UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

APR 2 8 2014 

OFFICE OF CHEMICAL 

SAFETY 

. AND POLLUTION 

PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

Use and Usage, Pest Management Role, and Response to Comrp.ents for 

Hexythiazox (PC 128849) in Support of Registration Review 

Clayton Myers, Ph.D, Biologist-tl 

Biological Analysis Branch ~\ 

Elizabeth Hill, Economist 

Economic Analysis Branch 

Jihad 

Science 

Alsadek, 

Information 

Ph.D, 

and 

Economist 

Analysis 

~ Branch A- .. A~ 

Biological and Economic Analysis Division (7503P) 

Arnet Jones, Chief ~ 

:::::. ::rsis Brnn(\_ ~ , 

Economic Analysis Branc'kJ J 

Diann Sims, Chie~ ~-'0t-~""'P.i..­ Science Information and Anal is Branch 

Biological and Economic Analysis Division (7503P) 

Molly Clayton, Chemical Review Manager 

Risk Management and Implementation Branch 3 (RMIB 3) 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel: Apri123, 2014 

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SUMMARY 

Hexyt:hiazox is in the proposed decision making phase of registration review. BEAD is 

providing here use/usage, IPM/alternatives information, and responses to public comments to 

help inform risk management decisions. 

Hexyt:hiazox is an IRAC Group 10 miticide registered for use on various fruit, nut, vegetable, 

and row crops, as well as on turf, and residential plants, with applications limited to once per 

year. It can be applied as a liquid foliar spray by air or ground application equipment. The most 

recent Screening Level Usage Analysis (SLUA) data (2004-2012) show that the most significant 

usage is on almonds, strawberries, stone fruits, caneberries, dates, tangerines, and walnuts. 

While hexythiazox can be applied. at almost any time in the growing season, its ovicidal activity 

lends itself to mostly early season applications targeting the egg stage of phytophagous mites. 

While there are a number of alternative miticides available for the pest mite species in the 

activity spectrum for hexythiazox, there are relatively few ovicides. Clofentazine and etoxazole 

are other Group 1 0 ovicidal chemicals that are thought to have a similar mode of action and pest 

spectrum. However, not all crops have registrations for these alternatives. For dates, citrus, 

alfalfa (hay production) and sweet corn, hexythiazox is the only ovicidal chemical registered for 

mite control. Costs of application of hexythiazox are comparable to etoxazole. 

BEAD'S USE/USAGE DATA 

Hexythiazox labels limit applications to once per year on all crops. OPP's Screening Level 

Usage Analysis (SLUA) (OPP/BEAD, 2014) indicates that more than 20 surveyed crops are 

treated with hexyt:hiazox. The data show 25% of strawberries are treated, 15% each for 

cane berries, dates, tangerines and nectarines, 10% each for almonds and peaches, and 5% each 

for apricots, plums/prunes and walnuts are treated with hexythiazox Pluots are also treated, but a 

percent treated value was not calculated for this crop, which were derived solely from California 

data. The remaining surveyed crops are treated at an average of less than 2.5% of acreage, 

respectively. Total annual agricultural usage averaged 25,000 lbs per year for the time period 

2004-2012 with almonds accounting for the highest percentage of total pounds applied, with an 

average of 10,000 lbs applied annually over the same time period (OPP/BEAD, 2014). By 

comparison, overall nursery and floriculture usage was reported as 1 ,500 lbs in 2006 and 700 lbs 

in 2009 (USDA/NASS, 2009). 

Available use data for hexythiazox from 2008-2012 (EPA Proprietary Data, 2014) show that 

average application rates for hexythiazox are below the maximum label application rates, except 

for pecans, and that use was less than 100 lbs and only in one year. While hexythiazox is applied 

by both ground and aerial application, use data from 2008-2012 show that only for almonds in 

2011 and 2012 was the average aerial application rate equal to the maximum label application 

rate. For some years, ground applications to caneberries, cherries, grapes and pecan show 

average rates equal to the maximum label rate, but not consistently so. For most crops, ground 

applications are made at rates below the respective maximum label application rates. Table 1 

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below lists the average application rates ofhexythiazox by crop for the time period 2008-2012. 

