rate per crop cycle (cc) or yearly rate, the 

last application was reduced so as not to exceed the total amount. Several uses (i.e., 

nectarines) did not have enough applications (0.15 lb ai/A/application x 7 applications = 

1.05 lb ai/A/cc with a maximum per cc of 1.305 lb ai/A) to obtain the total maximum 

crop cycle or year rate. Eight applications at 0.15 lb ai/A/application + 1 application of 

0.105 lb ai/A would be required. 

3.2.4 Available Monitoring Data 

3.2.4.1 Aquatic Exposure Monitoring and Field Data 

Monitoring studies which included myclobutanil as an analyte were the USGS NAWQA 

(USGS, 1991) and the Reservoir Pilot Monitoring Program (USGS, 2001). Myclobutanil 

is not included in the CDPR monitoring program. These monitoring studies, which are 

discussed in further detail below, were not specifically targeted to myclobutanil use areas. 

The 1,2,4-triazole degradate was not included in the analysis. 

Reservoir Pilot Monitoring Program (USGS, 2001) 

Myclobutanil was included in a study that monitored a number of water supply reservoirs 

and finished water (USGS, 2001). Residues were detected at low concentrations in about 

1 percent of 317 samples of raw water, with no detections in the finished water (Table 

3.2). The degradation products were not included. 

Table 3.2 Myclobutanil results from the summary of analysis of moderate-use 

pesticides and degradates in water samples from water supply intakes and finishedsupply taps in Reservoir Pilot Monitoring Program. (USGS, 2001) 

No. of 

Samples 

No. of Detections 

(Quantifiable No. 

of Detections) 

Frequency of 

Detection 

(%) 

Maximum 

Detection 

(μg/L) 

Method 

Reporting 

Level 

(μg/L) 

Raw Water 317 3 (2) 0.9 0.015 0.008 

Finished Water 221 0 0 0 0.008 

USGS NAWQA (National Water Quality Assessment Program) 

The USGS NAWQA data was downed load on 05/13/09 

(http://infotrek.er.usgs.gov/traverse/f?p=NAWQA:HOME:3748645897450568) 

 and “contained data through water year 2007”. 

58
Surface Water Analysis 

Myclobutanil was detected in ambient surface water (Table 3.3) at a detection frequency 

of 37.8 % (166 of 439 samples) collected in five counties in California. The maximum 

daily myclobutanil concentration was 0.507 μg/L for a sampling site located near 

Montpelier California in Merced County California (USGS Sampling Station 

373112120382901). The minimum reporting limit (MRL) varies from 0.0022 to 0.25 

μg/L, with a median MRL of 0.008 μg/L. 

Table 3.3 Distribution of Myclobutanil Concentrations (μg/L) in USGS NAWQA 

Surface Water Monitoring Data Monitoring Data (1998-2007) 

River Basin County No. samples No. Detections Min Max 

Santa Ana Riverside 55 2 0.0118 0.033 

San Joaquin-Tulare Merced 149 89 0.0091 0.507 

San Joaquin 87 25 0.0045 0.021 

Stanislaus 30 15 0.0082 0.380 

Sacramento Sacramento 118 35 0.0094 0.288 

Total 439 166 (37.8%) 0.0045 0.507 

Ground Water Analysis 

Myclobutanil was not detected in ground water in California samples collected in 

California (300 samples). Wells were located in Butte, Colusa, Fresno, Glenn, Madera, 

Merced, Placer, Sacramento, San Bernardino, San Joaquin, Stanislaus, Sutter, Tulare, and 

Yuba Counties. The minimum reporting limit (MRL) varies from 0.0022 to 0.033 μg/L 

with a median MRL of 0.008 μg/L. 

Rain data

Rainfall samples were collected during the growing seasons of 2003 and 2004 at four 

agriculture locations across the United States (Vogel et al., 2008). One of the watersheds 

was located in Western California where the cropland is comprised of almonds and 

vineyards with some corn and dairy. Myclobutanil (Table 3.4) was detected in 74% of 

rain samples (n=23), between February and April corresponding to use after almond trees 

bud. The myclobutanil residues were not detected in the local watershed. 

Table 3.4 Myclobutanil concentrations in Rain in California Agricultural 

Watershed (Vogel et al., 2008) 

Number of samples Percent of 

Detections 

Median Maximum 

23 57 % > 0.01 μg/L 0.014 μg/L 0.113 μg/L 

4 % > 0.1 μg/L 

59
3.2.5 Modeling Results 

The estimated environmental concentrations (EECs) for myclobutanil varied by scenario, 

crop, and by rate and date (i.e., date of first application and reapplication interval), and 

method of application. The dates of the first application of myclobutanil ranged from 

early February to earlier September. The myclobutanil peak concentrations ranged from 

2.11 μg/L to 54.56 μg/L, for cotton seed treatment to the granular application to turf, 

respectively. The 21-day and 60-day rolling averages were 2.1 and 2.08 μg/L, for cotton 

seed treatment and 54.29 to 53.84 μg/L for granular turf, respectively. The selected 

aquatic EECs for myclobutanil for other crops and scenarios and application practice 

(aerial spray, granular, and seed treatment) are listed in Table 3.5. All crops simulated 

(ground and aerial spray) are summarized in Appendix B, Table 1. 

Table 3.5 Aquatic EECs (μg/L) for Myclobutanil Uses in California 

Method Date of First Representative 

Crop 

#@rate/total/Interval EEC 1-year in 10-year 

CA Scenario Application Rate Peak 21day 60 day 

Almond as 2-10 Almond 3@0.2/0.6/7 11.93 11.86 11.77

Citrus as 8-01 Mango 8@0.25/2.0/14 21.75 21.58 21.30

Cotton Seed trt. 4-15 Cotton 0.891 2.11 2.10 2.08

Forestry as 8-05 Douglas fir 2@0.25 + 1@0.1/0.6/14 21.76 21.61 21.46

Forestry as 8-05 Douglas fir 4@0.15/0.6/10 21.74 21.58 21.44

Fruit as 3-10 Apple 4@0.5/2.0/7 29.79 29.45 28.94

Fruit as 3-10 Apple 8@0.25/2.0/7 30.13 29.81 29.49 

Fruit as 4-10 Cherry 2@0/0.47 + 1@0.11/1.31/7 21.25 21.72 20.59

Fruit as 4-10 Cherry 8@0.15 + 1@0.11/1.31/7 21.35 21.09 20.52

Fruit as 4-10 Fruit2 8@0.25/2.0/14 31.35 30.31 30.17 

Fruit as 3-10 Peach 2@0.47 + 1@0.37/1.31/7 19.45 19.24 18.85

Fruit as 3-10 Peach 8@0.15 + 1@0.123/1.31/7 19.88 19.69 19.39

Grapes as 4-01 Grapes 4@0.13 + 1@0.08/0.60/7 8.99 8.88 8.73

Grapes as 4-01 Grapes 6@0.10/0.60/7 9.07 8.98 8.83

Lettuce as 9-02 Lettuce3 4@0.125/0.50/14 41.02 40.58 38.61

Melons as 6-15 Melon 4@0.12 + 1@0.10/0.60/7 16.32 15.74 15.61

Nursery as 7-01 Ornamental 0.26/ns4/2.05/7 45.25 44.93 44.21

Row Crop as 2-15 Artichoke 6@0.10/0.60/7 15.92 15.79 15.55

Row Crop as 7-15 Asparagus 6@0.125/0.76/14 22.29 22.16 21.95

Row Crop as 2-20 Beans 4@0.125/0.50/7 13.62 13.52 13.35

Row Crop as 9-14 Pepper, pimento 4@0.125/0.50/10 17.70 17.52 17.34 

Strawberry as 3-01 Strawberry 6@0.125/0.75/14 34.19 34.03 33.83

Turf Granular 2-01 Turf 6@1.34/ 54.56 54.29 53.84

Turf as 2-01 Turf 4@0.19/0.75/14 20.69 20.53 20.34

60
Representative Method Date of First #@rate/total/Interval EEC 1-year in 10-year Crop 

CA Scenario Application Rate Peak 21day 60 day 

Hops 6 as 9-01 Hops 4@0.25/1.0/7 28.83 28.65 28.38

Hops as 4-01 Hops 4@0.25/1.0/7 17.96 17.82 17.56

1

 Cotton rate is 0.0625 lb a.i./100 lb seed; [4200 seed/lb; 60,000 seed/acre = 14.29 lb seed/acre] 2

 Fruit – Mamey, Mayhaw, Star Apple; canistel 

3 Lettuce and Brussels Sprouts 

4 ns is not specified on label.

5

 Ornamentals – maximum rate = 0.26 lb ai/A/application; season total = 2.0 lb ai/A/year or cc. Number of 

applications is not specified. Maximum seasonal rate is achieved by assuming 7 applications at 0.26 lb ai/A 

and an 8th application at 0.18 to obtain 2.0 lb ai/A per year. Reapplication interval is 7 days. 6 Hops STD Scenario are located in Oregon rather than California 

The estimated environmental concentrations (EECs) for myclobutanil plus 1,2,4-triazole 

varied by scenario, crop, and by rate, date (i.e., date of first application and reapplication 

interval), and method of application. The dates of the first application of myclobutanil 

ranged from early February to earlier September. The myclobutanil peak concentrations 

ranged from 2.84 μg/L to 61.41 μg/L, for cotton seed treatment to the granular 

application to turf, respectively. The 21-day and 60-day rolling averages were 2.82 and 

2.77 μg/L, for cotton seed treatment and 61.15 to 60.71 μg/L for granular turf, 

respectively. The selected aquatic EECs for myclobutanil for other crops and scenarios 

and application practice (aerial spray, granular, and seed treatment) are listed in Table 

3.6. All the crops simulated (ground and aerial spray) are summarized in Appendix B. 

Table 2. 

Table 3.6 EECs California Red legged frog – myclobutanil + 1,2,4-triazole 

Date of First 

Application 

Representative 

Crop 

# @ rate/total 

# @lb ai/A/lb ai/A/days EEC 1-year in 10-year 

CA Scenario Method app Rate peak 21day 60 day 

Almond as 2-10 Almond 3@0.2/0.6/7 14.17 14.10 13.99

Citrus as 8-01 Mango 8@0.25/2.0/14 27.90 27.78 27.37

Forestry as 8-05 Douglas fir 2@0.25 + 1@0.1/0.6/14 22.37 22.28 22.10

Forestry as 8-05 Douglas fir 4@0.15/0.6/10 22.40 22.29 22.11

Fruit as 3-10 Apple 4@0.5/2.0/7 37.75 37.36 36.64

Fruit as 3-10 Apple 8@0.25/2.0/7 37.94 37.63 37.16

Fruit as 4-10 Cherry 2@0/0.47 + 1@0.37/1.31/7 25.87 25.61 25.04

Fruit as 4-10 Cherry 8@0.15 + 1@0.11/1.31/7 24.01 24.51 24.22

Fruit as 4-10 Fruit1 8@0.25/2.0/14 36.33 35.18 35.03

Fruit as 3-10 Peach 2@0.47 + 1@0.37/7 24.55 24.29 23.88

Fruit as 3-10 Peach 8@0.15 + 1@0.123/1.31/7 24.70 24.51 24.22

Grapes as 4-01 Grapes 4@0.13 + 1@0.08/0.60/7 11.18 11.06 10.82

61
Represent- Date of First # @ rate/total ative EEC 1-year in 10-year Application # @lb ai/A/lb ai/A/days Crop 

CA Scenario Method app Rate peak 21day 60 day 

Grapes as 4-01 Grape 6@0.10/0.60/7 11.11 11.02 10.85

Lettuce as 9-02 Lettuce2 4@0.125/0.50/14 41.94 41.79 41.22

Melons as 6-15 Melon 4@0.12 + 1@0.10/0.50/7 18.61 18.41 18.21

Nursery as 7-01 Ornamental 0.26/ns3

/2.04/7 51.96 51.71 51.22

Row Crop as 2-15 Artichoke 6@0.10/0.60/7 17.57 17.46 17.27

Row Crop as 7-15 Asparagus 6@0.125/0.75/14 21.09 20.99 20.68

Row Crop as 2-20 Beans 4@0.125/0.50/7 15.56 15.48 15.35

Row Crop as 9-14 pepper, pimento 4@0.125/0.50/10 16.97 16.91 16.82

Strawberry as 3-01 Strawberry 6@0.125/0.75/14 40.84 40.69 40.41

Strawberry as 3-01 Berries 4@0.063/0.25/10 14.62 14.55 14.43

Turf Granular 2-01 Turf 6@1.34/ 61.41 61.15 60.71

Turf as 2-01 Turf 4@0.19/0.75/14 24.06 23.93 23.78

Hops 5 as 9-01 Hops 4@0.25/1.0/7 28.81 28.65 28.38

Hops as 4-01 Hops 4@0.25/1.0/7 20.52 20.39 20.18 

1

 Fruit – Mamey, Mayhaw, Star Apple; canistel 

2

 Lettuce and Brussels sprouts. 

3

 ns is not specified on label. 4

 Ornamentals – maximum rate = 0.26 lb ai/A/application; season total = 2.0 lb ai/A/year or cc. Number of 

applications is not specified. Maximum seasonal rate is achieved by assuming 7 applications at 0.26 lb ai/A 

and an 8th application at 0.18 to obtain 2.0 lb ai/A per year. Reapplication interval is 7 days. 5

 Hops STD and Mint STD Scenarios are located in Oregon rather than California 

In a previous assessment (USEPA, 2007), it was observed that the Tier II EECs indicated 

year-to-year accumulation of myclobutanil in the standard pond (Figure 3.2). This 

accumulation is not unexpected due to the persistence of myclobutanil and myclobutanil 

plus 1,2,4-triazole in soil and water environments, and the lack of inflow and outflow in 

the standard pond that precludes decreases in concentrations of residues due to dilution. 

62
0

2

4

6

8

10

12

1960 1970 1980 1990

Years

Annual Peak Concentration (ug/L)

Myclobutanil

Myclobutanil + 1,2,4-triazole

Figure 3.2 Accumulation of PRZM/EXAMS Annual Peak Concentrations of 

Myclobutanil and Myclobutanil plus 1,2,4-triazole in the California Tomato 

Scenario (surrogate for CA Okra aerial spray use) 

This apparent accumulation limits any probabilistic interpretation of the return frequency 

of concentrations because of the accumulation over approximately 27 years simulated in 

the standard farm pond. Therefore, the 1-in-10 year concentrations reported in the farm 

pond in the standard EFED ecological risk assessments are conservative compared to 

flowing systems. Modeling of accumulation curves was conducted to allow for estimation 

of concentrations during a 30 year time period. The modeling was conducted on annual 

peak concentrations from PRZM/EXAMS using Sigmaplot Regression Wizard. The 

model used was the exponential rise to maximum model (y = a(1-e(-b*x)) where y = 

annual peak concentration (μg/L), x = time (years), a= plateau concentration of 

accumulation, and b= annual rate of rise (year-1). Table 3.7 shows the model parameters 

for several PRZM/EXAMS simulations. 

63
Table 3.7 Time (years) for myclobutanil and myclobutanil plus 1,2,4-triazole to 

reach plateau concentration in standard farm pond (USEPA, 2007) 

Model Predicted Constants Scenario Application 

Method a

1 b2 R2

Air 6.1507 0.3930 0.87 CA Okra Ground 2.7613 0.4002 0.55 

Air 92.26 0.24 0.76 CA Lettuce Ground 81.23 0.24 0.69 

Air 17.40 0.23 0.94 CA Artichoke Ground 11.45 0.24 0.87 

Air 21.22 0.50 0.72 CA Tropical Fruit Ground 7.66 0.76 0.15 

1

 Years to reach plateau concentration in standard farm pond. 

 2 Annual rate of rise (year-1). 

3.3 Terrestrial Animal Exposure Assessment 

T-REX (Version 1.4.1) is used to calculate dietary and dose-based EECs of myclobutanil 

for the CRLF and its potential prey (e.g. small mammals and terrestrial insects) 

inhabiting terrestrial areas. EECs used to represent the CRLF are also used to represent 

exposure values for frogs serving as potential prey of CRLF adults. T-REX simulates a 1-

year time period. For this assessment, spray and granular applications of myclobutanil 

are considered, as discussed below. In addition, the exposure estimation for use on 

cotton seeds assumes that the seeds are 100% available based on shallow planting 

conditions and an associated planting depth of 1⁄2 inch. 

Terrestrial EECs for foliar formulations of myclobutanil were derived for the uses 

summarized in Table 3.8. Crop-specific decline data for combined residues of 

myclobutanil and the primary metabolite RH-9090 from submitted crop field trial studies 

are available for several commodities. Based on available data, foliar dissipation halflives can be derived for pome fruit and stone fruit (19 days), caneberries (14 days), 

bushberries (25 days) hops (15 days), and peppers (26 days). However, no dissipation 

data are available for the 1,2,4-triazole and triazole conjugates (triazole alanine and 

triazole acetic acid) which are common degradates of myclobutanil. Using conservative 

assumptions that the mode of action of the parent and degradates are similar and that the 

compounds are of equivalent toxicity, a conservative default foliar dissipation half-life of 

35 days based on the work of Willis and McDowell (1987) is used for all uses of 

myclobutanil. Use specific input values, including number of applications, application 

rate and application interval are provided in Table 3.8. An example output from T-REX 

is available in Appendix G. 

64
Table 3.8 Input Parameters for Foliar Applications Used to Derive Terrestrial 

EECs for myclobutanil with T-REX 

Use1 Application rate 

(lbs ai/A) 

Number of 

Applications 

Application 

Interval (days) 

Almond 0.2 3 7 

Apple (pressure spray/hose-end spray) 0.5 4 7 

Apricot (irrigation) 0.5 2 7 

Artichoke 0.125 6 14 

Asparagus 0.125 6 14 

Beans 0.125 4 7 

Blackberry/EggPlant/Okra/Pepper/Raspberry 0.125 4 10 

Boysenberry/Dewberry/Youngberry 0.0625 4 10 

Carrot 0.1875 2 14 

Canistel/Mango/Papaya/Sapodilla 0.25 8 14 

Cherry/Nectarine/Peach (pressure 

spray/chemigation) 0.5 3 

7 

Cotton 0.06 lb ai/cwt NS NS 

Cucurbit Vegetables 0.12 5 7 

Currant 0.125 8 7 

Gooseberry 0.125 8 10 

Grapes 0.1 6 7 

Hops 0.25 4 7 

Lettuce 0.125 4 14 

Plum/Prune 0.16 7 7 

Tomato 0.1 4 21 

Turf (ground) 1.3 4 5 

Turf (granule – broadcast spreader) 1.35 6 14 1

 Aerial Application unless otherwise specified 

T-REX is also used to calculate EECs for terrestrial insects exposed to myclobutanil. 

Dietary-based EECs calculated by T-REX for small and large insects (units of a.i./g) are 

used to bound an estimate of exposure to terrestrial insects. Available acute contact 

toxicity data for bees exposed to myclobutanil (in units of μg a.i./bee), are converted to 

μg a.i./g (of bee) by multiplying by 1 bee/0.128 g. The EECs are later compared to the 

adjusted acute contact toxicity data for bees in order to derive RQs. 

For modeling purposes, exposures of the CRLF to myclobutanil through contaminated 

food are estimated using the EECs for the small bird (20 g) which consumes small 

insects. Dietary-based and dose-based exposures of potential prey are assessed using the 

small mammal (15 g) which consumes short grass. Upper-bound Kenega nomogram 

values reported by T-REX for these two organism types are used for derivation of EECs 

for the CRLF and its potential prey (Table 3.9). Dietary-based EECs for small and large 

insects reported by T-REX as well as the resulting adjusted EECs are available in Table 

3.10. An example output from T-REX v. 1.3.1 is available in Appendix G. 

65
Table 3.9 Upper-bound Kenega Nomogram EECs for Dietary- and Dose-based 

Exposures of the CRLF and its Prey to Myclobutanil 

EECs for CRLF EECs for Prey 

(small mammals) 

Use Dietarybased EEC 

(ppm) 

Dose-based 

EEC 

(mg/kg-bw) 

Dietarybased 

EEC 

(ppm) 

Dose-based 

EEC 

(mg/kg-bw) 

Almond 71 81 126 120 

Apple 222 253 395 376 

Apricot 126 143 225 214 

Artichoke 45 51 80 77 

Asparagus 56 64 100 96 

Beans 55 63 99 94 

Blackberry/EggPlant/Okra/Pepper/Raspberry 52 59 91 87 

Boysenberry/Dewberry/Youngberry 26 29 46 44 

Carrot 45 51 79 75 

Canistel/Mango/Papaya/Sapodilla 124 141 221 211 

Cherry/Nectarine/Peach 177 202 315 301 

Cucurbit Vegetables 63 71 111 106 

Currant 59 67 104 99 

Gooseberry 75 85 133 127 

Grapes 77 87 136 100 

Hops 111 126 197 188 

Lettuce 47 53 83 79 

Plum/Prune 103 118 175 184 

Tomato 37 32 57 55 

Turf 609 693 1082 1031 

66
Table 3.10 EECs (ppm) for Indirect Effects to the Terrestrial-Phase CRLF via 

Effects to Terrestrial Invertebrate Prey Items 

Use Small Insect Large Insect 

Almond 71 8 

Apple 221 25 

Apricot 126 14 

Artichoke 45 5 

Asparagus 56 6 

Beans 55 6 

Blackberry/EggPlant/Okra/Pepper/Raspberry 51 6 

Boysenberry/Dewberry/Youngberry 26 3 

Carrot 45 5 

Canistel/Mango/Papaya/Sapodilla 124 14 

Cherry/Nectarine/Peach 177 20 

Cotton NA NA 

Cucurbit Vegetables 63 7 

Currant 59 7 

Gooseberry 75 8 

Grapes 77 9 

Hops 111 12 

Lettuce 47 5 

Plum/Prune 104 12 

Tomato 32 4 

Turf 609 68 

Turf (granular) 504 56 

Myclobutanil is applied as a 0.62% ai granular formulation to non-residential and 

residential turf grass at a rate of 1.35 lb ai per acre. Therefore a quantitative analysis of 

terrestrial exposure to granular formulations was conducted. For granular applications, 

an LD50 per square foot is estimated based on application rate and toxicity. 

3.4 Terrestrial Plant Exposure Assessment 

TerrPlant (Version 1.1.2) is used to calculate EECs for non-target plant species inhabiting 

dry and semi-aquatic areas. Due to the lack of terrestrial plant data with myclobutanil, 

toxicity data on other conazole fungicides were used with TerrPlant and discussed in the 

risk description (Section 5.2.3.2). Parameter values for application rate, drift assumption 

and incorporation depth are based upon the use and related application method (Tables 

2.2 and 3.5). As classified by Terrplant, a runoff value of 0.05 (5%) is utilized based on 

the solubility of myclobutanil (142 ppm). For aerial and ground application methods, 

drift is assumed to be 5% and 1%, respectively. EECs relevant to terrestrial plants 

consider pesticide concentrations in drift and in runoff. These EECs are listed by use in 

Table 3.11. An example output from TerrPlant v.1.2.2 is available in Appendix N. 

