UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

FEB 01 2012 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: BEAD Chemical Profile for Registration Review: Simazine (080807) 

FROM: 

THRU: 

TO: 

Bill Phillips, PhD, Agronomist lit!//' 

Biological Analysis Branch <IJJJI 

Jihad Alsadek, Economist .;/~ ~ /1- .... ~k . 

Science Information and Analysis Branch 

Molly Clayton, Chemical Review Manager 

Risk Management and Implementation Branch 3 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: January 23, 2013 

INTRODUCTION 

The purpose of this document is to convey usage information and a broad overview of the pest 

management roles of pesticides that are beginning to undergo registration review. The 

anticipated audience consists of the team of EPA staff currently evaluating the registration status 

1 
of simazine, and eventually the general public. This document builds upon the data already 

provided in the usage and label use data packages that are also provided to Registration Review 

teams by BEAD. The document is based on information and data available to BEAD as of 

January 23, 2013. 

HISTORY OF BEAD ASSESSMENTS FOR SIMAZINE 

A search of the BEAD Official Records database and the Office of Pesticide Programs FIFRA 

Section 18 Emergency Exemption data base did not find any benefits assessments or Section 18 

emergency exemptions requests specifically for simazine. In April of2006 simazine went 

through the Environmental Protection Agency registration eligibility decision (RED) where it 

was determined that " ... with label amendments and changes as specified in this document and 

the 2003 IRED for atrazine, there is a reasonable certainty that no harm will result to the 

general US. population, infants, children, or other major identifiable subgroups of consumers, 

from the use ofsimazine, atrazine, andpropazine." 1 

HERBICIDE DISCUSSION 

Simazine is a triazine herbicide in the Weed Science Society of America, group 5 with the 

mechanism of action of inhibiting photosynthesis at photosystem II. Simazine can be used 

postemergence to the weed as a foliar applied herbicide, however since it is readily absorbed 

through the root system, it is primarily applied as a pre-plant incorporated or soil applied 

herbicide. On average, over the period of 2000 to 20 I 0 the highest use in percent of total pounds 

of active ingredient was in com (53%) with the second highest percent of total use in oranges 

(22%). This herbicide is important in crop production as it is able to control grass and some 

broadleaf weeds in grass crops such as com, and in other crops such as tree fruits like oranges. 

Corn Production 

Many of the preemergence uses and characteristics of simazine are close to that of atrazine; 

nevertheless, there are some significant differences between the two that will dictate how and 

when these two herbicides will be used in the production of crops such as com. Overall the 

weed spectrums of these two herbicides are very close; however simazine tends to be a better 

grass herbicide than atrazine. Also, because simazine is relatively Jess soluble than atrazine, 

simazine will remain at or near the surface of the soil where susceptible plants that germinate, or 

have recently germinated, will absorb the chemical. Once simazine is absorbed through the root . 

system it translocates throughout the plant and ultimately affects its control on the whole plant. 

The end result is control of weeds where root absorption takes place. Atrazine is able to move 

vertically through the soil profile quicker than simazine which gives it a broader spectrum of 

weed control. The weed spectrum of atrazine includes large-seeded broadleaf weeds that 

germinate deeper in the soil profile. 

In practical terms, simazine is a good partner herbicide for use with atrazine to control weeds in 

com. Combining these two triazine herbicides as a tank mix results in a system where there is 

control of grasses and broadleaf weeds at the soil surface as well as grass and broadleaf weeds 

1 Registration eligibility decision for simazine. April 06, 2006. 

http://www .epa.gov/oppsrrd I /REDs/simazine_red.pdf 

2 
that germinate lower in the soil profile. However, it is important to remember that these two 

herbicides have the same mechanism of action (MOA) which means that they will need an 

additional herbicide(s) with alternative MOAs to assist in resistance management. Using only 

herbicides with the same mechanism of action will hasten the selection for resistant weed 

biotypes. 

Orange Production 

The production of orange crops is as broad ranging as the geographic regions in which they are 

produced. Oranges are produced commercially in states like Arizona, California, Florida and 

Texas. Because of the way the trees are spaced within an orange grove there is plenty of acreage 

that is not covered by the tree canopy giving weed species a large area to germinate and grow. 

Given the available sunlight, moisture and nutrients these areas of the orange groves are optimal 

places for weeds to thrive. It is for this reason that orange producers utilize herbicides and 

mowing to achieve weed control in their groves. Because of the characteristics discussed in the 

text above, simazine is an important part of the herbicides used in orange production. More than 

a third of the acreage in orange production is treated with simazine at a rate which can be just 

under double the per acre rate of corn. 

COMMON FORMULATIONS AND APPLICATION METHODS 

Simazine is formulated either as a liquid, emulsifiable concentrate, dry flowable or a flowable 

concentrate. It is applied by aerial and ground broadcast, band application, chemigation, and 

spot treatment. 

