UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

AUG 192015 

OFFICE OF CHEMICAL SAFETY 

ANO POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

BEAD Chemical Profile (BCP) for Registration Review: Endothall (Case 2245 

PC Codes: 038901-038908) 

Carl Chen, Biologist 

Biological Analysis Branch ~~ 

Claire Paisley-Jones, Biologist L ~s lvvi" L 

Science Information and Analysis Branch / "-~/ 

Derek Berwald, Economist 

Economic Analysis Branch 

Biological and Economic Anal 

Arnet Jones, Chief 

Biological Analysis Bran 

Diann Sims, Chief /{J}-<.AA.._.(xμ-,rV'._.,.. .... 

~~~ 

Science Information and Analysis Branch 

T

Economic 

imothy Kiely

Anal, ys

Chi

is 

ef 

Branch ~ V\Jl ~ Biological and Economic Analy ·s Division ( ..., ) 

Garland Waleko, Chemical Review Manager 

Pesticide Re-evaluation Division (7508P) 

Peer Review Panel date: April 29, 2014 
SUMMARY 

Endothall is primarily used as an aquatic herbicide and biocide, but it is also registered as a 

harvest aid for crops like cotton, alfalfa seed and clover seed. BEAD has little information on 

the non-agricultural uses of endothall, even though the amount of use in aquatic environments 

may be far higher than the amount used on agricultural crops. 

INTRODUCTION 

The Biological and Economic Analysis Division (BEAD) Chemical Profile (BCP) provides an 

overview of the pest management roles and quantitative usage information for endothall. The 

BCP includes summaries of previous BEAD products and available public and/or private use and 

usage data for Endothall to describe the role of this chemical in pest management. Additional 

information on use is available in the Endothall Label Data Report. Information provided in this 

BCP may be used by stakeholders (e.g., users and registrants), OPP risk assessors, and OPP risk 

managers, and the general public during the Registration Review process of this pesticide. 

HISTORY OF ENDOTHALL AND BEAD PRODUCTS 

Endothall is registered as an aquatic herbicide, desiccant, and biocide. There are currently three 

active ingredients with end-use products associated with this case: endothall acid (03890 I), 

endothall-dipotassium (038904), and endothall mono salt (038905). Endothall acid (038901) is 

registered exclusively for use on cotton. Endothall-dipotassium (038904) is registered 

exclusively for aquatic use. Endothall mono salt (038905) is registered for use on alfalfa and 

clover grown for seed, potatoes, and for aquatic use. Hereafter, the term endothall refers to all 

three active ingredients in this case, unless otherwise specified. A Registration Eligibility 

Decision (RED) for endothall was published by EPA in 2005. 

BEAD has issued several documents on endothall since the RED was published. There were two 

reviews of Section 18 Emergency Exemption requests for the use of endothall to control weeds 

in irrigation canals without a holding time restriction. Endothall was requested by a canal 

company in Idaho after other control methods were determined to be too dangerous to company 

staff. BEAD concluded that this was an urgent situation where the canal company did not have 

safe alternative control methods available (EPA 2008), and thus a Section 18 was issued. 

Another Section 18 request was made by the Nebraska Department of Agriculture. BEAD's 

review (EPA 2009) concluded that' there was not enough information to evaluate the request, so 

no Section 18 was issued. 

2 
USE SITES 

Agricultural Use Sites 

Endothall is registered as a desiccant for use on alfalfa and clover grown for seed, cotton, and 

potatoes. 

Non-Agricultural Use Sites 

Endothall is registered for use in lakes, ponds, and irrigation canals to controls algae and 

submerged aquatic vegetati<?n, and to control mollusks and algae in commercial/industrial water 

cooling systems. 

FORMULATIONS 

Endothall is formulated as granular and soluble concentrate. 

APPLICATION METHODS 