67
Table 3.11 TerrPlant Inputs and Resulting EECs for Plants Inhabiting Dry and 

Semi-aquatic Areas Exposed to Myclobutanil via Runoff and Drift 

Use 

Application 

rate 

(lbs a.i./A) 

Application 

method 

Drift 

Value 

(%) 

Spray 

drift 

EEC 

(lbs 

a.i./A) 

Dry 

area 

EEC 

(lbs 

a.i./A) 

Semiaquatic 

area 

EEC 

(lbs 

a.i./A) 

Boysenberry/Dewberry/Youngberry 0.0625 Foliar – aerial 0.05 0.003 0.006 0.034 

Boysenberry/Dewberry/Youngberry 0.0625 Foliar - ground 0.01 0.0006 0.004 0.032 

Grapes, tomato 0.1 Foliar – aerial 0.05 0.005 0.010 0.055 

Grapes, tomato 0.1 Foliar - ground 0.01 0.001 0.006 0.051 

Cucurbit Vegetables 0.12 Foliar – aerial 0.05 0.006 0.012 0.066 

Cucurbit Vegetables 0.12 Foliar - ground 0.01 0.001 0.007 0.061 

Artichoke, Asparagus, Beans, 

Blackberry/EggPlant/Okra/Pepper/ 

Raspberry, Currant, Gooseberry, 

Lettuce 0.125 

Foliar – aerial 0.05 0.006 0.013 0.069 

Artichoke, Asparagus, Beans, 

Blackberry/EggPlant/Okra/Pepper/ 

Raspberry, Currant, Gooseberry, 

Lettuce 0.125 

Foliar - ground 0.01 0.001 0.008 0.064 

Plum/Prune 0.16 Foliar – aerial 0.05 0.008 0.016 0.088 

Plum/Prune 0.16 Foliar - ground 0.01 0.002 0.010 0.082 

Carrot, Hops 0.1875 Foliar – aerial 0.05 0.009 0.019 0.103 

Carrot, Hops 0.1875 Foliar - ground 0.01 0.002 0.011 0.096 

Almond 0.2 Foliar - aerial 0.05 0.010 0.020 0.110 

Almond 0.2 Foliar - ground 0.01 0.002 0.012 0.102 

Canistel/Mango/Papaya/Sapodilla 0.25 Foliar – aerial 0.05 0.013 0.025 0.138 

Canistel/Mango/Papaya/Sapodilla 0.25 Foliar - ground 0.01 0.003 0.015 0.128 

Apple, Apricot, 

Cherry/Nectarine/Peach 0.5 Foliar - aerial 0.05 0.025 0.050 0.175 

Apple, Apricot, 

Cherry/Nectarine/Peach 0.5 Foliar - ground 0.01 0.005 0.030 0.255 

Turf 1.3 Foliar - ground 0.01 0.013 0.078 0.663 

Turf 1.35 

Granule 

broadcast spreader 0.00 0.00 0.068 0.675 

4 Effects Assessment 

This assessment evaluates the potential for myclobutanil to directly or indirectly affect 

the CRLF or affect its designated critical habitat. As discussed in Section 2.8, assessment 

endpoints for the CRLF effects determination include direct toxic effects on the survival, 

reproduction, and growth of CRLF, as well as indirect effects, such as reduction of the 

prey base or effects to its habitat. In addition, potential effects to critical habitat are 

assessed by evaluating effects to the PCEs, which are components of the critical habitat 

areas that provide essential life cycle needs of the CRLF. Direct effects to the aquaticphase of the CRLF are based on toxicity information for freshwater fish, while terrestrialphase effects are based on avian toxicity data, given that birds are generally used as a 

68
surrogate for terrestrial-phase amphibians. Because the frog’s prey items and habitat 

requirements are dependent on the availability of freshwater fish and invertebrates, small 

mammals, terrestrial invertebrates, and aquatic and terrestrial plants, toxicity information 

for these taxa are also discussed. Acute (short-term) and chronic (long-term) toxicity 

information is characterized based on registrant-submitted studies and a comprehensive 

review of the open literature on myclobutanil. 

As described in the Agency’s Overview Document (U.S. EPA, 2004), the most sensitive 

endpoint for each taxon is used for risk estimation. For this assessment, evaluated taxa 

include freshwater fish (surrogate for aquatic-phase amphibians), freshwater 

invertebrates, aquatic plants, birds (surrogate for terrestrial-phase amphibians), mammals, 

and terrestrial invertebrates. No acceptable data were available for aquatic or terrestrial 

phase amphibians and terrestrial plants. 

Toxicity endpoints are established based on data generated from guideline studies 

submitted by the registrant, and from open literature studies that meet the criteria for 

inclusion into the ECOTOX database maintained by EPA/Office of Research and 

Development (ORD) (U.S. EPA, 2004). Open literature data presented in this assessment 

were obtained from ECOTOX information obtained on October 31, 2008. In order to be 

included in the ECOTOX database, papers must meet the following minimum criteria: 

(1) the toxic effects are related to single chemical exposure; 

(2) the toxic effects are on an aquatic or terrestrial plant or animal species; 

(3) there is a biological effect on live, whole organisms; 

(4) a concurrent environmental chemical concentration/dose or application 

rate is reported; and 

(5) there is an explicit duration of exposure. 

Data that pass the ECOTOX screen are evaluated along with the registrant-submitted 

data, and may be incorporated qualitatively or quantitatively into this endangered species 

assessment. In general, effects data in the open literature that are more conservative than 

the registrant-submitted data are considered. The degree to which open literature data are 

quantitatively or qualitatively characterized for the effects determination is dependent on 

whether the information is relevant to the assessment endpoints (i.e., maintenance of 

CRLF survival, reproduction, and growth) identified in Section 2.8. For example, 

endpoints such as behavior modifications are likely to be qualitatively evaluated, because 

quantitative relationships between modifications and reduction in species survival, 

reproduction, and/or growth are not available. Although the effects determination relies 

on endpoints that are relevant to the assessment endpoints of survival, growth, or 

reproduction, it is important to note that the full suite of sublethal endpoints potentially 

available in the effects literature (regardless of their significance to the assessment 

endpoints) are considered to define the action area for myclobutanil. 

Citations of all open literature not considered as part of this assessment because they 

were either rejected by the ECOTOX screen or accepted by ECOTOX but not used (e.g., 

the endpoint is less sensitive) are included in Appendix H. Appendix H also includes a 

69
rationale for rejection of those studies that did not pass the ECOTOX screen and those 

that were not evaluated as part of this endangered species risk assessment. A detailed 

spreadsheet of the available ECOTOX open literature data, including the full suite of 

lethal and sublethal endpoints is presented in Appendix I. Appendix J contains a 

summary of the human health effects data for myclobutanil. 

In addition to registrant-submitted and open literature toxicity information, other sources 

of information, including use of the acute probit dose response relationship to establish 

the probability of an individual effect and reviews of the Ecological Incident Information 

System (EIIS), are conducted to further refine the characterization of potential ecological 

effects associated with exposure to myclobutanil. A summary of the available aquatic 

and terrestrial ecotoxicity information, use of the probit dose response relationship, and 

the incident information for myclobutanil are provided in Sections 4.1 through 4.4, 

respectively. 

There are three registrant-submitted studies on the toxicity of the 1,2,4-triazole degradate 

to aquatic organisms, but they are pending review. From these studies, it is provisionally 

concluded that 1,2,4-triazole has no greater toxicity to aquatic organisms than the parent 

compound, myclobutanil. There are currently no open literature studies reported in the 

ECOTOX database for 1,2,4-triazole. Each of the registrant submitted studies is briefly 

summarized below. 

A rainbow trout (Salma gairdneri) acute toxicity study (MRID 45284017) was 

submitted for 1,2,4-triazole. Mortality was observed only in the highest test level 

(1000 mg/L). The calculated LC50 was 760 mg/L. For myclobutanil, the rainbow 

trout showed a 96-hour LC50 of 4.2 (3.2 to 5.6, 95% C.I.) mg a.i./L (MRID 

00141677). The most sensitive endpoint for myclobutanil was the bluegill sunfish 

96-hour LC50 of 2.4 (1.5 to 4.7, 95% C.I.) mg a.i/L (MRID 00144285). 

Therefore, 1,2,4-triazole shows significantly less toxicity than myclobutanil. 

A water flea (Daphnia magna) acute toxicity study was submitted for 1,2,4-

triazole (MRID 00133381). The calculated LC50 was 900 (730 to 2200, 95% C.I.) 

mg/L. The myclobutanil Daphnia magna 48-hour LC50 was 11 (9.5 to 13, 95% 

C.I.) mg a.i./L (MRID 00141678). Therefore, 1,2,4-triazole shows significantly 

less toxicity than myclobutanil. 

A non-vascular aquatic plant study for a green algae (Scenedesmus subspicatus) 

was submitted for 1,2,4-triazole (MRID 00133382). The calculated EC50 was 6.3 

(5.5 to 7.1, 95% C.I.) mg/L. For myclobutanil, the freshwater green algae 

Selenastrum capricornutum showed a 120-hour EC50 of 0.83 (0.56 to 1.1, 95% 

C.I.) mg a.i./L based on cell density (MRID 419848-01). It is not certain which of 

these species is more or less sensitive, therefore it is provisionally concluded that 

1,2,4-triazole shows less toxicity than myclobutanil. 

Available acute and reproduction studies on the degradate 1,2,4-triazole indicate that for 

mammals, the degradate is either less or equally toxic as the parent. For birds, a report 

70
was submitted which indicates that 1,2,4-triazole does not have a determinate acute 

toxicity value with coturnix quail under the conditions of the study but is possibly less 

toxic than the parent, myclobutanil. This report also indicated that a single oral dose of 

the triazole degradate to male birds does not indicate any reproductive effects; however, 

the protocol of this study is not comparable to the typical avian reproduction study. 

Acute mammalian toxicity data on myclobutanil formulations, including those mixed 

with other pesticides indicate that with one exception (the 60% formulation) the 

formulations are not more acutely toxic than the technical grade compound. The rat LD50

for the technical product is 1600 mg/kg bw, the rat LD50 for the 60% formulation is 980 

mg/kg bw. Therefore, EEC’s were derived separately for the 60% formulation using the 

rat LD50 and actual use parameters (i.e., label specified use and application rate) to 

determine the toxicity of the formulation relative to the technical product and/or other 

formulations in the field. A detailed summary of the available ecotoxicity information 

for 1,2,4-triazole and all myclobutanil formulated products is presented in Appendix K. 

The submitted study citations can be found in Appendix O. 

4.1 Evaluation of Aquatic Ecotoxicity Studies 

Table 4.1 summarizes the most sensitive aquatic toxicity endpoints for the CRLF, based 

on an evaluation of both the submitted studies and the open literature, as previously 

discussed. A brief summary of submitted and open literature data considered relevant to 

this ecological risk assessment for the CRLF is presented below. 

Table 4.1 Freshwater Aquatic Toxicity Profile for Myclobutanil 

Assessment Endpoint Species Toxicity Value Used in 

Risk Assessment 

MRID Study 

Classification 

Acute Direct Toxicity to 

Aquatic-Phase CRLF Bluegill sunfish 

(Lepomis 

macrochirus) 

LC50 = 2.4 mg/L 00144285 Acceptable 

Chronic Direct Toxicity 

to Aquatic-Phase CRLF 

Fathead minnow 

(Pimephales 

promelas)

NOAEC = 0.98 mg/L 

LOAEC = 2.2 mg/L 

00164986 

40409201 

40480401 

Acceptable 

Indirect Toxicity to 

Aquatic-Phase CRLF via 

Acute Toxicity to 

Freshwater Invertebrates 

(i.e. prey items) 

Water flea 

(Daphnia 

magna)

LC50 = 11 mg/L 00141678 Acceptable 

Indirect Toxicity to 

Aquatic-Phase CRLF via 

Chronic Toxicity to 

Freshwater Invertebrates 

(i.e. prey items) 

No data available for myclobutanil 

71
Assessment Endpoint Species Toxicity Value Used in 

Risk Assessment 

MRID Study 

Classification 

Indirect Toxicity to 

Aquatic-Phase CRLF via 

Toxicity to Non-vascular 

Aquatic Plants 

Freshwater green 

algae 

(Selenastrum 

capricornutum) 

EC50 = 0.83 mg/L 419848-01 Acceptable 

Tier II growth 

and 

reproduction 

Indirect Toxicity to 

Aquatic-Phase CRLF via 

Toxicity to Vascular 

Aquatic Plants 

No data available for myclobutanil 

Toxicity to aquatic fish and invertebrates is categorized using the system shown in Table 

4.2 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined. 

Table 4.2 Categories of Acute Toxicity for Fish and Aquatic Invertebrates 

LC50 (ppm) Toxicity Category 

< 0.1 Very highly toxic 

> 0.1 - 1 Highly toxic 

> 1 - 10 Moderately toxic 

> 10 - 100 Slightly toxic 

> 100 Practically nontoxic 

4.1.1 Toxicity to Freshwater Fish 

Given that no acceptable myclobutanil toxicity data are available for aquatic-phase 

amphibians, freshwater fish data were used as a surrogate to estimate direct acute and 

chronic risks to the CRLF. Freshwater fish toxicity data were also used to assess 

potential indirect effects of myclobutanil to the CRLF. Effects to freshwater fish 

resulting from exposure to myclobutanil may indirectly affect the CRLF via reduction in 

available food. As discussed in Section 2.5.3, over 50% of the prey mass of the CRLF 

may consist of vertebrates such as mice, frogs, and fish (Hayes and Tennant, 1985). 

A summary of acute and chronic freshwater fish data is provided below in Sections 

4.1.1.1 through 4.1.1.3. 

4.1.1.1 Freshwater Fish: Acute Exposure (Mortality) Studies 

Available data indicate that myclobutanil is moderately toxic on an acute basis to two 

surrogate freshwater fish species (Appendix K). The most sensitive endpoint, the bluegill 

sunfish 96-hour LC50 of 2.4 (1.5-4.7, 95% C.I.) mg a.i./L (MRID 00144285) will be used 

to calculate RQs for direct effects to the aquatic-phase CRLF. The probit dose-response 

slope used for this study is the default of 4.5 (2-9) because there were less than two 

concentrations at which the percent dead was between 0 and 100, thus a statistically 

sound calculation of the slope cannot be made from the experimental data. The acute 

72
study available for rainbow trout reported a 96-hour LC50 of 4.2 (3.2-5.6, 95% C.I.) mg 

a.i./L (MRID 00141677). 

4.1.1.2 Freshwater Fish: Chronic Exposure (Early Life Stage and 

Reproduction) Studies 

There is one submitted early life stage study for chronic freshwater fish toxicity to 

myclobutanil (MRID 00164986, 40409201, 40480401). Total length of juvenile fish at 

the end of the 35-day exposure was the most sensitive endpoint for the fathead minnow 

(Pimephales promelas); the reported NOAEC and LOAEC were 0.98 mg/L and 2.2 

mg/L, respectively. At the LOAEC (2.2 mg/L) there was a 9.7% reduction in mean total 

length compared to the control. The LOAEC for growth as determined by wet weight 

was reported as 4 mg/L. The 8-day egg survival showed no significant differences 

between the control and any of the tested concentrations. After 35 days of exposure, 

100% mortality occurred at 8.5 mg/L, the highest concentration tested. 

4.1.1.3 Freshwater Fish: Sublethal Effects and Additional Open 

Literature Information 

In the bluegill sunfish acute toxicity study (MRID 00144285) used to calculate RQs, it 

was reported that the test organisms exhibited quiescence and loss of equilibrium prior to 

death at 2.7 mg/L (LOAEC). The NOAEC for this study was 1.5 mg/L. The rainbow 

trout acute toxicity study (MRID 00141677) reported toxic symptoms at 3.2 mg/L 

(LOAEC) - the fish exhibited loss of equilibrium, surfacing, and dark coloration. 

Mortality was observed at 5.6 mg/L and above. The NOAEC was 1.8 mg/L 

In the chronic fish early life stage study for myclobutanil (MRID 00164986, 40409201, 

40480401), the raw data indicates no differences in behavior on any groups analyzed. 

Total length was the most sensitive endpoint. The reported NOAEC and LOAEC for 

total length were 0.98 mg/L and 2.2 mg/L, respectively. 

There were no studies on myclobutanil toxicity to freshwater fish identified in the open 

literature. 

4.1.1.4 Aquatic-phase Amphibian: Acute and Chronic Studies 

There were no acceptable studies available for myclobutanil on toxicity to aquatic-phase 

amphibians. 

4.1.2 Toxicity to Freshwater Invertebrates 

Freshwater invertebrate toxicity data were used to assess potential indirect effects of 

myclobutanil to the CRLF. Effects to freshwater invertebrates resulting from exposure to 

73
myclobutanil could indirectly affect the CRLF via reduction in available food items. As 

discussed in Section 2.5.3, the main food source for juvenile aquatic- and terrestrialphase CRLFs is thought to be aquatic invertebrates found along the shoreline and on the 

water surface, including aquatic sowbugs, larval alderflies and water striders. 

A summary of acute and chronic freshwater invertebrate data is provided below in 

Sections 4.1.2.1 through 4.1.2.3. 

4.1.2.1 Freshwater Invertebrates: Acute Exposure (Mortality) Studies 

Available data indicate that myclobutanil is slightly toxic on an acute basis to Daphnia 

magna. The available study (MRID 00141678) reported the 48-hour LC50 for 

myclobutanil was 11 (9.5-13, 95% C.I.) mg a.i./L. The probit dose-response slope for 

this study is 6.8 (4.1-9.6, 95% C.I.). 

4.1.2.2 Freshwater Invertebrates: Chronic Exposure (Reproduction) 

Studies 

There are currently no submitted chronic freshwater invertebrate studies available for 

myclobutanil. It was not possible to estimate a chronic toxicity value for freshwater 

invertebrates using an acute to chronic ratio with estuarine/marine invertebrate data 

because no chronic studies are available for myclobutanil. In lieu of any myclobutanil 

data, toxicity data from other conazole (DMI triazole) fungicides were used to 

characterize risk to freshwater invertebrates, assuming that myclobutanil toxicity is 

similar to other conazoles due to similar mode of action. Toxicity data were obtained 

from the EFED database (registrant-submitted studies) for the chemicals categorized as 

conazole fungicides (DMI triazoles) by the Fungicide Resistance Action Committee 

(FRAC)3

. Acute to chronic ratios were calculated only for conazoles with acute and 

chronic water flea (Daphnia magna) studies (the species for which acute data are 

available for myclobutanil). Furthermore, the only studies considered were those 

categorized as acceptable or supplemental, tested the technical product, and resulted in a 

definitive endpoint. Table 4.3 summarizes the toxicity endpoints for the nine conazole 

fungicides that met these data standards. 

In addition to studies on the water flea (Daphnia magna), four of the conazoles had 

studies submitted for other aquatic invertebrate taxa (Fenbuconazole: MRID 46553601, 

Prothioconazole: MRID 46246131, Tetraconazole: MRID 46614304, and Triadimefon: 

MRID 00149324). For these four conazoles, Daphnia magna is the most sensitive 

aquatic invertebrate species tested. 

 

3 http://www.frac.info/frac/index.htm

74
Table 4.3 Conazole (DMI triazole) Fungicide Chronic Toxicity to Aquatic 

Invertebrates 

Conazole1 48-hr 

EC50/LC50

(mg/L) 

MRID/ 

Study 

Classification

NOAEC 

(mg/L) 

Most sensitive 

parameter 

MRID/ 

Study 

Classification 

ACR2

26 40607735/ 

Acceptable 

0.019 Reproduction (# live 

offspring) 

47036201/ 

Supplemental 

1368a Cyproconazole 

0.29 Reproduction (# live 

offspring) 

43187701/ 

Acceptable 

89.6a

Difenoconazole 0.77 42245110/ 

Acceptable 

0.0056 Number of young per 

adult per reproductive 

day and adult length 

42245114/ 

Supplemental 

137.5 

Fenbuconazole 2.3 41073507/ 

Acceptable 

0.078 Reproduction and 

length 

41875007/ 

Supplemental 

29.5 

Hexaconazole 2.9 00160502/ 

Acceptable 

0.226 Total young and young 

per female reproductive 

day and length 

42147301/ 

Acceptable 

12.8 

Prothioconazole 1.2 46246009/ 

Acceptable 

0.51 Number of offspring 

per parent per 

reproduction day and 

terminal length 

46246028/ 

Acceptable 

2.4 

Tebuconazole 4 40700913/ 

Acceptable 

0.120 Adult length and 

survival and young per 

adult per reproduction 

day 

40700915/ 

Acceptable 

33.3 

3.07 45823201/ 

Acceptable 

0.19 Time to first brood 

release and 

reproduction 

(neonates/adult) 

45823207/ 

Acceptable 

13.8b

 to 

16.2c

Tetraconazole 

2.63 44367018/ 

Supplemental 

0.51 Survival and 

reproduction 

44367019/ 

Supplemental 

5.2b

 to 6.0c

7.16 43257001/ 

Acceptable 

0.052 Adult length 41922102/ 

Supplemental 

137.7d Triadimefon 

0.087 Reproduction 00094679/ 

Supplemental 

82.3d

Triadimenol 2.5 00126282/ 

Acceptable 

0.199 Reproduction (# young 

produced) 

00094680/ 

Acceptable 

12.6 

1

 Based on toxicity to Daphnia magna 2

 Acute-to chronic ratio 

a

 Based on acute toxicity of 26 mg/L 

b

 Based on acute toxicity of 2.63 mg/L 

c

 Based on acute toxicity of 3.07 mg/L 

d

 Based on acute toxicity of 7.16 mg/L 

75
4.1.2.3 Freshwater Invertebrates: Sublethal Effects and Open 

Literature Data 

In the Daphnia magna acute toxicity study (MRID 00141678) used to calculate RQs, it 

was reported that the test organisms settled to the bottom of the test vessel at 5.6 mg/L 

(LOAEC) and above. The NOAEC for this study was 3.2 mg/L. 

There were no studies on toxicity to freshwater invertebrates identified in the open 

literature. 

4.1.3 Toxicity to Aquatic Plants 

Aquatic plant toxicity studies were used as one of the measures of effect to evaluate 

whether myclobutanil may affect primary production and the availability of aquatic 

plants as food for CRLF tadpoles. Primary productivity is essential for indirectly 

supporting the growth and abundance of the CRLF. 

Laboratory studies were considered for determining whether myclobutanil may cause 

direct effects to aquatic plants. A summary of the laboratory data and freshwater field 

studies for aquatic plants is provided in Sections 4.1.3.1 and 4.1.3.2. There were no 

studies on toxicity to aquatic plants identified in the open literature. 