USE SITES 

Agricultural Use Sites 

Simazine is an herbicide registered for use on caneberries, grapes, strawberries, citrus fruits, nut 

crops, pome fruits, stone fruits, artichokes, com, asparagus, uncultivated agricultural areas, kale, 

cabbage, kohlrabi, brussel sprouts, blueberries, alfalfa, avocado, and olives. 

Non-Agricultural Use Sites 

Simazine is an herbicide registered for use on forest trees, ornamental herbaceous plants, 

ornamental lawns and turf, ornamental woody shrubs and vines, ornamental trees, Christmas tree 

farms, nursery stock, farm buildings, non-agricultural areas, golf course turf, and shelterbelt 

plantings. 

USAGE 

Agricultural Usage 

Figures 1 shows the use of simazine in terms of annual total pounds active ingredient used on all 

crops for the period 1998-2011. During this time period (1998-2011), the annual total 

agricultural usage averaged approximately 6 million pounds a.i. to treat approximately 4 million 

acres for an average application rate of 1.5 lbs. a.i. per acre. The average annual application rate 

for com is 1.1 lb. a.i. per acre, less than the overall average application rate of 1.5 lbs. a.i. per 

acre, while the average annual application rate for oranges is 3.0 lb. a.i. per acre, which is double 

the annual overall application rate. 

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Figure 1. Agricultural Usage Data for Simazine on All Crops in Pounds A.I. (1998-2011) 

8,000.000 

PoundsA.I. 

0 00 C'l C'l C'l C'l C'l .-4 .-4 

0 .-4 N rt') 

0 0 0 0 

0 0 0 0 N N N N 

Source: Proprietary Data, 1998 -2011 

\I\ 1.0 

g g N N 

Years 

4 

" 0 

0 

N 

00 

0 

0 

N 

C'l 0 

0 .-4 

0 0 N N 

.-4 

.-4 

0 

N 
Figure 2 presents the annual total agricultural usage for the more recent 2007-2011 timeframe. 

Usage averaged approximately 5 million pounds active ingredient (a.i.) for 4 million treated 

acres with an overall application rate of 1.25 lbs. a.i. per acre. During this time frame, the crops 

with the highest use in terms of percent of total pounds of active ingredient applied and acres 

treated are corn and oranges (See Table 1). 

On average, the states with the most agricultural usage in terms of percent of total pounds a.i. 

applied are California (22%), Illinois (16%), Florida (15% each), and Indiana (14%) (Proprietary 

Data, 2007-2011). 

Figure 2. Agricultural Usage Data for Simazine Top Crops (2007-2011) 

4,000,000 

Pounds A. I. 

orn 

---Oranges 

Source: Proprietary Data, 2007-201 1 

Table l. Simazine Top Crops in Terms of Percent of Total Pounds Applied, Total Acres 

Treated (TAT), and Average Annual Application Rates in Lbs. a.i. per Acre (2007-2011) 

%Total Acres Treated 

Source: Proprietary Data, 2007-2011 

5 

Average Annual Application 

Rates in Lbs. A.I./ A 
Non-Agricultural Usage 

Non-agricultural usage of simazine is shown in Table 2. Use has fluctuated across all sectors, 

with a noted increase in the institutional and lawn care operator sectors in 2004. This data are 

dated and presented here for reference. 

Table 2. Simazine Select Non-agricultural Use 

Segment/Site 2002/lb. a.i. 

Golf Courses 26,000 

Institutional Turf 12,000 

Landscape N/ A 

Lawn Care Operators (LCOs) 45,000 

Nurseries/Greenhouses 122,000 

TurfFarms 98,000 

N/A: Not Available 

Source: Kline and Company, Inc., 2002, 2004, 2006 

WEED RESISTANCE RELEVANT TO SIMAZINE 

2004/lb. a.i. 

55,000 

329,000 

N/A 

220,000 

177,000 

18,000 

2006/lb. a.i. 

59,000 

10,000 

12,000 

186,000 

13,000 

86,000 

According to The International Survey of Herbicide Resistant Weeds2 there are currently nine 

simazine resistant weed biotypes reported (Table 3), all of which are also resistant to atrazine as 

well. All of these weed biotypes are troublesome in agronomic production, human health, turf 

maintenance and production, as well as maintenance and production of ornamentals. This level 

of resistance could be important in the decision making process for many users when choosing 

herbicides for their herbicide programs. 

Table 3. Weed species with biotYPes resistant to the herbicide active ingredient simazine. • 

Common Name Genus and Species 

1 Annual Bluegrass Poa annua 

2 Barnyardgrass Echinochloa crus-galli 

3 Common Groundsel Senecio vulgaris 

4 Common Ragweed Ambrosia artemisiifolia 

6 Ladysthumb Polygonum persicaria 

7 Lambsquarters Chenopodium album 

8 Smooth Pigweed Amaranthus hybridus 

9 Yellow Foxtail Setaria glauca 

Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. November 15. 2012. 