Please note that this table was derived from an independent usage query (EPA Proprietary Data) 

and thus, might not exactly match the figures listed for EPA's SLUA (OPP/BEAD 2014), which 

captured a different time frame and included California crops not surveyed in EPA's proprietary 

data source. 

T a bl e . 1 A verage AIRtbC a e )y rop ti or H exy1 th" Iazox, 2008 -2012 

Average AI Rate/ Acre, 

Crop (2008-2012, Calculated Annually) 

Apples 0.13 

Pears 0.15 

Cane berries 0.18 

Strawberries 0.17 

Com 0.09 

Sweet Com 0.13 

Grapes, Raisin 0.16 

Grapes, Table 0.16 

Grapes, Wine 0.12 

Dry Beans/Peas 0.02 

Beans (Snap, Bush, Pole, String) 0.16 

Walnuts 0.14 

Pecans 0.19 

Almonds 0.14 

Tomatoes 0.09 

Potatoes 0.06 

Cherries 0.15 

Peaches 0.14 

Plums/Prunes 0.14 

Oranges 0.15 

Source: EPA Propnetary Data, 2008-2012. 

IPM IMPORTANCE AND ALTERNATIVES 

Hexythiazox is classified by the Insecticide Resistance Action Committee (IRA C) as a Group 10 

miticide. Group 10 is a somewhat nebulous IRAC classification referred to as "mite growth 

inhibitors." While the specific modes of action have not been well-described for this group, 

hexythiazox, clofentazine, and etoxazole are presumed to have similar modes of action due to 

observed cross-resistance and shared ovicidal activity (IRAC, 2014). 

Hexythiazox, like the other Group 10 miticides, has mostly ovicidal activity and has little to no 

efficacy against adult mites. Hexythiazox is known to be very effective against the eggs of 

phytophagous mites, including European red mites, two-spotted spider mites and other major 

pest species. Ovicidal efficacy of these miticides is well-documented in extension literature, and 

for several of the crops where both are registered, hexythiazox and clofentazine are 

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recommended as functionally equal materials for mite control. While hexythiazox can be 

applied at any time that mites are actively laying eggs, most pest management recommendations, 

especially for specialty crops including citrus (UC, 2008), caneberries (UC, 2010a) strawberries 

(Burrack et al., 2012; UC, 2010b), and almonds (UC, 2012) suggest early season application 

timing (sometimes during or immediately following bloom) in order to reduce subsequent mite 

outbreaks later in the growing season. 

While for many crops there are a number of other registered miticide alternatives that target 

adults and that make effective resistance management partners (i.e., materials in several other 

IRAC groups), there are no other registered ovicides outside of the Group 10 chemicals: 

hexythiazox, clofentazine, and etoxazole. For some crops, not all ofthese Group 10 chemicals 

are registered for use. For dates, citrus, sweet com, and alfalfa (grown for hay) in particular, 

hexythiazox is the only registered Group 10 chemical that is available for use. 

Prior to eventual Section 3 registrations, emergency exemptions were reviewed by EPA under 

FIFRA Section 18 for uses on strawberries (Burr and Hernandez, 1997; Gross and Halvorson, 

2000), hops (Gross and Halvorson, 1998), dates (Halvorson and Hennessey, 1998), cotton (Gross 

and Halvorson, 1997), com (Brassard and Faulkner, 2004) and sweet com grown for seed 

(Mallampalli and Faulkner, 2009, 2010). Minimally, this indicates that in the past there have 

been few available miticide alternatives for some crops and that urgent needs have existed for 

use of this chemical for mite control. 

Relative to other Group 10 miticide alternatives, the cost of application for hexythiazox is 

comparable to the alternative ovicide etoxazole (typically $40-55 per acre for most crops, 

depending on the application rates), but more expensive than clofentazine, which averages $10-

20 less per acre for some crops (EPA Proprietary data, 2014). Clofentazine, while cheaper per 

acre, is not registered on as many crops as either hexythiazox or etoxazole. On the whole, 

hexythiazox and etoxazole both have a higher average cost per acre than some of the adulticidal 

alternatives such as abamectin, spirodiclofen, pyridaben, and fenbutatin oxide. However, some 

adulticides may be applied multiple times, depending upon both population pressure and the 

success of early season mite management efforts. So in some instances, one successful early 

season application of a more narrow-spectrum and expensive ovicide such as hexythiazox can 

preclude the need for subsequent additional applications of adulticidal alternatives due to both 

efficacy against the target pest and conservation of beneficial predator species. 