4.1.3.1 Aquatic Plants: Laboratory Data 

The available study for non-vascular aquatic plants (MRID 419848-01) examined the 

freshwater green algae Selenastrum capricornutum. This study reported a 120-hour EC50 

for myclobutanil of 0.83 (0.56-1.1, 95% C.I.) mg a.i./L based on cell density. The 

NOAEC for this study was 0.56 mg/L (mean measured concentration). 

There are currently no submitted studies for vascular aquatic plants available for 

myclobutanil. In lieu of any myclobutanil data, toxicity data from other conazole (DMI 

triazole) fungicides were used to characterize risk to aquatic vascular plants, assuming 

that myclobutanil toxicity is similar to other conazoles due to similar mode of action. 

Conazole toxicity data were obtained from the EFED database as described in section 

4.1.2.2. Table 4.4 summarizes the toxicity endpoints for the seven conazoles with studies 

categorized as acceptable or supplemental that tested the technical product and resulted in 

a definitive endpoint. 

Table 4.4 Conazole (DMI Triazole) Fungicide Toxicity to Aquatic Vascular Plants 

Conazole EC50 (mg/L) 1 Most sensitive 

parameter MRID Study Classification 

Bromuconazole 0.16 Frond production 42937141 Acceptable 

Difenoconazole 1.9 Frond number 46950204 Supplemental 

Metconazole 0.022 Frond number 46808428 Acceptable 

76
Conazole Most sensitive EC50 (mg/L) 1 MRID Study Classification parameter 

Propiconazole 9.02 Frond production 00133363 Supplemental 

Prothioconazole 0.073 Frond number 46246101 Acceptable 

Tetraconazole 0.31 Frond number 45842201 Acceptable 

Triticonazole 1.4 Frond number 44802119 Acceptable 1

 Based on toxicity to duckweed (Lemna gibba) 

4.1.3.2 Freshwater Field Studies 

There are currently no submitted freshwater aquatic plant field studies available for 

myclobutanil. 

4.2 Toxicity of Myclobutanil to Terrestrial Organisms 

Table 4.5 summarizes the most sensitive terrestrial toxicity endpoints for the CRLF, 

based on an evaluation of both the submitted studies and the open literature. In addition 

to the parent myclobutanil, toxicity data on metabolites and degradates are also 

considered when available. RH-9090 [α-(3-hydroxybutyl)-α-(4-chlorophenyl)-1H-1,2,4-

triazole-1-propanenitrile] 6-chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] 

(free and bound) is a major metabolite of myclobutanil in plants i.e., > 10%. RH-9090 is 

considered to be of equivalent toxicity to the parent based on structural activity 

relationship (SAR). In addition, 1,2,4-triazole and triazole conjugates (triazole alanine 

and triazole acetic acid) are common degradates of triazole compounds, including 

myclobutanil. A brief summary of submitted and open literature data considered relevant 

to this ecological risk assessment for the CRLF is presented below. 

Table 4.5 Terrestrial Toxicity Profile for Myclobutanil 

Assessment Endpoint Species Toxicity Value Used in 

Risk Assessment 1 

Citation/ 

MRID # 

Study 

Classification 

Acute Dose-based Direct 

Toxicity to TerrestrialPhase CRLF 

Bobwhite Quail 

(Colinus 

virginianus) 

LD50 = 498 mg/kg bw 00144286 Acceptable 

Acute Dietary-based Direct 

Toxicity to TerrestrialPhase CRLF 

Mallard Duck 

(Anas 

platyrhynchos) 

LC50 = >4090 ppm 00144288 Acceptable 

Chronic Direct Toxicity to 

Terrestrial-Phase CRLF 

Bobwhite Quail 

(Colinus 

virginianus) 

NOAEC = 256 ppm 

LOAEC >256 ppm: 

43087901 Supplemental 

Indirect Toxicity to 

Terrestrial-Phase CRLF 

(via acute toxicity to 

mammalian prey items) 

Mouse LD50 =1360 mg/kg 00165239 

00141662 

Acceptable 

Indirect Toxicity to 

Terrestrial-Phase CRLF 

Rat NOAEC = 200 ppm 

LOAEC = 1000 ppm 

00149581 

00143766 

Acceptable 

77
Assessment Endpoint Species Toxicity Value Used in 

Risk Assessment 1 

Citation/ Study 

MRID # Classification 

(via chronic toxicity to 

mammalian prey items) 

NOAEL = 16 mg/kg 

bw/day 

LOAEL = 80 mg/kg 

bw/day 

Indirect Toxicity to 

Terrestrial-Phase CRLF 

(via acute toxicity to 

terrestrial invertebrate prey 

items) 

Honey bee LD50 = > 100 μg a.i. 

bee (dust) 

00144289 Acceptable 

Seedling 

Emergence 

Monocots 

Seedling 

Emergence 

Dicots 

Vegetative Vigor 

Monocots 

Indirect Toxicity to 

Terrestrial- and AquaticPhase CRLF (via toxicity 

to terrestrial plants) 

Vegetative Vigor 

Dicots 

No Data Available 

1

 All studies were conducted with the technical material (approximately 96% pure) and the toxicity values are 

adjusted for %a.i. 

Acute toxicity to terrestrial animals is categorized using the classification system shown 

in Table 4.6 (U.S. EPA 2004). Toxicity categories for terrestrial plants have not been 

defined. 

Table 4.6 Categories of Acute Toxicity for Avian and Mammalian Studies 

Toxicity Category Oral LD50 Dietary LC50

Very highly toxic < 10 mg/kg < 50 ppm 

Highly toxic 10 - 50 mg/kg 50 - 500 ppm 

Moderately toxic 51 - 500 mg/kg 501 - 1000 ppm 

Slightly toxic 501 - 2000 mg/kg 1001 - 5000 ppm 

Practically non-toxic > 2000 mg/kg > 5000 ppm 

4.2.1 Toxicity to Birds 

As specified in the Overview Document, the Agency uses birds as a surrogate for 

terrestrial-phase amphibians when amphibian toxicity data are not available (U.S. EPA, 

2004). No terrestrial-phase amphibian data are available for myclobutanil; therefore, 

acute and chronic avian toxicity data are used to assess the potential direct effects of 

myclobutanil to terrestrial-phase CRLFs. 

4.2.1.1 Birds: Acute Exposure (Mortality) Studies 

Based on the submitted acute oral toxicity study for the Bobwhite Quail (MRID 

00144286), myclobutanil is categorized as moderately toxic to birds on a dose basis with 

an acute LD50 of 498 (408-598, 95% C.I.) mg/kg bw. 

78
Based on avian subacute dietary studies for two bird species, myclobutanil is categorized 

as slightly toxic on a dietary basis with subacute dietary LC50’s of >4090 ppm for mallard 

duck (MRID 00144288) and > 4530 ppm for bobwhite quail (MRID 00144287). 

Although no definitive subacute dietary LC50s could be determined from these studies, 

there were mortalities in both studies. There was one mortality at 4090 ppm, the highest 

concentration tested in the mallard duck study and mortalities at 3000 ppm and 4530 

ppm, the highest concentration tested in the bobwhite quail study. 

Table 4.7 Avian Acute Toxicity Data 

Common 

Name

%AI Study parameters LD50/LC50 NOAEC/ 

LOAEC

MRID Classification/

Category

Bobwhite 

Quail 

Colinus 

virginianus

84.5 Acute oral study 

10 birds/dose level 

21 day observation 

period 

0 (vehicle), 316, 

464, 681, 1000, 

1470 mg/kg tested 

LD50 498 (408 – 598) 

mg/kg bw1

Slope = 7.03 (3.5-10.5) 

NOAEL not 

determined 

LOAEL 316 mg/kg 

(lethargy and anorexia). 

Mortalities at all dose 

levels (1, 4, 8, 10 and 

10, respectively). 

Good dose response; 

NOAEL not critical in 

this case. 

00144286 Acceptable 

Moderately 

toxic

Bobwhite 

Quail 

Colinus 

virginianus

84.5 Subacute dietary 

study 

10 

birds/concentration 

level 

5 days on 

treatment, 3 days 

observation 

0 (vehicle), 246, 

641, 1150, 3000, 

4530 ppm tested 

(measured 

concentrations) 

LC50 >4530 ppm 

NOAEC: 1150 ppm 

LOAEC: 3000 ppm 

Mortality: 2 at 3000 

ppm and 1 at 4530 

ppm. 

Anorexia and lethargy 

at 3000 and 4530 ppm 

00144287 Acceptable 

Slightly toxic

79
Common %AI Study parameters LD50/LC50 NOAEC/ MRID Classification/

Name LOAEC Category

Mallard 

Duck 

Anas 

platyrhync

hos

84.5 Subacute dietary 

study 

10 

birds/concentration 

level 

5 days on 

treatment, 3 days 

observation 

0 (vehicle), 270, 

620, 1250, 2220, 

4090 ppm tested 

(measured 

concentrations) 

LC50 >4090 ppm

NOAEC: 1250 ppm 

LOAEC: 2220 ppm 

(anorexia and lethargy). 

One bird died at 4090 

ppm. 

00144288 Acceptable 

Slightly toxic 

1 Bold value is the value that will be used to calculate risk quotients 

4.2.1.2 Birds: Chronic Exposure (Growth, Reproduction) Studies 

Two avian chronic toxicity studies are available for myclobutanil. One-generation 

reproductive toxicity studies were conducted on both the mallard duck and bobwhite 

quail (MRID numbers 43087901 and 43087902). The studies were conducted 

simultaneously using the same dosing regimen. In both studies, no adverse effects were 

seen at the maximum level tested. Therefore, the NOAEC for both studies is 256 ppm 

and the LOAEC is > 256 ppm. The studies are classified as supplemental since no 

LOAEC was established and the concentrations tested are expected to be relatively low 

when compared to terrestrial EECs . The NOAEC of 256 ppm is used for risk estimation. 

RH-9090 [α-(3-hydroxybutyl)-α-(4-chlorophenyl)-1H-1,2,4-triazole-1-propanenitrile] 6-

chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine] (free and bound) is a major 

metabolite of myclobutanil in plants i.e., > 10%. RH-9090 is considered to be of 

equivalent toxicity to the parent based on structural activity relationship (SAR). In 

addition, 1,2,4-triazole and triazole conjugates (triazole alanine and triazole acetic acid) 

are common degradates of triazole compounds, including myclobutanil. A submitted 

report is available which indicates that the acute LD50 of the 1,2,4-triazole degradate in 

coturnix quail is >316 mg triazole/kg bird (MRID 45284015). This report also contains a 

reproduction study in which male birds were treated to a single oral dose of 316 mg 

triazole/kg bird. No mortality was observed and there was no indication of reproductive 

effects. This report has not yet been reviewed. In addition, this protocol is not 

comparable to the standard submitted avian reproduction study. 

80
Table 4.8 Avian Chronic Toxicity Data 

Common 

Name

%AI Study Parameters NOAEC/LOAEC MRID Classification/

Category

Bobwhite 

Quail 

Colinus 

virginianus

94.2 Reproduction study 

Mean measured 

concentrations: 0 

(vehicle), 72.5, 124.2, 

181.8, 255.8 ppm for 22 

consecutive weeks to 18 

week old quail. 

16 pairs per 

concentration level 

NOAEC = 256 ppm1

LOAEC >256 ppm 

No treatment-related 

effects at any level. 

Not tested at 

sufficiently high 

concentration levels 

43087901 Supplemental 

Mallard Duck 

Anas 

platyrhynchos

94.2 Reproduction study 

Mean measured 

concentrations: 0 

(vehicle), 72.5, 124.2, 

181.8, 255.8 ppm for 22 

consecutive weeks to 17 

week old ducks. 

16 pairs per 

concentration level 

NOAEC = 256 ppm 

LOAEC >256 ppm 

No treatment-related 

effects at any level. 

Not tested at 

sufficiently high 

concentration levels 

43087902 Supplemental 

1 Bold value is the value that will be used to calculate risk quotients 

4.2.1.3 Birds: Sublethal Effects and Additional Open Literature 

In the acute oral toxicity study for the bobwhite quail (MRID 00144286), it was reported 

that the test organisms exhibited lethargy and anorexia at all dose levels. The LOAEL for 

this study was 316 mg/kg (lowest dose tested). The NOAEL was not determined for 

sublethal effects. In the mallard duck subacute dietary study used for risk estimation 

(MRID 00144288), anorexia and lethargy were observed in birds at and above 2500 ppm 

starting at day two and ending on day 4. After day four all birds appeared normal. The 

NOAEC was 1250 ppm. The subacute dietary study with bobwhite quail also exhibited 

anorexia and lethargy at 3000 and 4530 ppm. There were no avian studies available in 

the ECOTOX open literature for myclobutanil. 

4.2.2 Toxicity to Mammals 

Mammalian toxicity data are used to assess potential indirect effects of myclobutanil to 

the terrestrial-phase CRLF. Effects to small mammals resulting from exposure to 

myclobutanil could indirectly affect the CRLF via reduction in available food. As 

discussed in Section 2.5.3, over 50% of the prey mass of the CRLF may consist of 

vertebrates such as mice, frogs, and fish (Hayes and Tennant 1985). 

 

81
4.2.2.1 Mammals: Acute Exposure (Mortality) Studies 

Available acute toxicity data for the TGAI and several formulations with the mouse and 

rat are available for myclobutanil. The available data suggest that myclobutanil is 

slightly toxic to small mammals on an acute oral basis (Appendices J and K). The most 

sensitive endpoint for the TGAI, the mouse LD50 of 1360 mg/kg, will be used to estimate 

risk to the CRLF via indirect effects to mammals. The probit dose-response slope for this 

study is 1.19 with no confidence interval provided. 

Acute toxicity data with the mouse on the 1,2,4-triazole degradate indicates that it is not 

more acutely toxic than the parent. The acute LD50 is 3650 mg/kg bw (MRID 45284001). 

With the exception of the 60 DF formulation, the myclobutanil formulations, including 

those mixed with other pesticides are not more acutely toxic to mammals than the 

technical material. The 60 DF formulation has a rat LD50 of 980 mg formulation/kg bw 

and may therefore be more toxic than the technical material but still falls within the 

category of slightly toxic. Risk estimations are conducted for the 60 DF formulation with 

the rat to ensure that the assessment is protective of acute mammalian exposure to the DF 

formulation. 

Table 4.9 Mammalian Acute Toxicity Data 

Common 

Name

%AI Study parameters LD50 /NOAEL MRID Classification/

Category

Laboratory 

mouse 

Mus 

musculus 

91.9 Acute oral study 

0, 1.3, 2.0, 3.2, 5.0 

g/kg bw tested 

10/dose level 

14-day observation 

period 

Acute oral LD50=1360 

mg/kg bw in female mice 

(most sensitive species 

(original DER mistakenly 

stated that it was in the 

rat)). Mortality at all 

dose levels tested. 

Multiple clinical signs, 

including ataxia, tremors, 

loss of righting and others 

– not dose-related; 

however, early deaths 

may have affected 

reporting. 

Probit slope: 1.19. 

00165239 

00141662 

Acceptable 

Slightly toxic1 

Laboratory 

mouse 

Mus 

musculus

1,2,4-

triazole 

Acute oral study LD50 = 3650 mg/kg 45284001 Practically 

nontoxic 

1

 Based on LD50 (mg/kg) <10 very highly toxic; 10-50 highly toxic; 51-500 moderately toxic; 501-2000 

slightly toxic; >2000 practically nontoxic 

2 Bold value is the value that will be used to calculate risk quotients 

82
Table 4.10 Acute Rat Toxicity Comparison of Myclobutanil Formulations 

Formulation (%) LD50 (mg/kg bw) MRID 

Technical Product 1600 (M) 

2290 (F) 

00141662 

1.5% with 2.5% permethrin > 5050 (M & F) 44155803 

2.25% with 60% mancozeb > 5000 (M) 40149003 

60% formulation with inerts 980 (M) 

1235 (F) 

00164467, 00164468 

Fludioxonil, 1.45%; Mefenoxam, 3.61%; 

Azoxystrobin, 8.55%; and Myclobutanil, 9.75% 

5979 (F) 47092603 

Up-and-Down Method: 0.9% Myclobutanil (granules) > 5000 (F) 46886701 

1% formulation > 5000 (M & F) 45381001 

21% formulation 3749 (F) 

 >5000 (M) 

45218401 

6.0% formulation LD50 between 500 & 

5,000 (M & F) 

45056903 

1% formulation > 5,000 (M & F) 44265201 

4.2.2.2 Mammals: Chronic Exposure (Growth, Reproduction) Studies 

In a two-generation reproduction study in rats on myclobutanil (MRIDs 00149581 and 

00143766), the NOAEC/NOAEL used in the assessment is 200 ppm/16 mg/kg bw/day 

with a LOAEC/LOAEL of 1000 ppm/80 mg/kg bw/day based on a decrease in pup body 

weight gain during lactation, an increased incidence in the number of stillborns and 

atrophy of the testes and prostate (offspring systemic and reproductive endpoints). These 

endpoints were used in the risk assessment because the parental systemic toxicity 

endpoints are not considered to be relevant to either growth or reproductive effects 

(MRID 00149581). 

As previously noted, RH-9090 is a major metabolite of myclobutanil. It is considered to 

be of equivalent toxicity to the parent based on SAR and tolerances for myclobutanil 

residues in food are established for the combined residues of myclobutanil and RH-9090 

on registered commodities. 

In addition, 1,2,4-triazole and triazole conjugates (triazole alanine and triazole acetic 

acid) are common degradates of triazole compounds, including myclobutanil. The 1,2,4-

triazole degradate was tested in a two-generation reproduction study (MRID 46467304). 

The parental NOAEL/LOAEL is <15 mg/kg bw/day/15 mg/kg bw/day based on a 

decrease in bodyweight and bodyweight gain and decrease in spleen weight. The 

offspring NOAEL/LOAEL is <19 mg/kg bw/day/19 mg/kg bw/day based on decrease in 

bodyweight and bodyweight gain and brain and spleen weight. The reproductive 

NOAEL/LOAEL is 15/31 mg/kg bw/day based on abnormal sperm and a decrease in the 

number of corpora lutea. At 218 mg/kg bw/day, there was reproductive failure (no viable 

offspring) and an increase in corpora lutea in F0 parental females. A comparison of the 

endpoints between the parent and the degradate, indicates that the degradate may have a 

greater effect on bodyweight and bodyweight gain for both parents and pups; however, 

83
the endpoint values for reproductive effects for the parent are equivalent to the degradate. 

There is an uncertainty due to dose spacing; however, the results indicate that the 

degradate is at least as toxic as the parent. 

Toxicity data are also available for the degradate triazole alanine. Other triazole 

conjugates are considered to be toxicologically equivalent to triazole alanine. 

A two-generation rat reproduction study conducted on triazole alanine (MRID 00164112) 

indicates that the triazole conjugates exhibit less toxicity than the parent. 

Maternal/parental toxicity was not seen in the rat reproduction study at the highest dose 

tested (929/988 M/F mg/kg bw/day). Reproductive toxicity was also not seen at the 

highest dose tested. The offspring NOAEL/LOAEL is 192/929 mg/kg bw/day based on 

reduced mean litter weights in both generations. 

Since 1,2,4-triazole and triazole conjugates are common degradates of triazole 

compounds and the mechanism of toxicity of these compounds is considered to be 

fundamentally different than the toxicity for the parent triazoles (e.g., myclobutanil), 

separate human health risk assessments have been conducted for 1,2,4-triazole and 

triazole conjugates. (February 7, 2006, 1,2,4-Triazole, Triazole Alanine, Triazole Acetic 

Acid: Human Health Aggregate Risk Assessment in Support of Reregistration and 

Registration Actions for Triazole-derivative Fungicide Compounds DP322215). 

4.2.2.3 Mammals: Open Literature 

A review of mammalian studies available in the ECOTOX open literature for 

myclobutanil indicates that no additional toxicity data relevant to the myclobutanil CRLF 

assessment were provided in the open literature i.e., none of the available mammalian 

studies identified a more sensitive endpoint. Therefore, only toxicity data provided in 

submitted studies were used to assess mammalian effects. 

84
Table 4.11 Mammalian Chronic Toxicity Data 

Common 

Name

%AI Study Parameters NOAEC/ 

LOAEC

MRID Classification/

Category

Laboratory 

rat 

Rattus 

norvegicus

84.5 2-Generation 

reproduction study 

25 rats/sex/group 

0, 50, 200 or 1000 

ppm 

4, 16 or 80 mg/kg 

bw/day based on 

overall mean 

concentration of 

active ingredient in 

dietary analyses. 

Parental 

NOAEC/NOAEL: 50 

ppm/4 mg/kg bw/day 

Parental 

LOAEC/LOAEL: 200 

ppm/16 mg/kg bw/day 

based on hepatocellular 

hypertrophy and increases 

in liver weights.

Offspring/Reproductive 

NOAEC/NOAEL: 200 

ppm/16 mg/kg/day 

Offspring/Reproductive 

LOAEC/LOAEL: 1000 

ppm/80 mg/kg/day based 

on testicular, epididymal 

and prostatic atrophy in 

P2 males; slight increase 

in stillborns, decrease in 

body weight gain in pups 

during lactation in F1 and 

F2 generations. 

00149581 

00143766 

Acceptable 

85
Common %AI Study Parameters NOAEC/ MRID Classification/

Name LOAEC Category

Laboratory 

rat 

Rattus 

norvegicus

1,2,4- 

triazole 

Reproduction and 

fertility effects

0, 250, 500, 3000 

ppm 

M: 15, 31, 189 mkd 

F: 18, 36, 218 mkd 

Parental 

NOAEC/NOAEL: <250 

ppm/15 mg/kg/day 

Parental 

LOAEC/LOAEL: 250 

ppm/15 mg/kg/day based 

on decrease in 

bodyweight, bodyweight 

gain and spleen weight. 

Offspring 

NOAEC/NOAEL: <250 

ppm/19 mg/kg/day 

Offspring 

LOAEC/LOAEL: 250 

ppm/19 mg/kg/day based 

on decrease in 

bodyweight, bodyweight 

gain, brain and spleen 

weights Repro 

NOAEC/NOAEL: 250 

ppm/15 mg/kg/day 

Repro LOAEC/LOAEL: 

500 ppm/31 mg/kg/day 

based on abnormal sperm 

and ↓# of CL in F1

females 

At 3000 ppm/218 

mg/kg/day, reproductive 

failure (no viable 

offspring), ↑CL in F0

parental females 

46467304 Acceptable 

Laboratory 

rat 

Rattus 

norvegicus

Triazole 

Alanine 

Reproduction and 

fertility effects

0, 200, 2000, 10000 

ppm 

M: (F0/F1) 0, 

50/47, 213/192, 

1098/929 

mg/kg/day 

F: 0, 51/49, 

223/199, 1109/988 

mg/kg/day 

Parental 

NOAEC/NOAEL: 10000 

ppm/929 mg/kg/day 

Parental 

LOAEC/LOAEL: >10000 

ppm/929mg/kg/day 

Offspring 

NOAEC/NOAEL: <250 

ppm/19 mg/kg/day 

Offspring 

LOAEC/LOAEL: 

2000ppm/192 mg/kg/day 

based on reduced mean 

litter weights in both 

generations 

 Repro LOAEC/LOAEL: 

>10000 

ppm/929mg/kg/day 

00164112 Acceptable 

1 Bold value is the value that will be used to calculate risk quotients 

86
4.2.3 Toxicity to Terrestrial Invertebrates 

Terrestrial invertebrate toxicity data are used to assess potential indirect effects of 

myclobutanil to the terrestrial-phase CRLF. Effects to terrestrial invertebrates resulting 

from exposure to myclobutanil could indirectly affect the CRLF via reduction in 

available food. 