Available www. weedscience.com 

2 Heap, I. The International Survey of Herbicide Resistant Weeds. Online. Internet. November 15,2012. 

Available www. weedscience.com 

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DATA NEEDS RELEVANT TO BEAD'S FUTURE WORK ON SIMAZINE 

Additional information, in terms of average and maximum percent crop treated, pounds a.i. 

applied, average application rate, regional application, time of application, number of 

applications per year on non-agricultural sites, such as forest trees, farm buildings, ornamentals 

(trees, plants, woody shrubs and vines), from the registrant would improve future assessments of 

the importance of simazine and may be required as part of the registration review of this 

pesticide. 

REFERENCES: 

Proprietary Data, 2000-20 I 0 

Kline and Company, Inc., 2002, 2004, 2006 

USDA, 2006-2010. NASS Crop Reporting Districts. Online: 

http://www.ers.usda.gov/briefing/arms/resourceregions/resourceregions.htm#nass. 

USDA, 2007. Census of Agriculture. Online: http://www.agcensus.usda.gov/Publications/2007/index.asp. 

7 
Appendix 

Agricultural Usage by Crop Reporting District 

Another measure of usage is the use intensity. In this analysis, the use intensity is expressed as 

the pounds a.i. applied per acre of land in farms. This differs from the application rate, which is 

expressed as the pounds a.i. applied per treated area. The average application rate for the period 

2007 to 2011 was 1.25 lbs per acre or 1250 lbs per 1000 treated acres. As shown in Figure 3, 

however, use intensity is 260 lbs per 1000 acres of farm land. Figure 3 spatially represents 

simazine usage by crop reporting district for 2006-2010. The areas depicted in red on the map in 

southern Florida are the citrus growing areas. 

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Figure 3. Simazine Usage by Crop Reporting District (2006-2010) 

Average Pounds Per 

1.000 Acres of Farmland 

- < 11 

- 11- 29 

CJ 30 - 58 

- 59-135 

- 136 - 260 

This is a map of agricultural pesticide usage at the Crop Reporting District (CRD) level prepared by BEAD 

for use in the Environmental Fate and Effects Division documents. These maps are used to help visualize 

where the pesticide being considered is most likely to be used and can be helpful in scenario selection and 

placing the exposure assessment in context. CRDs are boundaries created by USDA NASS which are 

aggregates of counties (USDA, 2010). Pesticide usage is displayed as average pounds (for the years 2006-

2010) per 1,000 acres of farmland in a CRD to normalize for the variation in farmland between CRDs. 

Farmland acreage was obtained from USDA (2007). Farmland or "land in farms" is defined as follows: 

The acreage designated as "land in farms" consists primarily of agricultural land 

used for crops, pasture, or grazing. It also includes woodland and wasteland not 

actually under cultivation or used for pasture or grazing, provided it was part of 

the farm operator's total operation. Large acreages of woodland or wasteland 

held for nonagricultural purposes were deleted from individual reports during 

the edit process. Land in farms includes CRP, WRP, FWP, and CREP acres. 

Land in farms is an operating unit concept and includes land owned and 

operated as well as land rented from others. Land used rent free was reported as 

land rented from others. All grazing land, except land used under government 

permits on a per-head basis, was included as "land in farms" provided it was 

part of a farm or ranch. Land under the exclusive use of a grazing association 

was reported by the grazing association and included as land in farms. All land 

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in American Indian reservations used for growing crops, grazing livestock, or 

the potential of grazing livestock was included as land in farms. Land in 

reservations not reported by reservation, individual American Indians or nonNative Americans was reported in the name of the cooperative group that used 

the land. In many instances, an entire American Indian reservation was reported 

as one farm (2007 Census of Agriculture, USDA). 

Usage is based on private market surveys of pesticide use in agriculture (Proprietary Data, 2006-20 l 0). The 

survey data are limited to the states that represent the top 80-90% of acreage for the individual crops; 

therefore, use may be occurring in regions outside the scope of the survey. CRDs showing no usage of 

pesticides may be due to either the lack of pesticide use in the region or non-participation in the agricultural 

surveys. In addition, across the years, there may be variations in the specific crops included in the CRD 

survey. This may result in a lower annual average for the CRD. 

This map displays ratio data (i.e., average pounds per 1 ,000 acres of farmland) summarized at a very highlevel. Readers are strongly cautioned against trying to over interpret the map without examination of the 

underlying data. The underlying data may explain some of the many reasons that a Crop Reporting District 

may have a high value for a particular active ingredient such as significant acreage (compared with the CRD 

as a whole) of a crop or crops with a high application rate and frequency of application. 

The reader should pay particular attention to the figure legends and realize that a map prepared for a 

particular chemical is not directly comparable to a map prepared for a different chemical. Scale and units of 

measurement do matter and may be different between maps. 

Sources: 

Proprietary Data. 2006-2010 

USDA, 2006-2010. NASS Crop Reporting Districts. 

USDA, 2007. Census of Agriculture. 

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