BEAD'S RESPONSE TO COMMENTS 

EP A-OPP received public comments in response to the posting of Hexythiazox work plans and 

documents to docket EPA-HQ-OPP-2006-0114-0023. In this section, BEAD is responding to 

two comments related to the usage and benefits of hexythiazox, submitted with regard to the 

registration review process. 

Washington Hop Commission Comment, Apri/13, 2007: "Hexythiazox is an extremely 

important pest management tool for the US. hop industry for controlling Two-spotted spider 

mite (I'etranychus urticae), which is a major pest of the crop. We have very limited registered 

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plant protection tools for this pest, which is an annual problem on nearly 100% of US acreage. 

Hexythiazox is a very effective ovicide (all other registered miticides primarily target motile 

forms of this pest). It is important for resistance management programs, and fits extremely well 

with the hop industry's /PM strategies, including conservation biocontrol. Due to hexythiazox's 

relative level of safety to important predator species, it can be used with minimal disruption of 

beneficial populations. Loss of this product would seriously jeopardize the ability to control 

mites on nearly 30,000 acres of US. hops, located in the Pacific Northwest. This represents 

100% of US. commercial hop production and nearly 30% of the world's supply." 

BEAD Response: BEAD appreciates the information on the importance of hexythiazox for 

control of two-spotted spider mite on hops and the prevalence of this pest throughout the hop 

growing region of the United States. Based upon published efficacy ratings and extension 

recommendations for other crops, BEAD concurs that hexythiazox is an effective ovicidal 

material for control of this and other phytophagous mite pests. BEAD notes that a number of 

extension publications rate hexythiazox as having low toxicity to beneficial mites and predator 

species, albeit mainly via field observations rather than laboratory toxicology studies. BEAD 

notes that etoxazole, another IRAC Group 10 miticide with ovicidal activity is now registered for 

use on hops, so this would serve as one ovicidal alternative for hops producers. In general, 

references directing us to additional relative performance data are helpful if/when BEAD is 

asked to conduct a benefit assessment. 

National Alfalfa and Forage Alliance Comment, September 10, 2013: "Hexythiazox is a 

critically important insect management tool which provides effective control of the two-spotted 

spider mite in alfalfa seed The two-spotted spider mite can prove to be a serious arthropod pest 

for Western US. alfalfa seed producers. Hexythiozox (sic) is a selective ovicidal acaricide with a 

completely different mode of action than other registered acaricides. When hexythiazox (sic) is 

applied to spider mite infested alfalfa seed fields it suppresses populations of targeted 

pestiferous spider mites but does little or no harm to the predatory mites and other beneficial 

arthropods that aid in the natural biological regulation of arthropod pests. Spider mites are 

destructive pests which can significantly affect alfalfa seed yields. An actively feeding adult 

female can ingest a mass of plant tissue equivalent to her body weight in as little as two hours. It 

is estimated that a single mite can puncture and empty 100 photosynthetically active leaf cells 

per minute. In the Pacific Northwest, most seed producers use IP M strategies, which include 

monitoring spider mite and beneficial predatory mite populations within their fields. Growers 

only choose to apply an acaricide like hexythiazox (sic) when spider mite populations appear to 

be on the verge of outbreak early in the seed production season. Hexythiozox (sic) also provides 

better environmental safety compared to other acaricides registered for use on alfalfa seed " 

BEAD Response: BEAD appreciates the information on the importance of hexythiazox for 

control of two-spotted spider mite on alfalfa grown for seed, on the impact of damage from 

spider mites to yields of alfalfa seed, and on typical timing and threshold information for 

applications of hexythiazox. Based upon published efficacy ratings and extension 

recommendations for other crops, BEAD concurs that hexythiazox is an effective ovicidal 

material for control of this and other phytophagous mite pests. BEAD notes that there are other 

miticides that confer ovicidal efficacy in IRAC Group 10, including etoxazole, which is also 

registered for use on alfalfa grown for seed. BEAD notes that a number of extension 

5 
publications rate hexythiazox as having low toxicity to beneficial mites and predator species, 

albeit mainly via field observations rather than laboratory toxicology studies. In general, 

references directing us to additional relative performance data are helpful if/when BEAD is 

asked to conduct a benefit assessment. 