4.2.3.1 Terrestrial Invertebrates: Acute Exposure (Mortality) Studies 

Myclobutanil is classified as non-toxic to bees with an acute contact LD50 of >362 

μg/bee (MRID 00144289). The bees were exposed to a finished dust containing 27.58% 

a.i. in a bell jar vacuum duster at dosages of approximately 120, 240 or 362 μg technical 

material per bee. Observations for clinical signs of toxicity were made daily for at 24 

hour intervals from 24 to 96 hours. Mortality in the treated bees did not differ from the 

untreated controls. 

4.2.3.2 Terrestrial Invertebrates: Open Literature Studies 

There are several terrestrial invertebrate toxicity studies available in the open literature 

(Appendices H and I). Five acceptable literature studies were reviewed for this 

assessment; one study on beneficial arthropods, three studies on predacious mites and one 

study on mirids, a predacious insect (EcoReference Nos.: 104765, 96453, 64063, 63621, 

63599). These studies were used qualitatively as part of a weight of the evidence 

analysis/determination. The arthropods study showed myclobutanil to be harmless to all 

of the five arthropods tested including, parasitic wasps, lady-birds, hoverfly, rove beetle, 

and carabid beetle. The three mite studies showed no adverse effects on the four species 

evaluated. In the study on the mired, myclobutanil showed moderate toxicity (LD50 = 

150 μg ai/L) to adult mirid at the manufacturer’s label rate of 440 μg ai/L but no toxicity 

to nymphs. 

Although one of the available open literature studies identified a more sensitive endpoint 

than the submitted honey bee toxicity study that determined a dust LD50 of > 100 μg/bee, 

the weight of the evidence indicates that myclobutanil is non-toxic to terrestrial 

invertebrates. Four of the five studies clearly showed that myclobutanil was not toxic to 

terrestrial invertebrates at label rates. Only one of the five available acceptable studies 

provided an LD50. That study indicated moderate toxicity to adult mirids only with no 

toxicity to the nymphs. Myclobutanil toxicity to adults was unexpected because 

myclobutanil was seen to be innocuous to all stages of mites in three literature studies 

and mites are usually more easily intoxicated than insects (mirids). Therefore, based on 

the totality of the available data, the honey bee study represents the most appropriate 

study for endpoint selection. 

4.2.4 Toxicity to Terrestrial Plants 

Terrestrial plant toxicity data are used to evaluate the potential for myclobutanil to affect 

riparian zone and upland vegetation within the action area for the CRLF. Impacts to 

87
riparian and upland (i.e., grassland, woodland) vegetation could result in indirect effects 

to both aquatic- and terrestrial-phase CRLFs, as well as effects to designated critical 

habitat PCEs via increased sedimentation, alteration in water quality, and reduction of 

upland and riparian habitat that provides shelter, foraging, predator avoidance and 

dispersal for juvenile and adult CRLFs. 

There are currently no registrant-submitted terrestrial plant toxicity data for myclobutanil 

with which to assess the potential for indirect effects to the aquatic- and terrestrial-phase 

CRLF via effects to riparian vegetation or effects to the primary constituent elements 

(PCEs) relevant to the aquatic- and terrestrial-phase CRLF. However, there is some 

evidence in the open literature that myclobutanil has the potential to elicit phytotoxic 

effects. Three terrestrial plant studies were reviewed for this assessment. No adverse 

effects were observed in two of the three studies (EcoReference Nos.: 104715, 104728, 

76524). In a cucumber study, myclobutanil sprayed onto seedlings at the first true leaf 

(application rate not provided) did not affect fruit quality. In a seed treatment study, 

infected spring wheat treated with myclobutanil at a rate of 0.12 g/ ai./kg seed performed 

similarly to untreated seed. In the third study, myclobutanil was applied at two rates (6.1 

g ai/100 m2

 (0.54 lbs/A) and 12.19 g/ai 100 m2 (1.09 lbs/A)) to “Tifgreen” Bermuda grass 

to determine if it would produce a plant growth regulation effect on healthy Bermuda 

grass. After three applications at 28 to 30 day intervals, compared to the control, the high 

rate of myclobutanil significantly decreased turf grass quality on at least one evaluation 

date in each year of the study. 

In order to characterize potential effects to terrestrial plants following exposure to 

myclobutanil in the risk description, terrestrial plant data from 5 other triazole DMI 

fungicides were obtained and used as inputs values in the TerrPlant (v. 1.2.2) model for 

terrestrial plants. Table 4.12 summarizes the toxicity values and endpoints for the 5 

triazole fungicides. 

Table 4.12 Terrestrial Plant Toxicity Data for 5 Other DMI Fungicides 

Fungicide EC25 (lbs a.i./A) NOAEC/EC05 (lbs 

a.i./A) 

Effect/MRID 

Seedling 

Emergence 

Vegetative 

Vigor 

Seedling 

Emergence 

Vegetative 

Vigor 

Seedling 

Emergence 

Vegetative 

Vigor 

Metconazole 

Monocot 0.78 >0.6 0.3 0.6 Ryegrass: 

reduced 

plant height 

46805103 

46805104 

Dicot 0.15 0.44 0.075 0.0036 

(EC05) 

Radish: 

reduced 

plant height 

46805103 

Radish: 

reduced dry 

weight 

46805104 

Prothioconazole 

Monocot >0.272 >0.272 0.272 0.272 46246049 46246049 

Dicot >0.272 >0.272 0.03 <0.272 Cucumber: 

shoot height 

and dry 

46246049 

88
Fungicide EC25 (lbs a.i./A) NOAEC/EC05 (lbs Effect/MRID 

a.i./A) 

Seedling 

Emergence 

Vegetative 

Vigor 

Seedling 

Emergence 

Vegetative 

Vigor 

Seedling 

Emergence 

Vegetative 

Vigor 

weight 

46246049 

Cyproconazole 

Monocot >0.64 >0.62 0.64 0.62 46218512 46218511 

Dicot 0.091 0.50 0.066 0.09 Cabbage: 

fresh weight 

46218512 

Cabbage: dry 

weight 

46218511 

Propiconazole 

Monocot > 1.5 0.315 1.5 0.0815 41673201 Rye grass: 

plant height 

41673203 

Dicot 0.18 0.039 0.056 0.056 Cabbage: 

dry weight 

41673201 

Cabbage: dry 

weight 

41673203 

Triticonazole 

Monocot >4.25 >4.2 1.3 4.2 Rye grass: 

shoot length 

44802116 

44802116 

Dicot 0.015 1.3 0.004 1.0 Lettuce: 

shoot length 

44802116 

Turnip: dry 

weight 

44802116 

4.3 Use of Probit Slope Response Relationship to Provide Information on the 

Endangered Species Levels of Concern 

The Agency uses the probit dose response relationship as a tool for providing additional 

information on the potential for acute direct effects to individual listed species and 

aquatic animals that may indirectly affect the listed species of concern (U.S. EPA, 2004). 

As part of the risk characterization, an interpretation of acute RQ for listed species is 

discussed. This interpretation is presented in terms of the chance of an individual event 

(i.e., mortality or immobilization) should exposure at the EEC actually occur for a species 

with sensitivity to myclobutanil on par with the acute toxicity endpoint selected for RQ 

calculation. To accomplish this interpretation, the Agency uses the slope of the dose 

response relationship available from the toxicity study used to establish the acute toxicity 

measures of effect for each taxonomic group that is relevant to this assessment. The 

individual effects probability associated with the acute RQ is based on the mean estimate 

of the slope and an assumption of a probit dose response relationship. In addition to a 

single effects probability estimate based on the mean, upper and lower estimates of the 

effects probability are also provided to account for variance in the slope, if available. 

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1 

(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP, 

Environmental Fate and Effects Division (June 22, 2004). The model allows for such 

calculations by entering the mean slope estimate (and the 95% confidence bounds of that 

89
estimate) as the slope parameter for the spreadsheet. In addition, the acute RQ is entered 

as the desired threshold. 

4.4 Incident Database Review 

A review of the EIIS database for ecological incidents involving myclobutanil was 

completed on May 26, 2009. Three incident reports were filed for myclobutanil between 

1994 and 2003, all with effects on terrestrial plants (two incidents with grapes and one 

with roses). The two incidents with grapes occurred in California and the one with roses 

was reported in Maryland. The certainty index for the damage in all 3 incidents was 

rated as possibly related to exposure to myclobutanil. The two incidents with grapes 

involved application of other pesticides as well as the myclobutanil. Therefore, it is 

unclear whether the effects were due to exposure to myclobutanil in these two incidents. 

Myclobutanil was the only pesticide applied to the rose bushes in the third reported 

incident. A brief description of each of the reported incidents is provided below. 

It should be noted that these reported incidents may only represent a fraction of actual 

incidents. Actual incidents may not have been reported due to various factors such as 

lack of reporting, or a lack of witness to effects. Therefore, the lack of an incident report 

does not necessarily indicate a lack of an incident. 

Complete incident tables are provided in Appendix L. 

4.4.1 Terrestrial Incidents 

Between 5/30/1994 and 6/3/1994, Rally 40W (myclobutanil), Pro Gibb (gibberellic acid), 

Dimethogan 25 WP, Pro Kil Cryolite 96 (sodium fluoaluminate), Britz binder, and 

Booster 42 Foliar Spray (polymeric polyhydroxy acids) were applied by ground spray to 

grape vines. Shortly after the last application, scarring of the berries, stunted vine 

growth, lack of berry size increase, dieback of fruit from total bunches, and limited cone 

growth with straggly branches were observed. No residue analysis was conducted. The 

California Commissioner’s report indicated that mixtures of Pro-Gibb 4% and Pro-Kil 

Cryolite 96 may cause some compatibility problems. The certainty index for this incident 

(I002621-006) is possible. 

It was reported that Rally 40W (myclobutanil) damaged 6 acres of Red Globe and 

Thompson’s grapes to the point that they could not be sold. Burns and necrosis on 

bunches (Red Globe) and leaf burn (Thompson’s) was observed. AGRI-MEK 

(abamectin) and Ad-Wet were also applied, using a ground spray on the vineyard. The 

certainty index for this incident (I013563-014) is possible. 

Systhane (myclobutanil) was applied via a broadcast ground spray to rose bushes grown 

in greenhouses by local residents in Maryland. The total magnitude was 200 houses. 

Foliar necrosis and some defoliation were observed after exposure to Systhane. Damage 

varied from house to house and by rose variety. The certainty index for this incident 

(I014702-074) is possible. 

90
No incidents involving terrestrial animals were reported. 

4.4.2 Aquatic Incidents 

No incidents involving aquatic plants or animals were reported. 

5 Risk Characterization 

Risk characterization is the integration of the exposure and effects characterizations. 

Risk characterization is used to determine the potential for direct and/or indirect effects to 

the CRLF or to its designated critical habitat from the use of myclobutanil in CA. The 

risk characterization provides an estimation (Section 5.1) and a description (Section 5.2) 

of the likelihood of adverse effects; articulates risk assessment assumptions, limitations, 

and uncertainties; and synthesizes an overall conclusion regarding the likelihood of 

adverse effects to the CRLF or its designated critical habitat (i.e., “no effect,” “likely to 

adversely affect,” or “may affect, but not likely to adversely affect”). 

5.1 Risk Estimation 

Risk is estimated by calculating the ratio of exposure to toxicity. This ratio is the risk 

quotient (RQ), which is then compared to pre-established acute and chronic levels of 

concern (LOCs) for each category evaluated (Appendix F). For acute exposures to the 

CRLF and its animal prey in aquatic habitats, as well as terrestrial invertebrates, the LOC 

is 0.05. For acute exposures to the CRLF and mammals, the LOC is 0.1. The LOC for 

chronic exposures to CRLF and its prey, as well as acute exposures to plants is 1.0. 

Risk to the aquatic-phase CRLF is estimated by calculating the ratio of exposure to 

toxicity using 1-in-10 year EECs based on the label-recommended myclobutanil usage 

scenarios summarized in Tables 3.5 and 3.6 and the appropriate aquatic toxicity endpoint 

from Table 4.1. Risks to the terrestrial-phase CRLF and its prey (e.g. terrestrial insects, 

small mammals and terrestrial-phase frogs) are estimated based on exposures resulting 

from applications of myclobutanil (Tables 3.9 – 3.10) and the appropriate toxicity 

endpoint from Table 4.5. Due to lack of toxicity data for myclobutanil, exposures are not 

estimated for freshwater invertebrates (chronic exposure), aquatic vascular plants, and 

terrestrial plants. 

5.1.1 Exposures in the Aquatic Habitat 

Estimated risk for the aquatic habitat is based on a total toxicity approach, that is, EECs 

for myclobutanil plus 1,2,4-triazole (parent plus degradate) which are higher than the 

EECs for myclobutanil. There are no aquatic toxicity data available for the primary 

degradate of myclobutanil (1,2,4-triazole); however, available mammalian studies 

indicate that it is either less than or equally toxic as the parent. Use of the total toxicity 

91
approach for estimating risk was based on two conservative assumptions. First, that the 

mode of action is the same for 1,2,4-triazole and the parent (myclobutanil) and second 

that the two compounds are of equivalent toxicity to aquatic organisms. 

5.1.1.1 Direct Effects to Aquatic-Phase CRLF 

Direct acute effects to the aquatic-phase CRLF are based on peak EECs from the 

PRZM/EXAMS models and the lowest acute 96-hour LC50 toxicity value for freshwater 

fish. The highest modeled peak EEC is 61.41 ppb (myclobutanil plus 1,2,4 triazole) for 

the turf scenario (representing turf use). The acute RQ for this scenario is 0.025 which is 

lower than the acute endangered species LOC of 0.05. 

In order to assess direct chronic risks to the CRLF, 60-day EECs from the 

PRZM/EXAMS models and the lowest chronic toxicity value (NOAEC) for freshwater 

fish are used. The highest modeled 60-day EEC is 60.71 ppb (myclobutanil plus 1,2,4 

triazole) for the turf scenario. The chronic RQ for this scenario is 0.061 which is much 

lower than the chronic LOC of 1 for fish. 

Acute and chronic RQs for all modeled scenarios for myclobutanil and myclobutanil plus 

1,2,4 triazole were lower than the related LOC (a summary of the highest RQs is 

provided in Table 5.1). Based on these results, the effects determination for myclobutanil 

is “no effect” for direct effects on the aquatic-phase of the CRLF. 

Table 5.1 Summary of Acute and Chronic Direct Effect RQs for the Aquatic-phase 

CRLF 

Direct Effects 

to CRLF

Scenario EEC (μg/L) c RQ Probability of 

Individual Effect 

at 

ES LOCd, e

Probability of 

Individual Effect 

at RQd

Acute Direct 

Toxicity a

Turf Peak: 61.41 0.025f ~1 in 4.18E+8 

(~1 in 216 to 

~1 in 1.75E+31)

~1 in 3.56E+12 

(~1 in 1.48E+3 to 

~1 in 5.06E+46)

Chronic Direct 

Toxicity b

Turf 60-day: 60.71 0.061g Not calculated for chronic endpoints 

a

 Based on bluegill sunfish (Lepomis macrochirus) acute 96-hour LC50 = 2.4 mg/L. b

 Based on fathead minnow (Pimephales promelas) chronic NOAEC = 0.98 mg/L. c

 From scenario with the highest EECs: granular use on turf (myclobutanil plus 1,2,4-triazole) (see Table 3.6). 

d

 The probit dose-response slope value for the bluegill sunfish acute toxicity study is not available; therefore, 

the effect probability was calculated based on a default slope assumption of 4.5 with upper and lower 95% 

confidence intervals of 2 and 9 (Urban and Cook, 1986). 

e

 Endangered species LOC of 0.05. 

f

 RQ < acute endangered species LOC of 0.05. 

g RQ < chronic LOC of 1. 

92
5.1.1.2 Indirect Effects to Aquatic-Phase CRLF via Reduction in Prey 

(non-vascular aquatic plants, aquatic invertebrates, fish, and 

frogs) 

a) Non-vascular Aquatic Plants

Indirect effects of myclobutanil to the aquatic-phase CRLF (tadpoles) via reduction in 

non-vascular aquatic plants in its diet are based on peak EECs from the PRZM/EXAMS 

models and the lowest toxicity value (EC50) for aquatic non-vascular plants. The most 

sensitive non-vascular plant 120-hour EC50 is 0.83 mg/L (freshwater green algae). The 

highest modeled peak EEC is 61.41 ppb (myclobutanil plus 1,2,4 triazole) for the turf 

scenario (representing turf use). The acute RQ for this scenario is 0.074 (61.41 ppb / 830 

ppb) which is much lower than the LOC of 1 for aquatic plants. 

RQs for all modeled scenarios for myclobutanil and myclobutanil plus 1,2,4 triazole were 

lower than the aquatic plant LOC. Based on these results, the effects determination for 

myclobutanil is “no effect” for indirect effects on the CRLF via reduction in non-vascular 

plants. 

b) Aquatic Invertebrates

Indirect acute effects to the aquatic-phase CRLF via effects to prey (invertebrates) in 

aquatic habitats are based on peak EECs from the PRZM/EXAMS models and the lowest 

acute toxicity value (LC50) for freshwater invertebrates. The highest modeled peak EEC 

is 61.41 ppb (myclobutanil plus 1,2,4 triazole) for the turf scenario (representing turf 

use). The acute RQ for this scenario is 0.005 which is much lower than the acute 

endangered species LOC of 0.05. 

Indirect chronic effects to the aquatic-phase CRLF via effects to prey (invertebrates) 

cannot be quantitatively estimated because there is currently no chronic invertebrate 

toxicity data available for myclobutanil. 

Acute RQs for all modeled scenarios for myclobutanil and myclobutanil plus 1,2,4 

triazole were lower than the endangered species LOC of 0.05 (a summary of the highest 

RQ is provided in Table 5.2). Based on these results, on an acute basis the effects 

determination for myclobutanil is “no effect” for indirect effects on the CRLF via 

reduction in freshwater invertebrates prey items. 

93
Table 5.2 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to 

the CRLF via Direct Effects on Aquatic Invertebrates as Dietary Food Items (prey 

of CRLF juveniles and adults in aquatic habitats) 

Direct Effects 

to Aquatic 

Invertebrate 

Prey of 

CRLF

Scenario EEC (μg/L) b RQ % Expected Effect on Prey Population 

at RQc 

Acute Direct 

Toxicity a

Turf Peak: 61.41 0.005d <0.001 (<0.001 - <0.001) 

Chronic Direct 

Toxicity

Not calculated (no toxicity data available) 

a

 Based on water flea (Daphnia magna) acute 48-hour LC50 = 11 mg/L. b

 From scenario with the highest EECs: granular use on turf (myclobutanil plus 1,2,4-triazole) (see Table 3.6) 

c

 The % expected effect on prey population was calculated based on a probit dose-response slope of 6.8 (4.1-

9.6) for the water flea acute toxicity study. 

d

 RQ < acute endangered species LOC of 0.05. 

c) Fish and Frogs

Fish and frogs also represent potential prey items of adult aquatic-phase CRLFs. RQs 

associated with acute and chronic direct toxicity to the CRLF (Table 5.1) are used to 

assess potential indirect effects to the CRLF based on a reduction in freshwater fish and 

frogs as food items. Based on the conclusions about direct effects to freshwater fish (see 

section 5.1.1.1), the effects determination for myclobutanil is “no effect” for indirect 

effects on the CRLF via reduction in freshwater fish and frogs as food items. 

5.1.1.3 Indirect Effects to CRLF via Reduction in Habitat and/or 

Primary Productivity (Freshwater Aquatic Plants) 

Indirect effects to the CRLF via direct toxicity to aquatic plants are estimated using the 

most sensitive non-vascular and vascular plant toxicity endpoints. The effects 

determination for myclobutanil is “no effect” for indirect effects on the CRLF via 

reduction in non-vascular plants (see section 5.1.1.2 for details). Effects to aquatic 

vascular plants cannot be quantitatively estimated because there is currently no toxicity 

data available for myclobutanil. 

5.1.2 Exposures in the Terrestrial Habitat 

5.1.2.1 Direct Effects to Terrestrial-phase CRLF 

As previously discussed in Section 3.3, potential direct effects to terrestrial-phase CRLFs 

are based on foliar and granular applications of myclobutanil. In addition, the RQ 

94
calculation for use on cotton seeds assumes that the seeds are 100% available based on 

shallow planting conditions and an associated planting depth of 1⁄2 inch. 

Potential direct acute effects to the terrestrial-phase CRLF are derived by considering 

dose- and dietary-based EECs modeled in T-REX for a small bird (20 g) consuming 

small invertebrates and acute oral and subacute dietary toxicity endpoints for avian 

species. Definitive subacute dietary-based RQ values cannot be derived because a 

statistically meaningful LC50 could not be determined as no dose levels resulted in 50% 

or greater mortality (i.e., mallard duck LC50 is > 4090 ppm). Although definitive LC50’s 

were not derived in the subacute dietary studies, there were mortalities in both studies. 

The concentration levels at which mortalities were observed will be compared to the 

terrestrial EECs in the Risk Description section. 

Results of the dose-based EEC analysis of direct effects to terrestrial-phase CRLF 

indicate acute LOC exceedances (RQ > 0.1) for all uses of myclobutanil except 

Boysenberry/Dewberry/Youngberry (Tables 5.3 and 5.4). 