Endothall is applied to terrestrial sites as a broadcast application with air or ground equipment. 

For aquatic applications, endothall is applied by metering device, drip feed, injection, sprayer, or 

granule applicator. 

3 
USAGE 

Agricultural Usage 

70,000 

Pounds Al 

I co en 0 en en 0 en en 0 ..... ..... N I 

..... 

I 

N ,..., ~ U'I \D r-.. co en 0 ..... 0 0 0 0 0 0 0 0 0 ..... ..... 0 0 0 0 0 0 0 0 0 0 0 N N N N N N N N N N N 

- Pounds Al - Total Area Treated 

N ,..., ..... ..... 0 0 N N 

210,000 

Total Area 

Treated 

Figure 1. Endothall Total Acres Treated & Total Pounds A.I. Applied (1998-2013). 

Source: Proprietary Data, 1998-2013 

Agricultural usage of endothall was at one point quite high, with almost 210,000 acres treated in 

l 998. During the last five years, however, agricultural usage of endothall has been very low 

(Figure I). From, 2004-2008, approximately 4,500 pounds of endothall were applied annually. 

During this period, the majority of endothall used on agricultural crops was applied to potatoes, 

with the remaining 30% being applied to cotton (Table l ). From 2009 - 2013, no usage was 

recorded for potatoes and only a small amount was applied to cotton. 

Table 1. Comparison of Crops with Highest Use of Endothall - Percent of Total 

Pounds of A.I. A lied between i004-2008 and 2009-2013. 

2004-2008 

Av e Annual = · 4,500 lbs 

Cro 

Cotton 

% of Total Pounds 

A lied 

30 

Potatoes 70 

Source: Proprietary Data, 2004-2013 

Cro 

Cotton 

2009-2013 

e Annual = I 50 lbs 

% of Total Pounds 

A lied 

100 

The only remaining agricultural crop with recorded endothall usage is cotton. Approximately 

150 lbs per year of endothall were applied to over 4,000 acres of cotton at an average rate of 0.04 

lbs A.I per acre between 2009 and 2013 (Table 2). 

4 
Crop 

Cotton 

*Total Acres Treated sums all acres treated for a crop, including those acres that receive multiple treatments. 

Source: Proprietary Data, 2009-2013 

Along with the decrease in total usage the number of states with recorded endothall usage also 

greatly decreased, from 16 between 2004 and 2008, to just two between 2009 and 2013 (Table 

3). This pattern reflects the end of usage in potato production, as well as a decrease in usage on 

cotton. 

Table 3. Comparison of States with Highest Use of Endothall - Percent of Total 

P oun d s A I A .. .pp I" 1e db e tw een 2004 -2008 an d 2009 -2013 . 2()();b2008 " 2009-2013 - -

Avera2e Annual = 4,500 lbs A verasze Annual = ISO lbs 

State % of Total Pounds State ~ % oJTotal Pounds 

Aoolied Annlled 

Colorado 40 Texas 55 

North Dakota 20 California 45 

Wisconsin 10 

Arizona 10 

Texas 5 

California 5 

Other* 10 , 

*Other states: ME, LA, OK, MS, AL, SC, PA, NY, TN, MO 

Source: Proprietary Data, 2003-2012 

No usage data are available on endothall usage on alfalfa and clover seed crops. 

Non-Agricultural Usage 

In nonagricultural settings, endothall is used in lakes, ponds, and irrigation canals to control 

algae and submerged aquatic vegetation, and to control mollusks and algae in 

commercial/industrial water cooling systems. The only data available data on endothall usage in 

these sectors describes usage in golf course ponds to control the growth of aquatic plants. In 

2011 , approximately 3,000 pounds of endothall were applied to golf course ponds, accounting 

for less than 2 percent of total aquatic herbicide usage and making it the fifth most commonly 

used aquatic pesticide in this sector (Table 4). 

5 
Table 4. Endothall use as an a 

Secto"F 

2011 

Golf Course Ponds 3,000 

Source: Proprietary Data 2006, 2011 

While no usage data are available on other aquatic uses of endothall, these other aquatic uses 

have the potential to be large. 

CHEMICAL AND USE CHARACTERISTICS 

The endothall acid that results in pesticidal activity is fom1ed as a breakdown product from 