REFERENCES 

Brassard, D., and J. Faulkner, 2004. Review of a Request for Emergency Exemption of 

Hexythiazox in Texas for Use on Com to Control Mites. OPP-BEAD Memorandum, July 29, 

2004. 

Burr, W. F., and F. Hernandez, 1997. Emergency Exemption Request from the California 

Department of Pesticide Regulation for the Use of Hexythiazox (Savey) on Strawberries (97-CA45). OPP-BEAD Memorandum, August 20, 1997. 

Burrack, et al., 2012. Southeast Regional Strawberry Integrated Pest Management Guide, 

Entomology Section. 

http://www.smallfruits.org/SmallFruitsRegGuide/Guides/20 12/2012 strawberry.pdf 

EPA, 2014. Proprietary Data. 

Gross, W., and A. Halvorson, 1997. Review of the Emergency Exemption Request from 

California (97-CA-31) for Use ofHexythiazox (Savey) to Control Spider Mites on Cotton. OPPBEAD Memorandum, June 2, 1997. 

Gross, W., and A. Halvorson, 1998. BEAD's Review ofDocumentation in Support of an 

Emergency Exemption for the Use ofHexythiazox (Savey) and Cyhexatin (Pennsty) to Control 

the Two-Spotted Spider Mites on Hops in Idaho, Oregon, and Washington. OPP-BEAD 

Memorandum, April 8, 1998. 

Gross, W., and A. Halvorson, 2000. BEAD's Review of Documentation Submitted in Support of 

an Emergency Exemption for the Use ofHexythiazox (Savey) to Control Two-spotted Spider 

Mites on Florida Strawberries (00-FL-04). OPP-BEAD Memorandum, March 21,2000. 

Halvorson, A., and M. Hennessey, 1998. BEAD Review ofEmergency Exemption Application 

from the State of California for Hexythiazox (Savey) Against Banks Grass Mite on Dates. OPPBEAD Memorandum, April 2, 1998. 

IRAC, 2014. Insecticide Resistance Action Committee Mode of Action Classification Scheme, 

Updated February 2014. http://www.irac-online.org/documents/moa-classification/?ext=pdf 

Mallampalli, N., and J. Faulkner, 2009. Review of an Emergency Exemption Request for 

Hexythiazox in Idaho for Use On Sweet Com Grown for Seed to Control Mites (09-ID-04). 

OPP-BEAD Memorandum, June 8, 2009. 

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Mallampalli, N. and J. Faulkner, 2010. Review of an Emergency Exemption Request for 

Hexythiazox in Idaho for Use on Sweet Com Grown for Seed to Control Mites (10-ID-03). 

OPP-BEAD Memorandum, M~y 27, 2010. 

OPP/BEAD, 2014. Screening Level Usage Analysis (SLUA), Hexythiazox. 

UC, 2008. University of California IPM Pest Management Guidelines, Two-spotted Spider 

Mite, Citrus. Updated September, 2008. http://www.ipm.ucdavis.edu/PMG/r10740021l.html 

UC, 2010a. University of California IPM Pest Management Guidelines, Two-spotted Spider 

Mite, Caneberries. Updated March, 2010. http://www.ipm.ucdavis.edu/PMG/r714002ll.html 

UC, 2010b. University of California IPM Pest Management Guidelines, Spider Mites, 

Strawberries. Updated May, 2010. http://www.ipm.ucdavis.edu/PMG/r734400 lll.html 

UC, 2012. University of California IPM Pest Management Guidelines, Webspinning Spider 

Mites, Almonds. Updated November, 2012. http://www.ipm.ucdavis.edu/PMG/r3400211.html 

USDA-NASS, 2009. NASS Nursery and Floriculture Chemical Usage Query, 

http://www.nass.usda.gov/Data and Statistics/PreDefined Queries/2009 Nursery and Floriculture Chern Usage/index.asp 

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