Table 5.3 Summary of Acute RQs Used to Estimate Direct Effects to the 

Terrestrial-phase CRLF (non-granular application) 

Use Application Rate

(lb ai/A) 

Dose-based 

Acute RQ*1 

Probability of Individual 

Effect at RQ2

Almond 0.2 0.23 1 in ~ 2.77E+05

Apple 0.5 0.70 1 in ~ 7.24E+00

Apricot 0.5 0.40 1 in ~ 3.88E+02

Artichoke 0.1 0.14 1 in ~ 1.03E+09

Asparagus 0.125 0.18 1 in ~ 1.21E+07

Beans 0.125 0.18 1 in ~ 1.21E+07

Blackberry/EggPlant/Okra/Pepper/Raspberry 0.125 0.16 1 in ~ 9.04E+07

Boysenberry/Dewberry/Youngberry 0.0625 0.08 1 in ~ 1.54E+14

Carrot 0.1875 0.14 1 in ~ 1.03E+09

Canistel/Mango/Papaya/Sapodilla 0.25 0.39 1 in ~ 4.95E+02

Cherry/Nectarine/Peach 0.5 0.56 1 in ~ 2.61E+01

Cotton 0.06 lb ai/cwt 0.42 1 in ~ 2.47E+02 

Cucurbit Vegetables 0.12 0.20 1 in ~ 2.24E+06

Currant 0.125 0.19 1 in ~ 1.21E+07

Gooseberry 0.125 0.24 1 in ~ 1.52E+05

Grapes 0.13 0.24 1 in ~ 5.03E+06

Hops 0.25 0.35 1 in ~ 1.97E+04

Lettuce 0.125 0.15 1 in ~ 2.87E+08

Plum/Prune 0.16 0.33 1 in ~ 2.81E+03

Tomato 0.1 0.10 1 in ~9.62E+11

Turf 1.3 1.93 1 in ~ 1

* = LOC exceedances (acute RQ > 0.1) are bolded and shaded. 1

 Based on bobwhite quail acute oral LD50 of 498 mg/kg . 

2 The effect probability was calculated based on a calculated slope of 7.03 with upper and lower 95% confidence intervals of 

3.5 and 10.5

95
 

Table 5.4 Summary of Acute RQs Used to Estimate Direct Effects to the Terrestrialphase CRLF (granular application) 

Use Application Rate 

(lb ai/A) 

Dose-based Acute 

RQ*1 

Probability of Individual 

Effect at RQ 

Turf 1.35 1.96 1 in ~ 1

* = LOC exceedances (acute RQ > 0.1) are bolded and shaded. 1

 Based on bobwhite quail acute oral LD50 of 498 mg/kg and a calculated LD50/sq. ft 

Potential direct chronic effects of myclobutanil to the terrestrial-phase CRLF are derived 

by considering dietary-based exposures modeled in T-REX for a small bird (20g) 

consuming small invertebrates. Chronic effects are estimated using the lowest available 

toxicity data for birds. EECs are divided by toxicity values to estimate chronic dietarybased RQs. Results of the analysis of direct effects to terrestrial-phase CRLF indicate a 

chronic LOC exceedance (RQ>1) for turf and cotton use only. 

Based on the exceedance of the LOC for the majority of uses after acute exposure and 

two uses after chronic exposure, myclobutanil may affect directly, the terrestrial-phase of 

the CRLF. 

Table 5.5 Summary of Chronic RQs Used to Estimate Direct Effects to the 

Terrestrial-phase CRLF (non-granular application) 

Use Application Rate (lb ai/A) Dietary-based Chronic RQ*1 

Almond 0.2 0.28 

Apple 0.5 0.87 

Apricot 0.5 0.49 

Artichoke 0.1 0.18 

Asparagus 0.125 0.22 

Beans 0.125 0.22 

Blackberry/EggPlant/Okra/Pepper/Raspberry 0.125 0.20 

Boysenberry/Dewberry/Youngberry 0.0625 0.10 

Carrot 0.1875 0.17 

Canistel/Mango/Papaya/Sapodilla 0.25 0.49 

Cherry/Nectarine/Peach 0.5 0.69 

Cotton 0.06 lb ai/cwt 2.342 

Cucurbit Vegetables 0.12 0.24 

Currant 0.125 0.23 

Gooseberry 0.125 0.23 

Grapes 0.13 0.30 

Hops 0.25 0.43 

Lettuce 0.125 0.18 

Plum/Prune 0.16 0.40 

Tomato 0.1 0.13 

Turf 1.3 2.38 

* = LOC exceedances (chronic RQ > 1) are bolded and shaded. 1

 Based on bobwhite quail NOAEC of 256 ppm. 

2

 Planting depth for cotton seeds varies depending on soil moisture and soil texture. The RQ calculation assumes that cotton 

seeds are 100% available based on shallow planting conditions and an associated planting depth of 1⁄2 inch 

96
5.1.2.2 Indirect Effects to Terrestrial-Phase CRLF via Reduction in 

Prey (terrestrial invertebrates, mammals, and frogs) 

5.1.2.2.1 Terrestrial Invertebrates 

In order to assess the risks of myclobutanil to terrestrial invertebrates, which are 

considered prey of CRLF in terrestrial habitats, the honey bee is used as a surrogate for 

terrestrial invertebrates. The toxicity value for terrestrial invertebrates is calculated by 

multiplying the lowest available acute contact (dust) LD50 of > 363 μg a.i./bee by 1 

bee/0.128g, which is based on the weight of an adult honey bee. This is estimated to be 

>2836 μg a.i./g bw. Because the acute contact effects data shows an LD50 of greater than 

the highest test concentration of 363 μg a.i./bee, definitive acute RQ values cannot be 

derived. Therefore, a quantitative assessment of risk to terrestrial invertebrates was not 

conducted. Mortality in the treated bees did not differ from the untreated controls. Given 

that the honey bee data shows low toxicity, minimal potential indirect impact to the 

CRLF via effects of myclobutanil on freshwater invertebrate food items is expected. 

Risk to terrestrial invertebrates will be discussed further in the risk description section. 

5.1.2.2.2 Mammals 

Risks associated with ingestion of small mammals by large terrestrial-phase CRLFs are 

derived for dietary-based and dose-based exposures modeled in T-REX for a small 

mammal (15g) consuming short grass. Acute and chronic effects are estimated using the 

most sensitive mammalian toxicity data. EECs are divided by the toxicity value to 

estimate acute and chronic dose-based RQs as well as chronic dietary-based RQs. For 

granular applications the RQ is based on an estimated LD50 per square foot calculated 

based on application rate and toxicity. For non-granular applications, the acute listed 

species LOC of 0.1 is exceeded for apple, apricot, cherry/nectarine/peach, 

canistel/mango/papaya/sapodilla, hops, plum/prune, and turf uses. The chronic LOC of 1 

on a dose basis is exceeded for all uses and the chronic LOC on a dietary basis is 

exceeded for apples, apricots, canistel/mango/papaya/sapodilla, cherry/nectarine/peach, 

cotton, and turf. For granular uses, the acute listed species LOC is exceeded for turf. 

Based on both acute and chronic LOC exceedances for many uses, myclobutanil may 

affect indirectly, the terrestrial-phase CRLF via reduction in small mammal prey items. 

97
Table 5.6 Summary of Acute and Chronic RQs Used to Estimate Indirect Effects to 

the Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary Food 

Items (non-granular application) 

Use (Application Rate lb ai/acre) 

Dose-based 

Chronic 

RQ*1 

Dietarybased 

Chronic 

RQ*2 

Dosebased 

Acute 

RQ*3 

% Expected 

Effect on Prey 

Population at 

RQ 4

Almond (0.2) 3.42 0.63 0.08 9.6 

Apple (0.5) 10.7 1.97 0.25 23.7 

Apricot (0.5) 6.09 1.12 0.14 15.5 

Artichoke (0.1) 2.18 0.40 0.05 6.1 

Asparagus (0.125) 2.72 0.50 0.06 7.3 

Beans (0.125) 2.67 0.49 0.06 7.3 

Blackberry/EggPlant/Okra/Pepper/Raspberry ( 

0.125) 

2.48 0.46 0.06 7.3 

Boysenberry/Dewberry/Youngberry (0.0625) 1.24 0.23 0.03 3.5 

Carrot (0.1875) 2.14 0.40 0.05 6.1 

Canistel/Mango/Papaya/Sapodilla (0.25) 5.99 1.10 0.14 15.5 

Cherry/Nectarine/Peach (0.5) 8.55 1.58 0.20 20.3 

Cotton NA 3.00 NA NA 

Cucurbit Vegetables (0.12) 3.02 0.56 0.07 8.5 

Currant (0.125) 2.82 0.49 0.06 7.3 

Gooseberry (0.125) 3.60 0.66 0.08 9.6 

Grapes (0.13) 3.69 0.68 0.09 10.7 

Hops (0.25) 5.35 0.99 0.12 13.7 

Lettuce (0.125) 2.25 0.42 0.05 6.1 

Plum/Prune (0.16) 5.00 0.92 0.12 13.7 

Tomato (0.1) 1.55 0.29 0.04 4.8 

Turf (1.3) 29.35 5.41 0.68 42.1 

* = LOC exceedances (acute RQ > 0.1; chronic RQ > 1) are bolded and shaded 1

 Based on dose-based EEC and myclobutanil rat NOAEL = 16 mg/kg-bw. 2 Based on dietary-based EEC and myclobutanil rat NOAEC = 200 mg/kg-diet. 3

 Based on dose-based EEC and myclobutanil mouse acute oral LD50 = 1360 mg/kg-bw. 4

 % expected effect on prey population at RQ is calculated using the acute mouse toxicity study probit dose-response slope of 

1.19. No confidence interval was provided. 

Table 5.7 Summary of Acute RQs Used to Estimate Indirect Effects to the 

Terrestrial-phase CRLF via Direct Effects on Small Mammals as Dietary Food 

Items (granular application) 

Use Application Rate (lb ai/A) Dose-based Acute RQ*1 % Expected Effect on Prey 

Population at RQ 

Turf 1.35 0.63 40.2 

* = LOC exceedances (acute RQ > 0.1) are bolded and shaded. 1

 Based and adjusted LD50 of 1380 mg/kg and a calculated LD50/sq. ft 

5.1.2.2.3 Frogs 

An additional prey item of the adult terrestrial-phase CRLF is other species of frogs. In 

order to assess risks to these organisms, dietary-based and dose-based exposures modeled 

in T-REX for a small bird (20g) consuming small invertebrates are used. See Section 

5.1.2.1 and associated tables for results. The acute LOC for listed species is exceeded for 

98
the majority of myclobutanil uses. The chronic LOC is exceeded for cotton and turf. 

Therefore, following both acute and chronic exposure myclobutanil may affect indirectly, 

the CRLF via reduction in frogs as prey items. 

5.1.2.3 Indirect Effects to CRLF via Reduction in Terrestrial Plant 

Community (Riparian and Upland Habitat) 

Indirect effects to the CRLF via reduction in terrestrial plant community cannot be 

quantitatively estimated because there are no vegetative vigor or seedling emergence 

plant toxicity data available for myclobutanil. For a qualitative risk description, see 

Section 5.2.3.2. 

5.1.3 Primary Constituent Elements of Designated Critical Habitat 

For myclobutanil use, the assessment endpoints for designated critical habitat PCEs 

involve a reduction and/or modification of food sources necessary for normal growth and 

viability of aquatic-phase CRLFs, and/or a reduction and/or modification of food sources 

for terrestrial-phase juveniles and adults. Because these endpoints are also being 

assessed relative to the potential for indirect effects to aquatic- and terrestrial-phase 

CRLF, the effects determinations for indirect effects from the potential loss of food items 

are used as the basis of the effects determination for potential effects to designated 

critical habitat. 

5.1.3.1 Aquatic-Phase (Aquatic Breeding Habitat and Aquatic NonBreeding Habitat) 

Three of the four assessment endpoints for the aquatic-phase primary constituent 

elements (PCEs) of designated critical habitat for the CRLF are related to potential 

effects to aquatic and/or terrestrial plants: 

• Alteration of channel/pond morphology or geometry and/or increase in sediment 

deposition within the stream channel or pond: aquatic habitat (including riparian 

vegetation) provides for shelter, foraging, predator avoidance, and aquatic 

dispersal for juvenile and adult CRLFs. 

• Alteration in water chemistry/quality including temperature, turbidity, and 

oxygen content necessary for normal growth and viability of juvenile and adult 

CRLFs and their food source. 

• Reduction and/or modification of aquatic-based food sources for pre-metamorphs 

(e.g., algae). 

Based on the risk estimation for potential effects to aquatic non-vascular plants provided 

in Section 5.1.1.2, myclobutanil is expected to have no effect on aquatic-phase PCEs of 

99
designated habitat related to effects on aquatic non-vascular plants. The highest modeled 

peak EEC for turf use (61.41 ppb) and the most sensitive non-vascular plant endpoint 

(830 ppb) provide an aquatic non-vascular plant RQ of 0.074, which is much lower than 

the LOC of 1 for aquatic plants. Therefore, the RQs for all scenarios will be less than the 

LOC for aquatic plants. 

Risk estimations for potential effects to aquatic vascular plants and terrestrial plants were 

not conducted because no toxicity data are available for myclobutanil. Therefore, it 

cannot be estimated whether or not myclobutanil is likely to affect aquatic-phase PCEs of 

designated habitat related to effects on aquatic vascular plants and terrestrial plants. Risks 

to aquatic vascular plants and terrestrial plants will be discussed qualitatively in Section 

5.2.3. 

The remaining aquatic-phase PCE is “alteration of other chemical characteristics 

necessary for normal growth and viability of CRLFs and their food source.” To assess 

the impact of myclobutanil on this PCE (i.e., alteration of food sources), acute and 

chronic freshwater fish and invertebrate toxicity endpoints, as well endpoints for aquatic 

non-vascular plants, are used as measures of effects. RQs for these endpoints were 

calculated in Sections 5.1.1.1 and 5.1.1.2. Based on acute RQs for freshwater fish and 

invertebrates and for non-vascular plants that are less than the LOCs for all uses, 

myclobutanil is expected to have no effect on aquatic-phase PCEs of designated habitat 

related to effects of alteration of other chemical characteristics necessary for normal 

growth and viability of CRLFs and their food source. Following chronic exposure, data 

are only available for freshwater fish. For all uses, the chronic RQs for freshwater fish 

are less than the LOC. Therefore, following chronic exposure, it can only be partially 

estimated whether or not myclobutanil is likely to affect aquatic-phase PCEs of 

designated habitat related to effects of alteration of other chemical characteristics 

necessary for normal growth and viability of CRLFs and their food source. Based on 

chronic effects to freshwater fish, myclobutanil is expected to have no effect on this PCE. 

Chronic risk to freshwater invertebrates will be discussed qualitatively in section 5.2.2.2. 

5.1.3.2 Terrestrial-Phase (Upland Habitat and Dispersal Habitat)

The first two assessment endpoints for the terrestrial-phase PCEs of designated critical 

habitat for the CRLF are related to potential effects to terrestrial plants: 

• Elimination and/or disturbance of upland habitat; ability of habitat to support food 

source of CRLFs: Upland areas within 200 ft of the edge of the riparian 

vegetation or dripline surrounding aquatic and riparian habitat that are comprised 

of grasslands, woodlands, and/or wetland/riparian plant species that provides the 

CRLF shelter, forage, and predator avoidance 

• Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal 

habitat within designated units and between occupied locations within 0.7 mi of 

each other that allow for movement between sites including both natural and 

altered sites which do not contain barriers to dispersal 

100
The risk estimation for terrestrial-phase PCEs of designated habitat related to potential 

effects on terrestrial plants cannot be quantitatively addressed because there are no 

vegetative vigor or seedling emergence plant toxicity data available for myclobutanil. 

The risk will be discussed qualitatively in Section 5.2.3.2. 

The third terrestrial-phase PCE is “reduction and/or modification of food sources for 

terrestrial phase juveniles and adults.” To assess the impact of myclobutanil on this PCE, 

acute and chronic toxicity endpoints for birds, mammals, and terrestrial invertebrates are 

used as measures of effects. RQs for these endpoints were calculated in Sections 5.1.2.1 

and 5.1.2.2. For terrestrial-phase amphibians, using birds as a surrogate, there are acute 

LOC listed species exceedances for multiple uses. The chronic avian LOC is exceeded 

for turf and cotton uses. RQs for terrestrial invertebrates were not estimated because a 

definitive LD50 was not available. For mammals, the acute LOC for listed species is 

exceeded for multiple crops and the acute LOC for non-listed species is exceeded for turf. 

The chronic LOC is exceeded for multiple crops. Therefore, myclobutanil may affect the 

third terrestrial-phase PCE. 

The fourth terrestrial-phase PCE is based on alteration of chemical characteristics 

necessary for normal growth and viability of juvenile and adult CRLFs and their food 

source. Direct acute and chronic RQs for terrestrial-phase CRLFs are presented in 

Section 5.1.2.1. Again, the acute LOC is exceeded for multiple uses and the chronic 

LOC for cotton and turf uses. The same acute and chronic RQ estimates are used for 

indirect effects based on terrestrial-phase amphibians as a food source. For other prey 

species, RQs for terrestrial invertebrates were not estimated because a definitive LD50

was not available. For mammals, the acute LOC for listed species is exceeded for 

multiple crops and the acute LOC for non-listed species is exceeded for turf. The chronic 

LOC is exceeded for multiple crops. Therefore, myclobutanil may affect the fourth 

terrestrial-phase PCE. 

5.2 Risk Description 

The risk description synthesizes an overall conclusion regarding the likelihood of adverse 

impacts leading to an effects determination (i.e., “no effect,” “may affect, but not likely 

to adversely affect,” or “likely to adversely affect”) for the CRLF and its designated 

critical habitat. 

Based on the RQs presented in the Risk Estimation (Section 5.1) a preliminary effects 

determination is may affect for the CRLF and critical habitat. 

Direct/indirect effect LOCs are exceeded and myclobutanil use may affect the PCEs of 

the CRLF’s critical habitat. Therefore, the Agency concludes a preliminary “may 

affect” determination for the FIFRA regulatory action regarding myclobutanil. A 

summary of the risk estimation results are provided in Table 5.8 for direct and indirect 

effects to the CRLF and in Table 5.9 for the PCEs of designated critical habitat for the 

CRLF.

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Table 5.8 Risk Estimation Summary for Myclobutanil - Direct and Indirect Effects 

to CRLF 

Assessment Endpoint 

LOC 

Exceedances 

(Y/N) 

Description of Results of Risk Estimation 

Aquatic Phase 

(eggs, larvae, tadpoles, juveniles, and adults)

Direct Effects 

Survival, growth, and reproduction 

of CRLF individuals via direct 

effects on aquatic phases 

N There are no LOC exceedences for listed species following 

both acute and chronic exposure using freshwater fish as the 

surrogate for aquatic-phase amphibians. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects to 

food supply (i.e., freshwater 

invertebrates, non-vascular plants) 

Unknown There are no LOC exceedences for listed species following 

acute exposure to freshwater invertebrates. No chronic 

exposure data are available. A qualitative discussion of risk is 

provided. There are no LOC exceedences for aquatic nonvascular plants. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

habitat, cover, and/or primary 

productivity (i.e., aquatic plant 

community) 

Unknown There are no LOC exceedences for aquatic non-vascular plants. 

No aquatic vascular plant data are available. A qualitative 

discussion of risk is provided. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects to 

riparian vegetation, required to 

maintain acceptable water quality 

and habitat in ponds and streams 

comprising the species’ current 

range. 

Unknown No vegetative vigor or seedling emergence plant toxicity data 

are available. A qualitative discussion of risk is provided. 

Terrestrial Phase 

(Juveniles and adults)

Direct Effects 

Survival, growth, and reproduction 

of CRLF individuals via direct 

effects on terrestrial phase adults and 

juveniles 

Y For the terrestrial-phase CRLF, birds are used as a surrogate. 

There are dose-based acute LOC exceedances (RQ > 0.1) for all 

uses except Boysenberry/Dewberry/Youngberry. The chronic 

avian LOC is exceeded for turf and cotton uses. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

prey (i.e., terrestrial invertebrates, 

small terrestrial mammals and 

terrestrial phase amphibians) 

Y For mammals following non-granular applications, the acute 

listed species LOC is exceeded for apple, apricot, cherry, 

nectarine, peach, hops and turf uses. The chronic LOC on a dose 

basis is exceeded for all uses and the chronic LOC on a dietary 

basis is exceeded for apples, apricots, cherries, nectarines, 

peaches, cotton and turf. For granular uses, the acute listed 

species LOC is exceeded for turf. For terrestrial invertebrates, 

the acute contact LD50 is greater than the highest dose tested. In 

addition, there were no mortalities. Risk the terrestrial 

invertebrates will be discussed qualitatively in the risk 

description. For terrestrial-phase amphibians, birds are used as a 

surrogate. For birds, There are dose-based acute LOC 

exceedances (RQ > 0.1) for all uses except 

Boysenberry/Dewberry/Youngberry. The chronic avian LOC is 

102
LOC 

Assessment Endpoint Exceedances Description of Results of Risk Estimation 

(Y/N) 

exceeded for turf and cotton uses. 

Indirect Effects 

Survival, growth, and reproduction 

of CRLF individuals via effects on 

habitat (i.e., riparian vegetation) 

Unknown No vegetative vigor or seedling emergence plant toxicity data 

are available. A qualitative discussion of risk is provided. 

Table 5.9 Risk Estimation Summary for Myclobutanil – PCEs of Designated 

Critical Habitat for the CRLF 

Assessment Endpoint Habitat Effects 

(Y/N) Description of Results of Risk Estimation 

Aquatic Phase PCEs 

(Aquatic Breeding Habitat and Aquatic Non-Breeding Habitat)

Alteration of channel/pond morphology or 

geometry and/or increase in sediment 

deposition within the stream channel or 

pond: aquatic habitat (including riparian 

vegetation) provides for shelter, foraging, 

predator avoidance, and aquatic dispersal 

for juvenile and adult CRLFs. 

Unknown There are no LOC exceedences for aquatic nonvascular plants. No aquatic vascular or terrestrial 

plant data are available. A qualitative discussion of 

risk is provided. 

Alteration in water chemistry/quality 

including temperature, turbidity, and oxygen 

content necessary for normal growth and 

viability of juvenile and adult CRLFs and 

their food source. 

Unknown There are no LOC exceedences for aquatic nonvascular plants. No aquatic vascular or terrestrial 

plant data are available. A qualitative discussion of 

risk is provided. 

Alteration of other chemical characteristics 

necessary for normal growth and viability of 

CRLFs and their food source. 

Unknown There are no LOC exceedences for listed species 

following acute and chronic exposure to freshwater 

fish or acute exposure to freshwater invertebrates. 

There are no LOC exceedences for aquatic nonvascular plants. No data are available for freshwater 

invertebrates (chronic exposure) or aquatic vascular 

plants. A qualitative discussion of risk is provided. 

Reduction and/or modification of aquaticbased food sources for pre-metamorphs 

(e.g., algae) 

N There are no LOC exceedences for aquatic nonvascular plants. 

Terrestrial Phase PCEs 

(Upland Habitat and Dispersal Habitat)

Elimination and/or disturbance of upland 

habitat; ability of habitat to support food 

source of CRLFs: Upland areas within 200 

ft of the edge of the riparian vegetation or 

dripline surrounding aquatic and riparian 

habitat that are comprised of grasslands, 

woodlands, and/or wetland/riparian plant 

species that provides the CRLF shelter, 

forage, and predator avoidance 

Unknown No vegetative vigor or seedling emergence plant 

toxicity data are available. A qualitative discussion 

of risk is provided. 