application of its salt forms. Endothall is a contact herbicide and algicide. It can also function as 

a plant growth regulator to defoliate plants, and a biocide to control invasive organisms such as 

mollusk. Endothall' s mode of action has not been classified by the Herbicide Resistance Action 

Committee (HRAC) or the Weed Science Society of America (WSSA) (HRAC, 2015; WSSA, 

2015). 

ROLE OF ENDOTHALL IN PEST MANAGEMENT 

Endothall is mainly used as an aquatic herbicide and algicide. It is registered to control aquatic 

weeds such as algae and submerged aquatic plants in ponds, lakes, and other water bodies under 

Section 3 of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). In Florida, the 

estimated aquatic usage of endothall for the period of 2004-2005 is approximately 220,000 

pounds of active ingredient (Mossi.er and Langeland, 2006). Thus, the aquatic use in Florida 

alone dwarfs the agricultural uses nationwide. Multiple Section 2(ee) recommendations have 

also been issued for use of endothall in 48 states to control aquatic plants including 

approximately 10 specific pondweed species (CDMS, 2015). 

Endothall and its salts are registered for use on cotton, potatoes, and seed crops of alfalfa and 

clover. One endothall end-use product, Des-i-cate, played a role as a harvest aid or a vine killer 

on potato crops but was cancelled in 2005. One endothall mono salt end-use product, Desicate II, 

is still registered for use on potatoes, however, no usage has been recorded in the past five years 

(Proprietary Data 2009-2013). As mentioned above, the data show current agricultural use of 

endothall only on cotton at a low level (Proprietary Data, 2009-2013). 

6 
DATA NEEDS 

The Agency currently does not have complete information on endothall. Obtaining the following 

information may improve future assessments conducted by the Agency related to the use and 

importance of endothall. 

Agricultural Use 

• Endothall usage data for alfalfa and clover seed crops, such as amount 

applied, application timing and area treated . 

• Any information on the importance of endothall compared to alternatives 

for cotton production. 

Non Agricultural Use 

• EPA has little information on how much and how endothall is used for 

aquatic weed control. Usage data on aquatic uses of endothall, such as 

type of water body treated, amount applied, and the area treated would be 

very helpful. 

7 
REFERENCES 

BEAD. 2014. Endothall Screening Level Usage Analysis. Biological and Economic 

Analysis Division, Office of Pesticide Programs, US Environmental Protection Agency. 

CDMS. 2015. Crop Data Management Systems (CDMS) Label Search. CDMS, Inc. Accessed 

March 2015 at https://premier.cdms.net/webapls/FormsLogin.asp?/webapls/. \ 

EPA. 2005. Registration Eligibility Decision Endothall. Prevention Pesticides and Toxic 

Substances, US Environmental Protection Agency. 

http://www.epa.gov I oppOOOO 1 /reregistration/REDs/ endothall _red. pdf 

EPA. Pesticide Chemical Search Ehdothall. Online: 

http://iaspub.epa.gov/apex/pesticides/f?p=CHEMICALSEARCH:21 :0: :N0:2 l :P21 _NA 

ME VAL:\ENDOTHALL%20AND%20SALTS%20REREGISTRA TION%20CASE\ 

HRAC. 2015. Classification of Herbicides According to Site of Action. Herbicide Resistance 

Action Committee (HRAC). Accessed March 2015 at 

http://hracglobal.com/pages/classificationofherbicidesiteofaction.aspx 

Kline and Company, Inc., 2006, 2011 

Mossier MA, Langeland KA. 2006. Florida Crop/Pest Management Profile: Aquatic Weeds. PI138 of Pesticide Information Office. Florida Cooperative Extension service. University of 

Florida. Accessed April 2015 at https://edis.ifas.ufl.edu/pil 75 . 

Proprietary Data. 1998-2013. (pesticide usage data) 

WSSA, 2015. Classification of Herbicides According to Site of Action. Weed Science Society of 

America. Accessed March 2015 at 

http://weedscience.org/documents/showdocuments.aspx?OocumentID= I 193. 

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