Elimination and/or disturbance of dispersal 

habitat: Upland or riparian dispersal habitat 

Unknown No vegetative vigor or seedling emergence plant 

toxicity data are available. A qualitative discussion 

103
Habitat Effects Assessment Endpoint Description of Results of Risk Estimation (Y/N) 

within designated units and between 

occupied locations within 0.7 mi of each 

other that allow for movement between sites 

including both natural and altered sites 

which do not contain barriers to dispersal 

of risk is provided. 

Reduction and/or modification of food 

sources for terrestrial phase juveniles and 

adults 

Y For mammals, the acute and chronic LOCs are 

exceeded for multiple crops. For terrestrial 

invertebrates, the acute contact LD50 is greater than 

the highest dose tested with no mortalities. Risk the 

terrestrial invertebrates will be discussed 

qualitatively in the risk description. For terrestrialphase amphibians, birds are used as a surrogate. 

Acute and chronic LOCs are exceeded for multiple 

crops. 

Alteration of chemical characteristics 

necessary for normal growth and viability of 

juvenile and adult CRLFs and their food 

source. 

Y See above box. 

Following a “may affect” determination, additional information is considered to refine 

the potential for exposure at the predicted levels based on the life history characteristics 

(i.e., habitat range, feeding preferences, etc.) of the CRLF. Based on the best available 

information, the Agency uses the refined evaluation to distinguish those actions that 

“may affect, but are not likely to adversely affect” from those actions that are “likely to 

adversely affect” the CRLF and its designated critical habitat. 

The criteria used to make determinations that the effects of an action are “not likely to 

adversely affect” the CRLF and its designated critical habitat include the following: 

• Significance of Effect: Insignificant effects are those that cannot be meaningfully 

measured, detected, or evaluated in the context of a level of effect where “take” 

occurs for even a single individual. “Take” in this context means to harass or 

harm, defined as the following: 

 Harm includes significant habitat effects or degradation that results in 

death or injury to listed species by significantly impairing behavioral 

patterns such as breeding, feeding, or sheltering. 

 Harass is defined as actions that create the likelihood of injury to listed 

species to such an extent as to significantly disrupt normal behavior 

patterns which include, but are not limited to, breeding, feeding, or 

sheltering. 

• Likelihood of the Effect Occurring: Discountable effects are those that are 

extremely unlikely to occur. 

• Adverse Nature of Effect: Effects that are wholly beneficial without any adverse 

effects are not considered adverse. 

 

104
A description of the risk and effects determination for each of the established assessment 

endpoints for the CRLF and its designated critical habitat is provided in Sections 5.2.1 

through 5.2.3 

5.2.1 Direct Effects 

5.2.1.1 Aquatic-Phase CRLF 

The aquatic-phase considers life stages of the frog that are obligatory aquatic organisms, 

including eggs and larvae. It also considers submerged terrestrial-phase juveniles and 

adults, which spend a portion of their time in water bodies that may receive runoff and 

spray drift containing myclobutanil. 

Acute and chronic RQs for all modeled scenarios for myclobutanil and myclobutanil plus 

1,2,4 triazole were lower than the related LOC. The highest acute RQ was 0.025 and the 

highest chronic RQ was 0.061, both RQs based on the turf scenario. The probability of 

an individual effect at the highest RQ (turf scenario) is estimated to be 1 in 3.56 x 1012 (1 

in 1.48 x 103 to 1 in 5.06 x 1046, 95% C.I.) based on a default slope assumption of 4.5 (2 

to 9, 95% C.I.) 

Water monitoring and rainfall data support the risk conclusions based on RQs calculated 

with modeled EECs. The available non-targeted monitoring data show myclobutanil 

concentrations that are much lower than the modeled concentrations. The highest 

concentrations of myclobutanil were detected in surface water. Myclobutanil was 

detected in ambient surface water (Table 3.3) at a detection frequency of 37.8 % (166 of 

439 samples) collected in five counties in California. The maximum daily myclobutanil 

concentration was 0.507 μg/L for a sampling site (USGS Sampling Station 

373112120382901) located near Montpelier California in Merced County California. In 

comparison to surface water monitoring data which did not include 1,2,4-triazole, the 

lowest modeled concentrations of myclobutanil (plus 1,2,4 triazole) were 2.84 μg/L 

(peak), 2.82 μg/L (21-day), and 2.77 μg/L (60-day). 

There are no relevant data in the open literature and no incident data for fish. 

The effects determination is no effect on aquatic-phase CRLF from direct exposures to 

myclobutanil. 

5.2.1.2 Terrestrial-Phase CRLF 

As stated in the Risk Estimation section (Section 5.1.2.1), the acute avian dose-based 

RQs exceed the acute LOC for listed species (0.1) for all uses of myclobutanil except 

boysenberry/dewberry/youngberry at an application rate of 0.0625 lbs. a.i./A. In an effort 

to refine the acute dose-based risk estimates, the T-REX model was modified to account 

for the lower metabolic rate and lower caloric requirement of amphibians (compared to 

birds). Acute dose-based RQs were recalculated using the T-HERPS (Version 1.0) model 

105
for small (1 g), medium (37 g), and large (238 g) frogs. An example output from THERPS is in Appendix M. Using this refinement, the acute dose-based RQ exceeds the 

acute listed species LOC of 0.1 for 238 gram amphibians eating small herbivorous 

mammals following application to turf. The dose-based RQs for 37 gram amphibians 

eating small herbivorous mammals exceed the acute LOC for listed species following 

application to all crops except boysenberry/dewberry/youngberry at an application rate of 

0.0625 lbs a.i./A and tomatoes at 0.1 lbs a.i./A (see Table 5.10). 

Table 5.10 Thirty Seven Gram Amphibian T-HERPS RQs for Consumption of 

Small Herbivorous Mammals 

USE RQ 

Almond 0.16 

Apple 0.49 

Apricot 0.28 

Artichoke 0.10 

Asparagus 0.13 

Beans 0.12 

Blackberry/EggPlant/Okra/Pepper/Raspberry 0.11 

Boysenberry/Dewberry/Youngberry 0.06 

Carrot 0.10 

Canistel/Mango/Papaya/Sapodilla 0.28 

Cherry/Nectarine/Peach 0.39 

Cucurbit Vegetables 0.14 

Currant 0.13 

Gooseberry 0.17 

Grapes 0.13 

Hops 0.25 

Lettuce 0.10 

Plum/Prune 0.23 

Tomato 0.07 

Turf 1.41 

1

 Bold indicates that the RQ exceeds the listed species LOC of 0.1 2

 T-HERPS turf use RQ for 238 gram amphibians consuming small herbivorous mammals = 0.22, which 

exceeds the acute listed species LOC of 0.1 

In the acute oral study with Bobwhite quail (MRID 00144286), lethargy and anorexia 

were observed in all birds at all dose levels. The lowest dose level tested was 316 mg/kg 

bw. These symptoms lasted until death in the two highest test doses (1000 and 1470 

mg/kg bw), seven days at 681 mg/kg bw, three days at 464 mg/kg bw, and two days at 

the lowest dose. All birds except for one each in the 1000 and 681 mg/kg bw groups 

showed distention of the crop containing either test material or air, and food. Five birds 

(two from the 464 mg/kg group and one each from the 681, 1000 and 1470 mg/kg 

groups) showed microscopic findings in liver and intestinal tissues. Three of the 

surviving birds showed microscopic findings in liver and intestinal tissues. Since all 

birds were affected in this study, no NOAEL could be established. The lowest dose 

tested (316 mg/kg bw) corresponds to an adjusted dose of 228 mg/kg bw for a 20 gram 

bird. For the turf use, the dose-based EEC for small insects is 693 mg/kg bw, which is 

106
higher than the lowest dose tested adjusted for a 20 gram bird. The dose-based EEC for 

small insects is also greater than the lowest adjusted dose tested. None of the other uses 

generated dose-based EECs for small insects that were greater than the lowest adjusted 

dose tested. The dose-based EECs ranged from 29 for 

Boysenberry/Dewberry/Youngberry to 693 for turf (see Table 3.9 in Section 3.3). Since 

there were effects at the lowest dose, there is an uncertainty associated with potential 

sublethal effects in birds on a dose-basis for all the uses. 

 

The probability of an individual effect on a dose-basis ranges from 1 in ~ 1.54E+14 for 

uses on boysenberry/dewberry/youngberry to 1 in ~ 1 for use on turf. The highest 

probabilities are for uses on turf, apples (1 in ~ 7.24E+00), cherries/nectarines/peaches (1 

in ~ 2.61E+01), canistel/mango/papaya/sapodilla (1 in ~ 4.95E+02) and apricots (1 in ~ 

3.88E+02). 

RQs on an acute dietary basis were not estimated because the LC50 value exceeds the 

maximum limit concentration tested. As stated in the effects section, myclobutanil is 

categorized as slightly toxic on a dietary basis with subacute dietary LC50’s of >4090 ppm 

for mallard ducks (MRID 00144288) and > 4530 ppm for bobwhite quail (MRID 

00144287). Although no definitive subacute dietary LC50’s could be determined from 

these studies, there were mortalities in both studies. There was one mortality at 4090 

ppm, the highest concentration tested in mallard ducks and mortalities at 3000 ppm and 

4530 ppm, the highest concentrations tested in bobwhite quail. The estimated dietarybased EEC for small insects following use on turf is 609 ppm, which is roughly 4.9 times 

lower than 3000 ppm, the lowest concentration where mortality was observed (e.g., the 

upper bound subacute dietary based RQ would be 0.2). This value is greater than the 

avian acute risk to listed species LOC of 0.1. Therefore, there is an uncertainty 

associated with potential mortality to listed species following turf uses. For apples, 

which have the next highest terrestrial exposure on a dietary basis the EEC is 222 ppm 

for small insects, which is 13.5 times less than the lowest concentration where mortality 

was observed (e.g., the upper bound subacute dietary based RQ would be 0.07). This is 

less than the acute avian LOC for listed species. 

As stated in the Risk Estimation section, the chronic avian LOC is exceeded following 

use on turf and cotton (assuming 100% of seed available). None of the other uses 

generated chronic RQs that exceeded the chronic LOC. 

There were no avian or amphibian studies available in the ECOTOX open literature for 

myclobutanil. Similarly, no myclobutanil incidents have been reported involving birds or 

terrestrial-phase amphibians. 

 The Agency concludes that there is a potential direct impact to the terrestrial-phase 

CRLF. The effects determination is likely to adversely affect based on the weight of the 

evidence as follows: 

107
• Acute dose-based RQs estimated from T-HERPS exceed the acute LOC of 0.1 for 

listed species for both 37 and 238 gram amphibians eating small herbivorous 

mammals following application to turf. The dose-based RQs for 37 gram 

amphibians eating small herbivorous mammals exceed the acute LOC for listed 

species following application to all crops except 

boysenberry/dewberry/youngberry and tomatoes. 

• On an acute dose-basis, there is an uncertainty associated with potential sublethal 

effects for all uses. 

• Based on the lowest dietary concentration where mortality was observed in the 

subacute dietary studies (both studies had LC50’s greater than the highest 

concentration tested), there is an uncertainty associated with potential mortality to 

listed species following turf uses. 

• The highest probabilities of an individual effect on a dose-basis are for uses on 

turf (1 in ~ 1), apples (1 in ~ 7.24E+00), cherries/nectarines/peaches (1 in ~ 

2.61E+01), canistel/mango/papaya/sapodilla (1 in ~ 4.95E+02) and apricots (1 in 

~ 3.88E+02). 

• The chronic avian LOC is exceeded following use on turf and cotton (assuming 

100% of seed available). 

5.2.2 Indirect Effects (via Reductions in Prey Base) 

5.2.2.1 Algae (non-vascular plants) 

As discussed in Section 2.5.3, the diet of CRLF tadpoles is composed primarily of 

unicellular aquatic plants (i.e., algae and diatoms) and detritus. Acute RQs for aquatic 

non-vascular plants did not exceed the LOC of 1 for any of the assessed uses. The 

highest acute RQ (0.074) was for the turf scenario. As previously discussed, available 

monitoring data show myclobutanil concentrations that are much lower than the modeled 

concentrations. There are no relevant data in the open literature and no incident data for 

aquatic plants. The effects determination is no effect on indirect impact to the CRLF via 

effects of myclobutanil on algal food items. 

5.2.2.2 Aquatic Invertebrates 

The potential for myclobutanil to elicit indirect effects to the CRLF via effects on 

freshwater invertebrate food items is dependent on several factors including: (1) the 

potential magnitude of effect on freshwater invertebrate individuals and populations; and 

(2) the number of prey species potentially affected relative to the expected number of 

species needed to maintain the dietary needs of the CRLF. Together, these data provide a 

basis to evaluate whether the number of individuals within a prey species is likely to be 

reduced such that it may indirectly affect the CRLF. 

No acute RQs exceeded the endangered species LOC of 0.05. The highest acute RQ for 

aquatic invertebrates was 0.005 (turf scenario). At this RQ, the percent effect to the 

108
aquatic invertebrate prey base is < 0.001% (i.e. the percentage of the aquatic invertebrate 

population that may be affected following exposure to myclobutanil). 

No chronic freshwater invertebrate toxicity data are available for myclobutanil. It was 

not possible to estimate a chronic toxicity value for freshwater invertebrates using an 

acute to chronic ratio with estuarine/marine invertebrate data because no chronic studies 

are available for myclobutanil. Therefore, a quantitative assessment of risk following 

chronic exposure to myclobutanil was not possible using these methods. However, the 

risk may be considered using other approaches. 

Using the modeled EECs, freshwater invertebrate chronic toxicity values that would 

trigger an exceedence of the LOC can be calculated for myclobutanil. The highest 21-

day EEC modeled is 61.15 ug/L (turf scenario). Based on that value, for myclobutanil a 

chronic toxicity value of ≤ 0.061 mg/L would exceed the LOC of 1. In the context of the 

acute toxicity of myclobutanil to aquatic invertebrates (11 mg/L), a chronic toxicity value 

≤ 0.061 mg/L would yield an acute to chronic ratio of ≥180. 

As previously described, acute and chronic toxicity data from other conazole (DMI 

triazole) fungicides were available for aquatic invertebrates. For risk description 

purposes, these endpoints were used to calculate acute to chronic ratios, assuming that 

myclobutanil toxicity is similar to other conazoles due to similar mode of action. Data 

were available for nine conazole to calculate acute to chronic ratios from water flea 

(Daphnia magna) studies (the species which acute data is available for myclobutanil). 

As applied to myclobutanil, only one of the conazole acute-to-chronic ratios (high-end 

estimate for cyproconazole = 1368) is higher that the ratio of ≥180 that would trigger 

chronic LOC exceedences for freshwater invertebrates based on myclobutanil modeled 

EECs. Assuming an acute-to-chronic ratio of 1368, chronic toxicity of myclobutanil to 

freshwater invertebrates is estimated to be 8.04 μg/L. Based on this high-end estimate 

for cyproconazole, RQs based on the 21-day EEC of myclobutanil plus 1,2,4 triazole 

range from 0.35 to 7.61. Nearly all uses exceed the chronic LOC of 1; only those with 

21-day EECs less than 8.04 μg/L do not exceed (see Table 3.6). It is important to note 

that there were two available chronic toxicity studies for cyproconazole. The 

NOAEC/LOAECs for these two studies are: 0.019/0.073 and 0.29/0.57 mg/L, 

respectively. Both studies are acceptable for assessment of risk, but the one with the 

lower endpoints was graded as supplemental and was a static study. The other study with 

the higher endpoints was graded acceptable and was a flow-through study. The low end 

cyproconazole acute-to-chronic ratio estimate (89.6) is less than the ratio of ≥180 that 

would trigger LOC exceedences for myclobutanil. Thus, as applied to myclobutanil there 

are no exceedences of the LOC based on the lower end acute-to-chronic estimate for 

cyproconazole. Cyproconazole toxicity data suggests the possibility of effects from 

myclobutanil on freshwater invertebrates that may exceed the LOC. However, there is 

considerable uncertainty associated with extrapolating toxicity from other conazoles to 

myclobutanil including the high variability among conazole acute-to-chronic ratios 

(range from 2.4 to 1368). Thus, the effects of myclobutanil cannot be quantified without 

data on myclobutanil toxicity to aquatic invertebrates. 

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In addition to studies on the water flea (Daphnia magna), four of the conazoles had 

studies submitted for other aquatic invertebrate taxa. For these four conazoles, Daphnia 

magna was the most sensitive aquatic invertebrate species tested. 

As previously discussed, available monitoring data show myclobutanil concentrations 

that are much lower than the modeled concentrations. It was observed that the Tier II 

EECs indicated year-to-year accumulation of myclobutanil in the standard pond model. 

However, this accumulation is not unexpected due to the persistence of myclobutanil and 

myclobutanil plus 1,2,4-triazole in soil and water environments, and the lack of inflow 

and outflow in the standard pond model that precludes decreases in concentrations of 

residues due to dilution. Therefore, the accumulation is conservative (an overestimate) 

compared to flowing systems. Furthermore, the Koc is probably not high enough for 

accumulation in the sediment to be much of an issue. 

There are no acceptable open literature data available or reported aquatic invertebrate 

incidents attributed myclobutanil. 

Based on the weight of evidence, there is minimal potential indirect impact to the CRLF 

via effects of myclobutanil on freshwater invertebrate food items. The effects 

determination is no effect on an acute basis and may effect, not likely to adversely affect 

on a chronic basis. 

5.2.2.3 Fish and Aquatic-phase Frogs 

Myclobutanil is moderately toxic on an acute basis to freshwater fish, the surrogate for 

the aquatic-phase CRLF. The acute and chronic RQs for all modeled scenarios for 

myclobutanil and myclobutanil plus 1,2,4 triazole were lower than the related LOC. The 

probability of an individual effect at the highest RQ (turf scenario) is estimated to be 1 in 

3.56 x 1012 (1 in 1.48 x 103

 to 1 in 5.06 x 1046, 95% C.I.) based on a default slope 

assumption of 4.5 (2 to 9, 95% C.I.). Water monitoring and rainfall data support the risk 

conclusions based on RQs calculated with modeled EECs. Available monitoring data 

show myclobutanil concentrations that are much lower than the modeled concentrations. 

There are no relevant data in the open literature and no incident data for fish. The effects 

determination is myclobutanil has “no effect” on indirectly impacting the aquatic-phase 

CRLF based on the endpoints generated from the freshwater fish data. 

5.2.2.4 Terrestrial Invertebrates 

When the terrestrial-phase CRLF reaches juvenile and adult stages, its diet is mainly 

composed of terrestrial invertebrates. As stated in the risk estimation section (Section 

5.1.2), the acute RQs for terrestrial invertebrates were not estimated because no definitive 

LC50 can be estimated from the available data. The data indicate no mortalities at 

concentration levels up to and including 2836 μg a.i./g bw or 2836 ppm (highest level 

110
tested) in the acute contact study with honey bees. The estimated dietary-based EEC for 

small insects with the use on turf is 608.82 ppm, which is 4.7 times lower than 2836 ppm 

(e.g., the upper bound acute RQ would be 0.21). This value is higher than the acute LOC 

of 0.05 for listed terrestrial invertebrate species. Upper bound RQs for small insects 

would also slightly exceed the acute LOC for apple (RQ = 0.08) and cherry, nectarine 

and peach uses (RQ = 0.06). Estimated upper bound small insect RQs for all other uses 

are below the LOC. Based on the above estimates for small insects, there is an 

uncertainty associated with potential mortality for listed terrestrial invertebrates. The 

estimated dietary-based EEC for large insects with the use on turf is 67.65 ppm. This is 

41 times lower than 2836 ppm (upper bound RQ of 0.02). This value is lower than the 

acute LOC of 0.05 for listed terrestrial invertebrate species and thus, there is no concern 

for listed large invertebrates for any of the myclobutanil uses. 

As noted in Section 4.2 on toxicity to terrestrial organisms, one of the five available 

literature studies on terrestrial invertebrates provided an LD50. Three mite studies and 

one arthropod study showed no adverse effects on the species evaluated. A single study 

on mirids provided an LD50 of 150 μg ai/L to adult mirids. The study did not show 

toxicity to nymphs. A quantitative analysis of potential risk to terrestrial invertebrates 

based on the LD50 for mirids cannot be conducted, however, because insufficient data are 

available to calculate ppm exposures (i.e., data on the weight of the organism are not 

available). However, based on the results of the honey bee study, the absence of adverse 

effects in four of the five available literature studies, and the fact that the mirid study 

showed no toxicity to nymphs, minimal potential indirect impact to the CRLF via effects 

of myclobutanil on freshwater invertebrate food items is expected. The effects 

determination is may affect, not likely to adversely affect. 

5.2.2.5 Mammals 

Life history data for terrestrial-phase CRLFs indicate that large adult frogs consume 

terrestrial vertebrates, including mice. The dose-based chronic RQs exceed the listed 

species chronic LOC for all uses and the dietary-based chronic RQs for a number of 

myclobutanil uses. The dose-based acute RQs also exceed the listed species acute RQs 

for a number of uses. The chronic dietary-based RQ exceedances range from 1.1 for uses 

of myclobutanil on canistel, mango, papaya and sapodilla to 5.4 for uses on turf. Chronic 

dose-based RQs range from 1.24 (caneberries) to 29.35 (turf). Acute dose-based RQ 

exceedances range from 0.12 (plums and hops) to 0.68 (turf). At the lowest acute RQ 

exceedance of 0.12 for hops and plums, the expected effect on the prey population is 

13.7% based on a default slope factor of 1.19. The highest acute RQ exceedance for turf 

of 0.68 corresponds with an expected effect on the prey population of 42%. As noted in 

Section 4.2, the 60 DF myclobutanil formulation was identified as potentially more toxic 

than the technical material based on a rat LD50 of 980 mg formulation/kg bw for the 60 

DF product. The 60 DF formulation is used only on apple and grape crops. Therefore, 

RQs were derived using the rat LD50 for the 60 DF formulation for apples (RQ = 0.21) 

and grapes (RQ = 0.05). These results indicate that based on actual use parameters, the 

60 DF formulation does not present higher toxicity in the field than other formulations 

111
when applied at label prescribed rates. Based on the weight-of-evidence, uses for 

myclobutanil may indirectly impact the CRLF through effects to the mammalian prey 

base. The effects determination is likely to adversely affect. 

5.2.2.6 Terrestrial-phase Amphibians 

Terrestrial-phase adult CRLFs also consume frogs. RQ values representing direct 

exposures of myclobutanil to terrestrial-phase CRLFs are used to represent exposures of 

myclobutanil to frogs in terrestrial habitats. Based on the assessment of risk to the 

terrestrial-phase CRLF (direct effects), the Agency concludes that myclobutanil may 

indirectly impact the CRLF through effects to the terrestrial-phase amphibian prey base. 

The effects determination is likely to adversely affect (see Section 5.2.1.2 for more 

details). 

5.2.3 Indirect Effects (via Habitat Effects) 

5.2.3.1 Aquatic Plants (Vascular and Non-vascular) 

Aquatic plants serve several important functions in aquatic ecosystems. Non-vascular 

aquatic plants are primary producers and provide the autochthonous energy base for 

aquatic ecosystems. Vascular plants provide structure as attachment sites and refugia for 

many aquatic invertebrates, fish, and juvenile organisms, such as fish and frogs. In 

addition, vascular plants also provide primary productivity and oxygen to the aquatic 

ecosystem. Rooted plants help reduce sediment loading and provide stability to 

nearshore areas and lower streambanks. In addition, vascular aquatic plants are important 

as attachment sites for egg masses of CRLFs. 

Potential indirect effects to the CRLF based on impacts to habitat and/or primary 

production were assessed using RQs for aquatic freshwater non-vascular plants based on 

myclobutanil toxicity data. There is no freshwater vascular plant data for myclobutanil 

so risk is assessed qualitatively. 

As previously discussed, acute RQs for aquatic non-vascular plants did not exceed the 

LOC of 1 for any of the assessed uses. 

No aquatic vascular plant toxicity data are available for myclobutanil. As previously 

described, toxicity data from other conazoles were used to assess risk from myclobutanil. 

For the seven conazole fungicides evaluated, the range of 7/14-day EC50s was 0.02 to 

9.02 mg a.i./L and the mean was 1.84 mg a.i./L. Assuming that myclobutanil toxicity to 

aquatic vascular plants is similar to other conazoles, there were no exceedences of the 

LOC using the EC50 data from 6 of the 7 conazoles and the conazole mean EC50. 

However, using the most sensitive endpoint (metconazole = 0.02 mg a.i./L), resulted in 

exceedences of the LOC of 1 for about one third of the myclobutanil use scenarios (RQs 

based on myclobutanil plus 1,2,4 triazole EECs ranged from 0.13 to 2.79). Metaconazole 

112
toxicity data suggests the possibility of effects from myclobutanil on aquatic vascular 

plants that may exceed the LOC. However, there is considerable uncertainty associated 

with extrapolating toxicity from other conazoles to myclobutanil, thus the effects of 

myclobutanil cannot be quantified without data on myclobutanil toxicity to aquatic 

vascular plants. 

As previously discussed, available monitoring data show myclobutanil concentrations 

that are much lower than the modeled concentrations. There are no acceptable open 

literature data available or reported aquatic plant incidents attributed myclobutanil. 

Based on the weight of evidence, there is minimal potential indirect impact to the CRLF 

(habitat effects) based on effects of myclobutanil on aquatic plants (vascular and nonvascular). The effects determination is may effect, not likely to adversely affect. 

5.2.3.2 Terrestrial Plants 

There are no registrant-submitted terrestrial plant toxicity data for myclobutanil for 

assessment of the potential for indirect effects to the aquatic- and terrestrial-phase CRLF 

via effects to riparian vegetation or effects to the primary constituent elements (PCEs) 

relevant to the aquatic- and terrestrial-phase CRLF. As stated previously, limited 

evidence in the open literature indicates that myclobutanil has the potential to elicit 

phototoxic effects. At 1.07 lbs a.i./A applied at 28-30 day intervals, there was evidence 

of decreased quality of “Tifgreen” Bermuda grass (ECOTOX ref. no. 76524). One 

incident report (I014702-074) indicated foliar necrosis and some defoliation with roses 

after exposure to myclobutanil. Damage varied from house to house and by rose variety. 

The certainty index for this incident (I014702-074) was possible. The application rate(s) 

were not reported for this incident. 

Also stated previously, myclobutanil is a member of the class of triazole sterol 14αdemethylase-inhibitors (DMIs). To date, no other DMI triazole fungicides have been 

assessed for risk to the CRLF. However, terrestrial plant studies are available on 5 other 

DMI triazole fungicides that have at least one endpoint that may be used in the TerrPlant 

(v. 1.2.2) model for terrestrial plants. For risk description purposes, these endpoints were 

used in the model as surrogates for myclobutanil, using the solubility of myclobutanil for 

the potential runoff fraction. In general, using the endpoints from the other triazole DMI 

fungicides with the myclobutanil application rates, dicots living in semi-aquatic areas 

would be the most sensitive terrestrial plant species. The TerrPlant model was used to 

determine the myclobutanil application rates that would exceed the LOC for listed dicots 

and non-listed dicots inhabiting semi-aquatic areas for both aerial and ground 

applications. Table 5.11 summarizes these application rates. 

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Table 5.11 Myclobutanil Application Rates Combined with Endpoints from 5 

Triazole DMI Fungicides Exceeding the Terrestrial Plant LOC for Listed and NonListed Dicots in Semi-Aquatic Areas 

Application Rate (lbs a.i./A) 

Triazole Fungicide Non-listed dicots Listed dicots 

Aerial, Airblast, 

Spray 

Chemigation 

Ground Aerial, Airblast, 

Spray 

Chemigation 

Ground 

Cyproconazole 0.16 0.17 0.12 0.13 

Metconazole 0.28 0.30 0.14 0.15 

Propiconazole 0.33 0.36 0.10 0.11 

Prothioconazole Not available1 Not available1 0.05 0.06 

Triticonazole 0.03 0.03 0.007 0.008 1

 No EC25 available 

It is noted that the labeled uses of myclobutanil include direct application to a variety of 

terrestrial plants (agricultural and ornamental) at multiple growth stages (e.g., seed 

treatment, pre-bloom, bloom, foliar, post-bloom etc.). Considering the fact that the labels 

provide for exposure to terrestrial plants throughout the growth stage, it is probable that 

the damage to the crops is not so extensive to inhibit the use of this pesticide by 

applicators. 

Nevertheless, due to the lack of terrestrial plant data and weight of the evidence from 

information provided in the open literature, incident data and the fact that surrogate data 

from similar fungicides would exceed the terrestrial plant LOC for many of the 

myclobutanil uses, it is determined that there is a potential of indirect impacts to the 

CRLF (habitat effects) based on effects of myclobutanil on terrestrial plants. The effects 

determination is likely to adversely affect. 

5.2.4 Effects to Designated Critical Habitat 

Risk conclusions for the designated critical habitat are the same as those for indirect 

effects. 

5.2.4.1 Aquatic-Phase PCEs 

Three of the four assessment endpoints for the aquatic-phase primary constituent 

elements (PCEs) of designated critical habitat for the CRLF are related to potential 

effects to aquatic and/or terrestrial plants: 

• Alteration of channel/pond morphology or geometry and/or increase in sediment 

deposition within the stream channel or pond: aquatic habitat (including riparian 

vegetation) provides for shelter, foraging, predator avoidance, and aquatic 

dispersal for juvenile and adult CRLFs. 

114
• Alteration in water chemistry/quality including temperature, turbidity, and 

oxygen content necessary for normal growth and viability of juvenile and adult 

CRLFs and their food source. 

• Reduction and/or modification of aquatic-based food sources for pre-metamorphs 

(e.g., algae). 

Conclusions for potential indirect effects to the CRLF via direct effects to aquatic and 

terrestrial plants are used to determine whether effects to critical habitat may occur. There 

were no LOC exceedences for aquatic non-vascular plants (section 5.2.2.1). As stated 

previously, toxicity data from other conazole (triazole) fungicides were used to 

characterize risk to aquatic vascular plants, assuming that myclobutanil toxicity is similar 

to other conazoles due to similar mode of action (section 5.2.3.1). There were no 

exceedences of the LOC using the EC50 data from 6 of the 7 conazoles and the conazole 

mean EC50. However, using the most sensitive endpoint resulted in exceedences of the 

LOC for about one third of the myclobutanil use scenarios. There are no registrantsubmitted terrestrial plant toxicity data for myclobutanil. When the results of terrestrial 

plant studies conducted with five other triazole DMI fungicides are used with the 

application rates for myclobutanil in the Terrplant model, dicots living in semi-aquatic 

areas appear to be the most sensitive terrestrial plants, with potential exceedance of the 

terrestrial plant LOC for a variety of uses (section 5.2.3.2). Overall, there is a potential 

for effects to habitat via impacts to terrestrial plants. 

The remaining aquatic-phase PCE is “alteration of other chemical characteristics 

necessary for normal growth and viability of CRLFs and their food source.” This PCE is 

assessed by considering impacts to algae as food items for tadpoles and direct and 

indirect effects to the aquatic-phase CRLF via acute and chronic freshwater fish and 

invertebrate toxicity endpoints as measures of effects. There were no LOC exceedences 

for aquatic non-vascular plants, freshwater fish, or freshwater invertebrates (acute 

effects). No chronic freshwater invertebrate studies are available for myclobutanil. 

There are no exceedences of the freshwater invertebrate chronic LOC using toxicity data 

from 8 of 9 conazoles with similar mechanisms of toxicity. For the 9th conazole, 2 

chronic toxicity studies are available, one of which indicates LOC exceedances and the 

other does not. Overall, effects to habitat are not expected via alteration of other 

chemical characteristics necessary for normal growth and viability of CRLFs and their 

food source. 

5.2.4.2 Terrestrial-Phase PCEs 

Two of the four assessment endpoints for the terrestrial-phase PCEs of designated critical 

habitat for the CRLF are related to potential effects to terrestrial plants: 

• Elimination and/or disturbance of upland habitat; ability of habitat to support food 

source of CRLFs: Upland areas within 200 ft of the edge of the riparian 

vegetation or drip line surrounding aquatic and riparian habitat that are comprised 

of grasslands, woodlands, and/or wetland/riparian plant species that provides the 

CRLF shelter, forage, and predator avoidance. 

115
• Elimination and/or disturbance of dispersal habitat: Upland or riparian dispersal 

habitat within designated units and between occupied locations within 0.7 mi of 

each other that allow for movement between sites including both natural and 

altered sites which do not contain barriers to dispersal. 

There are no registrant-submitted terrestrial plant toxicity data for myclobutanil for 

assessment of effects to the primary constituent elements (PCEs) relevant to the aquaticand terrestrial-phase CRLF. As stated above, there is limited evidence in the open 

literature that myclobutanil has the potential to elicit phototoxic effects and one incident 

was reported in which myclobutanil may have caused some foliar necrosis and 

defoliation in roses. In addition, when the results of terrestrial plant studies conducted 

with five other triazole DMI fungicides are used with the application rates for 

myclobutanil in the TerrPlant model, dicots living in semi-aquatic areas appear to be the 

most sensitive terrestrial plants, with potential exceedance of the terrestrial plant LOC for 

a variety of uses. Therefore, there is a potential for effects to habitat via effects to 

terrestrial plants (Section 5.2.3.2). 

The third terrestrial-phase PCE is “reduction and/or modification of food sources for 

terrestrial phase juveniles and adults.” To assess the impact of myclobutanil on this PCE, 

acute and chronic toxicity endpoints for terrestrial invertebrates, mammals, and 

terrestrial-phase frogs are used as measures of effects. For terrestrial invertebrates, 

although there is an uncertainty associated with potential mortality for listed small 

terrestrial invertebrates following acute exposure, based on the lack of mortality in the 

honey bee study, the absence of adverse effects in four of the five available literature 

studies, and the fact that the mirid study showed no toxicity to nymphs, it was determined 

that although there may be an effect, it is not likely to adversely affect the terrestrial 

invertebrate prey base for the CRLF. For mammals, the acute listed species LOC and the 

chronic LOC are exceeded for multiple uses. For terrestrial-phase amphibians, using 

birds as a surrogate, there are acute LOC listed species exceedances for multiple uses. 

The chronic avian LOC is exceeded for turf and cotton uses. Therefore, there is a 

potential for effects to habitat via indirect effects to terrestrial-phase CRLFs via reduction 

in prey base (Sections 5.2.2.5 for mammals, and 5.2.2.6 for frogs). 

The fourth terrestrial-phase PCE is based on alteration of chemical characteristics 

necessary for normal growth and viability of juvenile and adult CRLFs and their food 

source. Again, for terrestrial invertebrates, although there is an uncertainty associated 

with potential mortality for listed small terrestrial invertebrates following acute exposure, 

based on the lack of mortality in the honey bee study, the absence of adverse effects in 

four of the five available literature studies, and the fact that the mirid study showed no 

toxicity to nymphs, it was determined that although there may be an effect, it is not likely 

to adversely affect the terrestrial invertebrate prey base for the CRLF. For mammals, the 

acute listed species LOC and the chronic LOC are exceeded for multiple uses. For 

terrestrial-phase amphibians, using birds as a surrogate, there are acute LOC listed 

species exceedances for multiple uses. The chronic avian LOC is exceeded for turf and 

116
cotton uses. Therefore, there is a potential for effects to habitat via indirect effects 

(Sections 5.2.2.5 for mammals and 5.2.2.6 for frogs) to terrestrial-phase CRLFs. 

5.2.5 Spatial Extent of Potential Effects 

An LAA effects determination applies to those areas where it is expected that the 

pesticide’s use will directly or indirectly affect the CRLF or its designated critical habitat. 

To determine this area, the footprint of myclobutanil’s use pattern is identified, using 

land cover data that correspond to myclobutanil’s use pattern. The spatial extent of the 

effects determination also includes areas beyond the initial area of concern that may be 

impacted by runoff and/or spray drift. The identified direct/indirect effects and/or effects 

to critical habitat are anticipated to occur only for those currently occupied core habitat 

areas, CNDDB occurrence sections, and designated critical habitat for the CRLF that 

overlap with the initial area of concern plus greater than 158 feet from its boundary. It is 

assumed that non-flowing waterbodies (or potential CRLF habitat) are included within 

this area. 

In addition to the spray drift buffer, a downstream dilution extent analysis would 

normally be conducted that would result in a specified distance which would represent 

the maximum continuous distance of downstream dilution from the edge of the initial 

area of concern. This was not conducted for myclobutanil because all aquatic RQs with 

all modeled scenarios with myclobutanil and myclobutanil plus 1,2,4 triazole were lower 

that the related LOCs. 

The determination of the buffer distance for spatial extent of the effects determination is 

described below. 

5.2.5.1 Spray Drift 

In order to determine terrestrial and aquatic habitats of concern due to myclobutanil 

exposures through spray drift, it is necessary to estimate the distance that spray 

applications can drift from the treated area and still be present at concentrations that 

exceed levels of concern. An analysis of spray drift distances was completed using 

AgDrift (v. 2.01). 

 

Spatial analysis of spray drift effects is limited to consideration of a single application 

because, due to variable wind conditions, multiple applications are not likely to impact 

the same location each time. Spray drift distances depend on both application rate and 

method. The range of possible impacts was assessed by modeling uses with the highest 

and lowest single maximum application rate for each method of application that resulted 

in LOC exceedances. A turf grass use was modeled as the highest application rate for 

ground equipment. Mango and hops commodities were modeled as the highest rate for 

aerial application. A use on caneberries (e.g., boysenberry) was modeled for lowest 

single maximum application rate for both ground and aerial methods to represent a lower 

bound for potential impact. 

117
Myclobutanil labels do not have specific application requirements for reducing potential 

spray drift, that is, restrictions on wind speed, release height and droplet size. Therefore, 

conservative Tier I AgDrift default values are used for these inputs (Table 5.12). 

Table 5.12 Input Parameters for Simulation of Myclobutanil in Spray Drift Using 

AgDrift (v. 2.01) 

Parameter Description Turf Grass Mango Caneberry Caneberry 

Application Method Ground Aerial Ground Aerial 

Application Rate 1.3 0.25 0.0625 0.0625 

Droplet Size Distribution Very Fine to Fine - 90th Percentile 

Release Height High Boom NA High Boom NA 

Table 5.13 includes uses with the maximum single application rates for each application 

method and presents a summary of the buffer distances at which spray drift deposition 

from these uses drop below levels of concern (e.g., RQs will be below LOCs). The 

estimated buffer distance identifies those locations where terrestrial landscapes can be 

impacted by spray drift deposition alone (no runoff considered). These distances 

represent the maximum extent where effects are possible using the most sensitive 

terrestrial data and, in the case of myclobutanil, the chronic LOC of 1. The terrestrial 

analysis is based on the rat reproduction study NOAEL of 16 mg/kg bw/day, the most 

sensitive terrestrial endpoint. Using this endpoint and the highest rates for both aerial and 

ground applications, the estimated maximum distance at which any LOC for terrestrial 

species may be exceeded is 158 feet from the treated area for aerial applications and 76 

feet for ground applications. An analysis of potential risk to the aquatic-phase CRLF 

from spray drift was not conducted because no myclobutanil uses resulted in LOC 

exceedances for freshwater aquatic species. 

Table 5.13 Summary of Maximum Predicted Distances for Potential Spray Drift 

Effects 

Application Method Application Rate 

(lb/ai Acre) 

Uses Terrestrial LD50 

Distance (ft) 

0.5 Mango 158 Aerial 0.0625 Caneberries 0 

1.3 Turf Grass 76 Ground 0.0625 Caneberries 0 

5.2.5.2 Downstream Dilution Analysis 

Downstream dilution analysis is an approach used to estimate the downstream extent of 

exposure in streams and rivers where the EEC may be above levels that would exceed 

LOCs. As stated earlier, all aquatic RQs from all modeled scenarios with myclobutanil 

and myclobutanil plus 1,2,4 triazole were lower that the related LOCs. Therefore, given 

that no LOCs were exceeded, a downstream dilution analysis was not performed. 

118
5.2.5.3 Overlap between CRLF habitat and Spatial Extent of Potential 

Effects 

An LAA effects determination is made to those areas where it is expected that the 

pesticide’s use will directly or indirectly affect the CRLF or its designated critical habitat 

and the area overlaps with the core areas, critical habitat and available occurrence data 

for CRLF. 

For myclobutanil, the use pattern in the following land cover classes (cultivated crops, 

developed land (low, medium and high intensity and open space), forest, open water, 

orchards and vineyards, pasture/hay, wetlands, turf and rights-of-way) also includes areas 

beyond the initial area of concern that may be impacted by runoff and/or spray drift 

overlaps with CRLF habitat. When the footprint of the initial area of concern (which 

represents potential myclobutanil use sites) is compared to CRLF habitat, there are 

several areas of overlap (Figure 5.1). Appendix E provides maps of the initial area of 

concern, along with CRLF habitat areas, including currently occupied core areas, 

CNDDB occurrence sections, and designated critical habitat. It is expected that any 

additional areas of CRLF habitat that are located 158 ft (to account for offsite migration 

via spray drift) outside the initial area of concern may also be impacted and are part of 

the full spatial extent of the LAA/effects to critical habitat effects determination. 

119
Figure 5.1 Overlap Map: CRLF Habitat and Myclobutanil Initial Area of Concern 

120
6 Uncertainties 

6.1 Exposure Assessment Uncertainties 

6.1.1 Maximum Use Scenario 

The screening-level risk assessment focuses on characterizing potential ecological risks 

resulting from a maximum use scenario, which is determined from labeled statements of 

maximum application rate and number of applications with the shortest time interval 

between applications. The frequency at which actual uses approach this maximum use 

scenario may be dependant on pest resistance, timing of applications, cultural practices, 

and market forces. 

6.1.2 Aquatic Exposure Modeling of Myclobutanil 

The standard ecological water body scenario (EXAMS pond) used to calculate potential 

aquatic exposure to pesticides is intended to represent conservative estimates, and to 

avoid underestimations of the actual exposure. The standard scenario consists of 

application to a 10-hectare field bordering a 1-hectare, 2-meter deep (20,000 m3

) pond 

with no outlet. Exposure estimates generated using the EXAMS pond are intended to 

represent a wide variety of vulnerable water bodies that occur at the top of watersheds 

including prairie pot holes, playa lakes, wetlands, vernal pools, man-made and natural 

ponds, and intermittent and lower order streams. As a group, there are factors that make 

these water bodies more or less vulnerable than the EXAMS pond. Static water bodies 

that have larger ratios of pesticide-treated drainage area to water body volume would be 

expected to have higher peak EECs than the EXAMS pond. These water bodies will be 

either smaller in size or have larger drainage areas. Smaller water bodies have limited 

storage capacity and thus may overflow and carry pesticide in the discharge, whereas the 

EXAMS pond has no discharge. As watershed size increases beyond 10-hectares, it 

becomes increasingly unlikely that the entire watershed is planted with a single crop that 

is all treated simultaneously with the pesticide. Headwater streams can also have peak 

concentrations higher than the EXAMS pond, but they likely persist for only short 

periods of time and are then carried and dissipated downstream. 

The Agency acknowledges that there are some unique aquatic habitats that are not 

accurately captured by this modeling scenario and modeling results may, therefore, 

under- or over-estimate exposure, depending on a number of variables. For example, 

aquatic-phase CRLFs may inhabit water bodies of different size and depth and/or are 

located adjacent to larger or smaller drainage areas than the EXAMS pond. The Agency 

does not currently have sufficient information regarding the hydrology of these aquatic 

habitats to develop a specific alternate scenario for the CRLF. CRLFs prefer habitat with 

perennial (present year-round) or near-perennial water and do not frequently inhabit 

vernal (temporary) pools because conditions in these habitats are generally not suitable 

(Hayes and Jennings 1988). Therefore, the EXAMS pond is assumed to be representative 

121
of exposure to aquatic-phase CRLFs. In addition, the Services agree that the existing 

EXAMS pond represents the best currently available approach for estimating aquatic 

exposure to pesticides (USFWS/NMFS 2004). 

In general, the linked PRZM/EXAMS model produces estimated aquatic concentrations 

that are expected to be exceeded once within a ten-year period. The Pesticide Root Zone 

Model is a process or “simulation” model that calculates what happens to a pesticide in 

an agricultural field on a day-to-day basis. It considers factors such as rainfall and plant 

transpiration of water, as well as how and when the pesticide is applied. It has two major 

components: hydrology and chemical transport. Water movement is simulated by the use 

of generalized soil parameters, including field capacity, wilting point, and saturation 

water content. The chemical transport component can simulate pesticide application on 

the soil or on the plant foliage. Dissolved, adsorbed, and vapor-phase concentrations in 

the soil are estimated by simultaneously considering the processes of pesticide uptake by 

plants, surface runoff, erosion, decay, volatilization, foliar wash-off, advection, 

dispersion, and retardation. 

Uncertainties associated with each of these individual components add to the overall 

uncertainty of the modeled concentrations. Additionally, model inputs from the 

environmental fate degradation studies are chosen to represent the upper confidence 

bound on the mean values that are not expected to be exceeded in the environment 

approximately 90 percent of the time. Mobility input values are chosen to be 

representative of conditions in the environment. The natural variation in soils adds to the 

uncertainty of modeled values. Factors such as application date, crop emergence date, 

and canopy cover can also affect estimated concentrations, adding to the uncertainty of 

modeled values. Factors within the ambient environment such as soil temperatures, 

sunlight intensity, antecedent soil moisture, and surface water temperatures can cause 

actual aquatic concentrations to differ for the modeled values. 

Unlike spray drift, tools are currently not available to evaluate the effectiveness of a 

vegetative setback on runoff and loadings. The effectiveness of vegetative setbacks is 

highly dependent on the condition of the vegetative strip. For example, a wellestablished, healthy vegetative setback can be a very effective means of reducing runoff 

and erosion from agricultural fields. Alternatively, a setback of poor vegetative quality 

or a setback that is channelized can be ineffective at reducing loadings. Until such time 

as a quantitative method to estimate the effect of vegetative setbacks on various 

conditions on pesticide loadings becomes available, the aquatic exposure predictions are 

likely to overestimate exposure where healthy vegetative setbacks exist and 

underestimate exposure where poorly developed, channelized, or bare setbacks exist. 

In order to account for uncertainties associated with modeling, available monitoring data 

were compared to PRZM/EXAMS estimates of peak EECs for the different uses. As 

discussed above, several data values were available from NAWQA for myclobutanil, but 

not the 1,2,4-triazole degradate, concentrations measured in surface waters receiving 

runoff from agricultural areas. The specific use patterns (e.g. application rates and timing, 

crops) associated with the agricultural areas are unknown, however, they are assumed to 

122
be representative of potential myclobutanil use areas. The 1-in-10 year peak, and 21 and 

60-day running mean concentrations (EECs) for myclobutanil and myclobutanil plus 

1,2,4-triazole estimated by PRZM/EXAMS were all higher than the highest myclobutanil 

concentration observed in the USGS NAWQA (0.51 μg/L) monitoring data. The peak 

myclobutanil plus 1,2, 4-triazole concentrations ranged between 5.1 and 61.4 μg/L; the 

21-day means ranged from 15.1 to 61.2 μg/L and the 60-day mean ranged from 5.08 to 

60.7 μg/L, respectively. There are no detections of myclobutanil report in ground water 

in the NAQWA studies. 

Based upon the vapor pressure and Henry’s Law Constant, the transport of myclobutanil 

in the atmosphere vapor phase would not be expected. However, myclobutanil residues 

have been detected in rain water. The study by Vogel et al., 2008 attributed the 

myclobutanil to almonds. It is assumed that the reason for the detections are because 

fungicides are typically applied to almonds trees my air blast or aerial spray (Mosz, 2002) 

or that the myclobutanil is sorbed to wind blow soil particles.

6.1.3 Usage Uncertainties 

County-level usage data were obtained from California’s Department of Pesticide 

Regulation Pesticide Use Reporting (CDPR PUR) database. Four years of data (2002 – 

2005) were included in this analysis because statistical methodology for identifying 

outliers, in terms of area treated and pounds applied, was provided by CDPR for these 

years only. No methodology for removing outliers was provided by CDPR for 2001 and 

earlier pesticide data; therefore, this information was not included in the analysis because 

it may misrepresent actual usage patterns. CDPR PUR documentation indicates that 

errors in the data may include the following: a misplaced decimal; incorrect measures, 

area treated, or units; and reports of diluted pesticide concentrations. In addition, it is 

possible that the data may contain reports for pesticide uses that have been cancelled. 

The CPDR PUR data does not include home owner applied pesticides; therefore, 

residential uses are not likely to be reported. As with all pesticide usage data, there may 

be instances of misuse and misreporting. The Agency made use of the most current, 

verifiable information; in cases where there were discrepancies, the most conservative 

information was used. 

6.1.4 Terrestrial Exposure Modeling of Myclobutanil 

The Agency relies on the work of Fletcher et al. (1994) for setting the assumed pesticide 

residues in wildlife dietary items. These residue assumptions are believed to reflect a 

realistic upper-bound residue estimate, although the degree to which this assumption 

reflects a specific percentile estimate is difficult to quantify. It is important to note that 

the field measurement efforts used to develop the Fletcher estimates of exposure involve 

highly varied sampling techniques. It is entirely possible that much of these data reflect 

residues averaged over entire above ground plants in the case of grass and forage 

sampling. 

123
It was assumed that ingestion of food items in the field occurs at rates commensurate 

with those in the laboratory. Although the screening assessment process adjusts dryweight estimates of food intake to reflect the increased mass in fresh-weight wildlife food 

intake estimates, it does not allow for gross energy differences. Direct comparison of a 

laboratory dietary concentration- based effects threshold to a fresh-weight pesticide 

residue estimate would result in an underestimation of field exposure by food 

consumption by a factor of 1.25 – 2.5 for most food items. 

Differences in assimilative efficiency between laboratory and wild diets suggest that 

current screening assessment methods do not account for a potentially important aspect of 

food requirements. Depending upon species and dietary matrix, bird assimilation of wild 

diet energy ranges from 23 – 80%, and mammal’s assimilation ranges from 41 – 85% 

(U.S. Environmental Protection Agency, 1993). If it is assumed that laboratory chow is 

formulated to maximize assimilative efficiency (e.g., a value of 85%), a potential for 

underestimation of exposure may exist by assuming that consumption of food in the wild 

is comparable with consumption during laboratory testing. In the screening process, 

exposure may be underestimated because metabolic rates are not related to food 

consumption. 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal 

was assumed to occupy either the treated field or adjacent areas receiving a treatment rate 

on the field. Actual habitat requirements of any particular terrestrial species were not 

considered, and it was assumed that species occupy, exclusively and permanently, the 

modeled treatment area. Spray drift model predictions suggest that this assumption leads 

to an overestimation of exposure to species that do not occupy the treated field 

exclusively and permanently. 

6.1.5 Spray Drift Modeling 

Although there may be multiple myclobutanil applications at a single site, it is unlikely 

that the same organism would be exposed to the maximum amount of spray drift from 

every application made. In order for an organism to receive the maximum concentration 

of myclobutanil from multiple applications, each application of myclobutanil would have 

to occur under identical atmospheric conditions (e.g., same wind speed and – for plants – 

same wind direction) and (if it is an animal) the animal being exposed would have to be 

present directly downwind at the same distance after each application. Although there 

may be sites where the dominant wind direction is fairly consistent (at least during the 

relatively quiescent conditions that are most favorable for aerial spray applications), it is 

nevertheless highly unlikely that plants in any specific area would receive the maximum 

amount of spray drift repeatedly. It appears that in most areas (based upon available 

meteorological data) wind direction is temporally very changeable, even within the same 

day. Additionally, other factors, including variations in topography, cover, and 

meteorological conditions over the transport distance are not accounted for by the 

AgDRIFT model (i.e., it models spray drift from aerial and ground applications in a flat 

124
area with little to no ground cover and a steady, constant wind speed and direction). 

Therefore, in most cases, the drift estimates from AgDRIFT may overestimate exposure 

even from single applications, especially as the distance increases from the site of 

application, since the model does not account for potential obstructions (e.g., large hills, 

berms, buildings, trees, etc.). Furthermore, conservative assumptions are often made 

regarding the droplet size distributions being modeled (e.g.: ‘ASAE Very Fine to Fine’ 

for all uses), the application method (e.g., aerial), release heights and wind speeds. 

Alterations in any of these inputs would change the area of potential effect. 

6.2 Effects Assessment Uncertainties 

6.2.1 Age Class and Sensitivity of Effects Thresholds 

It is generally recognized that test organism age may have a significant impact on the 

observed sensitivity to a toxicant. The acute toxicity data for fish are collected on 

juvenile fish between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on 

recommended immature age classes (e.g., first instar for daphnids, second instar for 

amphipods, stoneflies, mayflies, and third instar for midges). 

Testing of juveniles may overestimate toxicity at older age classes for pesticide active 

ingredients that act directly without metabolic transformation because younger age 

classes may not have the enzymatic systems associated with detoxifying xenobiotics. In 

so far as the available toxicity data may provide ranges of sensitivity information with 

respect to age class, this assessment uses the most sensitive life-stage information as 

measures of effect for surrogate aquatic animals, and is therefore, considered as 

protective of the CRLF. 

6.2.2 Use of Surrogate Species Effects Data 

Guideline toxicity tests and open literature data on myclobutanil are not available for 

frogs or any other aquatic-phase amphibian; therefore, freshwater fish are used as 

surrogate species for aquatic-phase amphibians. Endpoints based on freshwater fish 

ecotoxicity data are assumed to be protective of potential direct effects to aquatic-phase 

amphibians including the CRLF, and extrapolation of the risk conclusions from the most 

sensitive tested species to the aquatic-phase CRLF is likely to overestimate the potential 

risks to those species. Efforts are made to select the organisms most likely to be affected 

by the type of compound and usage pattern; however, there is an inherent uncertainty in 

extrapolating across phyla. In addition, the Agency’s LOCs are intentionally set very 

low, and conservative estimates are made in the screening level risk assessment to 

account for these uncertainties.

6.2.3 Sublethal Effects 

When assessing acute risk, the screening risk assessment relies on the acute mortality 

endpoint as well as a suite of sublethal responses to the pesticide, as determined by the 

125
testing of species response to chronic exposure conditions and subsequent chronic risk 

assessment. Consideration of additional sublethal data in the effects determination t is 

exercised on a case-by-case basis and only after careful consideration of the nature of the 

sublethal effect measured and the extent and quality of available data to support 

establishing a plausible relationship between the measure of effect (sublethal endpoint) 

and the assessment endpoints. However, the full suite of sublethal effects from valid 

open literature studies is considered for the purposes of defining the action area. 

No sublethal effects related to this assessment were available in the open literature. To 

the extent to which sublethal effects are not considered in this assessment, the potential 

direct and indirect effects of myclobutanil on CRLF may be underestimated. 

6.2.4 Location of Wildlife Species 

For the terrestrial exposure analysis of this risk assessment, a generic bird or mammal 

was assumed to occupy either the treated field or adjacent areas receiving a treatment rate 

on the field. Actual habitat requirements of any particular terrestrial species were not 

considered, and it was assumed that species occupy, exclusively and permanently, the 

modeled treatment area. Spray drift model predictions suggest that this assumption leads 

to an overestimation of exposure to species that do not occupy the treated field 

exclusively and permanently. 

6.2.5 Use of Surrogate Chemical Effects Data 

Guideline toxicity tests and open literature data on myclobutanil were not available for 

aquatic invertebrate (chronic exposure), aquatic vascular plants, or terrestrial plants. In 

lieu of any myclobutanil data, toxicity data from other conazole (DMI triazole) 

fungicides were used to characterize risk, assuming that myclobutanil toxicity is similar 

to other conazoles due to similar mode of action. In so far as data from other conazoles 

provides a range of sensitivity for conazole fungicides, there is considerable uncertainty 

associated with extrapolating toxicity from other conazoles to myclobutanil. Thus, the 

effects of myclobutanil cannot be quantified without data on myclobutanil toxicity to 

aquatic invertebrates, aquatic vascular plants, and terrestrial plants. 

7 Risk Conclusions 

In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the 

information presented in this endangered species risk assessment represents the best data 

currently available to assess the potential risks of myclobutanil to the CRLF and its 

designated critical habitat. 

Based on the best available information, the Agency makes a “Likely to Adversely 

Affect” determination for the CRLF from the use of myclobutanil. The Agency has also 

determined that there is the potential for effects to CRLF designated critical habitat from 

the use of the chemical. The CRLF and/or its critical habitat may be affected for all uses. 

126
This assessment indicates that direct effects to the terrestrial-phase CRLF eating small 

herbivorous mammals on a dose-basis may be at risk following acute exposure to 

myclobutanil at application rates of 0.12 lb a.i./A and above (most crops and turf; cotton 

seed treatment). In addition, the terrestrial-phase CRLF eating small invertebrates on a 

dietary basis may be at risk for direct effects following chronic exposure to myclobutanil 

applied to cotton (0.06 lb a.i./cwt) and turf at 1.3 lbs a.i./A. Direct effects on the aquaticphase CRLF are not expected. 

Indirect effects to the terrestrial-phase CRLF, based on reduction in prey base may occur 

with terrestrial phase amphibians on a dose-basis following acute exposure at application 

rates of 0.12 lb a.i./A and above (most crops, cotton and turf) and on a dietary-basis 

following chronic exposure at an application rate of 1.3 lbs a.i./A (turf) and when applied 

to cotton (0.06 lb a.i./cwt). Indirect effects (reduction in prey base) may also occur with 

mammals following acute exposure on a dose-basis at application rates of 0.25 lb a.i./A 

and above (apple, apricot, cherry, nectarine, peach, hops and turf uses) and chronic 

exposure on a dose-basis at application rates of 0.0625 lbs a.i./A and above (e.g., all uses) 

and on a dietary-basis of 0.25 lbs a.i./A and above (apples, apricots, cherries, nectarines, 

peaches, cotton and turf). Indirect effects to the aquatic-phase CRLF, based on reduction 

in prey base are not expected. Minimal potential indirect impact to the CRLF via effects 

of myclobutanil on terrestrial invertebrate food items is expected. No effects were 

observed with aquatic non-vascular plants and with aquatic invertebrates following acute 

exposure. No chronic data are available for aquatic invertebrates. The weight of the 

evidence, including chronic data from similar conazole pesticides indicates that although 

myclobutanil may affect the aquatic invertebrate population following chronic exposure, 

it is not expected to adversely affect the population. 

Indirect effects to both the aquatic- and terrestrial-phase CRLF based on aquatic and 

riparian habitat, cover and/or primary productivity (e.g., effects on aquatic and terrestrial 

plants) may occur due to potential effects on the riparian terrestrial plant community. As 

stated previously, no effects were observed with aquatic non-vascular plants. No data are 

available for either aquatic vascular or terrestrial plants. For aquatic vascular plants, the 

weight of the evidence, including plant data from similar conazole pesticides indicates 

that although there may be effects with some of the registered myclobutanil uses, adverse 

affects are not expected. For terrestrial plants, weight of the evidence from information 

provided in the open literature, incident data and the fact that surrogate data from similar 

fungicides would exceed the terrestrial plant LOC for many of the myclobutanil uses, it is 

determined that effects to terrestrial plants may affect the CRLF via habitat effects. Based 

on potential effects to the avian/terrestrial-phase amphibian, mammalian and terrestrial 

plant populations, there is a potential for habitat effects associated with all 4 of the 

terrestrial-phase PCE’s: elimination and/or disturbance of upland habitat and ability of 

habitat to support food source of CRLFs, elimination and/or disturbance of dispersal 

habitat, reduction and/or modification of food sources for terrestrial phase juveniles and 

adults and alteration of chemical characteristics necessary for normal growth and 

viability of juvenile and adult CRLFs and their food source. 

127
Given the LAA determination for the CRLF and potential effects to designated critical 

habitat, a description of the baseline status and cumulative effects for the CRLF is 

provided in Attachment 2.

The LAA effects determination applies to those areas where it is expected that the 

pesticide’s use will directly or indirectly affect the CRLF or its designated critical habitat. 

To determine this area, the footprint of myclobutanil’s use pattern is identified, using 

corresponding land cover data. The spatial extent of the LAA effects determination also 

includes areas beyond the initial area of concern that may be impacted by runoff and/or 

spray drift. The identified direct and indirect effects and/or effects to critical habitat are 

anticipated to occur only for those currently occupied core habitat areas, CNDDB 

occurrence sections, and designated critical habitat for the CRLF that overlap with the 

initial area of concern plus 158 feet from its boundary (see Section 5.1.4 for further 

analysis). It is assumed that non-flowing waterbodies (or potential CRLF habitat) are 

included within this area. 

Appendix E provides maps of the initial area of concern, along with CRLF habitat areas, 

including currently occupied core areas, CNDDB occurrence sections, and designated 

critical habitat. It is expected that any additional areas of CRLF habitat that are located 

158 ft (to account for offsite migration via spray drift) outside the initial area of concern 

may also be impacted and are part of the full spatial extent of the LAA/effects to critical 

habitat determination. 

A summary of the risk conclusions and effects determinations for the CRLF and its 

critical habitat, given the uncertainties discussed in Section 6, is presented in Table 7.1 

and Table 7.2. 

Table 7.1 Effects Determination Summary for Myclobutanil Use and the CRLF 

Assessment 

Endpoint 

Effects 

Determination 1

Basis for Determination 

Potential for Direct Effects

Aquatic-phase (Eggs, Larvae, and Adults): 

Acute and chronic freshwater fish RQs are below the respective level of concern 

(LOC) for all uses of myclobutanil. 

Terrestrial-phase (Juveniles and Adults): 

The acute avian LOC is exceeded at application rates of 0.12 lb a.i./A and above 

(most crops, cotton and turf). The highest probabilities of an individual effect 

range from 1 in ~ 3.88E+02 to 1 in ~ 1. The chronic avian LOC is exceeded 

following uses on cotton (0.06 lb a.i./cwt) and turf at 1.3 lbs a.i./A. Myclobutanil 

uses overlap CRLF habitat. 

Potential for Indirect Effects

Survival, growth, 

and/or reproduction 

of CRLF 

individuals 

LAA1

Aquatic prey items, aquatic habitat, cover and/or primary productivity 

Acute and chronic freshwater fish RQs are below the respective LOC for all uses 

of myclobutanil. 

128
Assessment 

Endpoint 

Effects Basis for Determination 

Determination 1

Acute freshwater invertebrate RQs are below the LOC for all uses of 

myclobutanil. No chronic freshwater invertebrate studies are available for 

myclobutanil. Weight of the evidence from RQs based on myclobutanil EECs 

and toxicity data from 9 other conazole fungicides indicates that minimal impact 

is expected from chronic exposure to freshwater invertebrates as prey items. 

Acute RQs for aquatic non-vascular plants for all uses of myclobutanil are below 

the LOC. No aquatic vascular plant studies are available. Weight of the 

evidence from RQs based on myclobutanil EECs and toxicity data from 7 other 

conazole fungicides indicates minimal impact to the CRLF aquatic habitat, cover 

and/or primary productivity. 

Terrestrial prey items, riparian habitat 

See description above for direct effects on birds as surrogate for terrestrial phase 

amphibians. LOCs for listed mammals exceeded following acute exposure at 

application rates of 0.25 lb a.i./A and above and chronic exposure on at 

application rates of 0.0625 lbs a.i./A and above. Percent effect on mammalian 

population is estimated to range from 4 – 42% for the myclobutanil uses. 

Myclobutanil uses overlap CRLF habitat. 

For terrestrial invertebrates, the honeybee acute contact data show no mortalities 

at concentration levels up to and including 2836 ppm (highest level tested), 

which is higher than highest dietary-based EEC for small insects with the use on 

turf; however, there is some uncertainty for potential mortality. For large 

invertebrates, there is no concern. Based on the results of the honey bee study 

and weight of the evidence from open literature studies, indirect impact to the 

CRLF via effects of myclobutanil on terrestrial invertebrate food items is 

expected to be minimal. 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 1

 No effect (NE); May affect, but not likely to adversely affect (NLAA); May affect, likely to adversely 

affect (LAA)

Table 7.2 Effects Determination Summary for Myclobutanil Use and CRLF Critical 

Habitat Impact Analysis 

Assessment 

Endpoint 

Effects 

Determination 

Basis for Determination 

Modification of 

aquatic-phase PCE Habitat Effects Acute RQs for aquatic non-vascular plants for all uses of myclobutanil are below 

the LOC. 

No aquatic vascular plant studies are available. Weight of the evidence from 

RQs based on myclobutanil EECs and toxicity data from 7 other conazole 

fungicides indicates minimal impact to the CRLF aquatic habitat. 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

129
Assessment 

Endpoint 

Effects Basis for Determination 

Determination 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 

Acute and chronic freshwater fish RQs are below the respective level of concern 

(LOC) for all uses of myclobutanil. 

Indirect effects to the CRLF through effects to its prey in the aquatic habitat 

(freshwater invertebrates) are expected to be minimal (see table 1.1). 

Modification of 

terrestrial-phase 

PCE 

No acceptable terrestrial plant studies are available. RQs based on EECs and 

toxicity data from 5 other conazole fungicides indicate that most uses may affect 

terrestrial plants, particularly dicots in semi-aquatic areas. Weight of the 

evidence from these data, the open literature and incident reports indicates that 

these effects may have an impact on riparian habitat. 

The acute avian LOC is exceeded at application rates of 0.12 lb a.i./A and above 

(most crops, cotton and turf). The chronic avian LOC is exceeded following uses 

on cotton (0.06 lb a.i./cwt) and turf at 1.3 lbs a.i./A. 

LOCs for listed mammals exceeded following acute exposure on a dose-basis for 

many crops and chronic exposure on a dose-basis for all uses and on a dietarybasis for many crops. 

For terrestrial invertebrates, the weight of the evidence indicates that minimal 

potential indirect impact to the CRLF via effects on terrestrial invertebrate food 

items is expected. 

Based on the conclusions of this assessment, a formal consultation with the U. S. Fish 

and Wildlife Service under Section 7 of the Endangered Species Act should be initiated. 

When evaluating the significance of this risk assessment’s direct/indirect and habitat 

effects determinations, it is important to note that pesticide exposures and predicted risks 

to the species and its resources (i.e., food and habitat) are not expected to be uniform 

across the action area. In fact, given the assumptions of drift and downstream transport 

(i.e., attenuation with distance), pesticide exposure and associated risks to the species and 

its resources are expected to decrease with increasing distance away from the treated field 

or site of application. Evaluation of the implication of this non-uniform distribution of 

risk to the species would require information and assessment techniques that are not 

currently available. Examples of such information and methodology required for this 

type of analysis would include the following: 

• Enhanced information on the density and distribution of CRLF life stages within 

specific recovery units and/or designated critical habitat within the action area. 

This information would allow for quantitative extrapolation of the present risk 

assessment’s predictions of individual effects to the proportion of the population 

extant within geographical areas where those effects are predicted. Furthermore, 

such population information would allow for a more comprehensive evaluation of 

the significance of potential resource impairment to individuals of the species. 

130
• Quantitative information on prey base requirements for individual aquatic- and 

terrestrial-phase frogs. While existing information provides a preliminary picture 

of the types of food sources utilized by the frog, it does not establish minimal 

requirements to sustain healthy individuals at varying life stages. Such 

information could be used to establish biologically relevant thresholds of effects 

on the prey base, and ultimately establish geographical limits to those effects. 

This information could be used together with the density data discussed above to 

characterize the likelihood of adverse effects to individuals. 

• Information on population responses of prey base organisms to the pesticide. 

Currently, methodologies are limited to predicting exposures and likely levels of 

direct mortality, growth or reproductive impairment immediately following 

exposure to the pesticide. The degree to which repeated exposure events and the 

inherent demographic characteristics of the prey population play into the extent to 

which prey resources may recover is not predictable. An enhanced understanding 

of long-term prey responses to pesticide exposure would allow for a more refined 

determination of the magnitude and duration of resource impairment, and together 

with the information described above, a more complete prediction of effects to 

individual frogs and potential effects to critical habitat. 

131
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