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February 15, 2016

Petition for Section 18 Emergency Exemption for Tough®

Herbicide (pyridate) for use in mint grown in Wisconsin

A. Summary of General Information

1. Type of Exemption:

Specific

2. Contact Persons:

Steve Salisbury (Technical)

Mint Industry Research Council

PO Box 4059

Salem, OR 97302-1059

Phone: 503-551-3747

Email: steve@pacificagresources.com

Dr. Jed Colquhoun (Scientific)

Department of Horticulture

University of Wisconsin

1575 Linden Drive

Madison, WI 53706

Phone: 608-852-4513

Email: colquhoun@hort.wisc.edu

Julie Braun (Economics)

Wisconsin Mint Board

PO Box 327

Antigo, WI 54409

Phone: 715-623-7683

Email: jbraun@wisconsinpotatoes.com

Liesbeth Bosman (Registrant)

Belchim Crop Potection, Inc.

Technologielaan 7

1840 Londerzeel

Belgium

Phone: +32 (0) 473 86 52 33

Email: Liesbeth.Bosman@Belchim.com
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3. Description of Pesticide

Active Ingredient: Pyridate

Trade Name: Tough Herbicide 5EC, not currently registered in U.S. 

Formulation: Emulsifiable concentrate formulated at 55.8% (5.0 lb. ai. per gal.) and 44.2 

% inert ingredients.

Registrant/Manufacturer: Belchim Crop Protection a Belgium based company (EPA 

Company No. 91746). The U.S. distributor is Engage Agro USA Corp. Material Safety 

Data Sheet (MSDS) and labels are attached.

4. Description of Proposed Use

a. Sites to be Treated 

There are approximately 3,500 acres of mint grown in Wisconsin. It is estimated that 

approximately 3,100 (90%) of this acreage will need to be treated with Tough. The mint 

production areas are located in Wisconsin counties of Adams, Columbia, Dane, Dodge, 

Green Lake, Jefferson, Marquette, Oconto, Rock, Sauk, and Walworth. The soils of these 

mint growing counties are generally productive, deep, and fertile in agricultural areas 

where a diversity of crops are also grown. 

 

b. Method of Application

The herbicide will be applied by ground-driven spray equipment and applied by licensed 

applicators in accordance with the EPA approved label. Tough will not be applied by 

aerial methods or through any type of irrigation system.

c. Rate of Application

A maximum of 0.9375 lb. active ingredient per acre (24 ounces of product per acre) in 

20-40 gallons of water per acre will be applied during the growing season.

d. Maximum Number of Applications

Two applications of Tough per growing season may be made, if necessary, with a 

minimum of 14 days between applications. Applications may be made between the dates 

of April 1 and December 31, 2016. No applications will be made within 49 days of 

harvest.

e. Total Acreage to be Treated

It is estimated that approximately 3,100 acres (90% of total Wisconsin acreage) will need 

to be treated with Tough.

f. Total pesticide to be used 

An estimated 1,163 gallons (5,815 lbs of a.i.) of herbicide are expected to be applied. 

3,100acre * 24 fl.oz. * 2 applications = 1,163 gal. of formulated product. 

1,163 gal * 5 lb a.i./ gal = 5,815 lbs of active ingredient.
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g. Use season 

We are requesting application beginning April 1 through December 31, 2016. A fall 

application after harvest may be necessary if conditions promoting weed growth occur. 

No applications will be made within 49 days of harvest.

h. Harvest Dates

The majority of peppermint acreage is harvested once in August. However, some 

peppermint growers are double cutting their crop. Double-cut mint is harvested twice 

during the growing year, once in June and again in late August or early September. 

Spearmint is harvested twice during the growing season, once in the middle of June and 

again in the middle of August. 

i. Other Restrictions, User Precautions, and Requirements

Federal and supplemental labels address reentry and worker protection, environmental 

hazards and restrictions (see attached label). Treated fields or forage from treated fields 

may not be used for livestock feed or grazing. Tough will not be applied through any type 

of irrigation system or by air. To protect endangered freshwater invertebrate species, 

Tough will not be applied within 100 yards of any freshwater spring.

5. Alternative Methods of Control

a. Registered Post-Emergent Herbicide Alternatives

1. Bentazon (Basagran) – Provides inconsistent (partial) post-emergence control of 

Kochia. Does not control pigweed. Weeds emerging after application are not 

controlled.

2. Bromoxynil (Maestro) – Phytotoxic to actively growing mint. Cannot be applied 

above 70 degrees F to actively growing mint. Only gives partial control of Kochia 

and Pigweed seedlings. Kochia and Pigweed seeds germinate (multiple flushes) 

throughout the growing season.

3. Clethodim (Select Max) – Grass weed control only.

4. Clopryalid (Stinger) – For spot treatment, post emergence control of broadleaf weeds 

(canada thistle, dandelion). Destroys mint which comes in contact with herbicide. 

Does not control Kochia or Pigweed

5. MCPB (Thistrol) – Can only be applied early post-emergent to weeds and to 

dormant or small/newly emerged mint. It is limited to partial control of Canada 

thistle and field bindweed. Does cause crop injury and loss of oil yield. 

6. Quizalifop (Assure II) – Grass weed control only.

7. Sethoxydim (Poast Plus) – Grass weed control only.
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8. Terbacil (Sinbar) – Does not control Kochia. Pigweed has developed resistant 

biotypes due to years of continuous use. It is not effective on weeds that have grown 

beyond the seedling stage. Cannot be used when rotating from mint into other crops 

the following year due to soil persistence and crop rotational restriction. Cannot be 

used on sandy, loamy sands, or soils with less than 1% organic matter without crop 

injury.

b. Other alternatives

Mechanical weed control methods such as tillage are not feasible or practiced in actively 

growing mint due to the destruction of the crop. Tillage in mint at any time also spreads 

the disease Verticillium Wilt, a fungal pathogen in mint which is spread by the movement 

of soil and debris. Tillage also spreads the rhizomes and stolons of perennial weeds. Hand 

rogueing is cost prohibitive and does not provide season long control of weeds as weed 

seeds continue to germinate in the soil throughout growing season. In addition, the labor 

needed for hand weeding is not available in most mint growing regions. Crop rotation is 

practiced when feasible, but mint being a perennial crop is left in production for 3 to 5 

years, or longer. Research on biological control methods is currently being conducted, but 

as of to date no effective methods have been developed. 

c. On-going research for chemical alternatives

The mint industry has placed a high priority on finding alternatives to pyridate for 

postemergence broadleaf weed control. The industry has diligently invested several 

hundred thousands of dollars of research funds for the past decade to this effort. Numerous 

preemergence and postemergence herbicides have been tested and evaluated with little or 

no success. Preemergence herbicides evaluated include pendamethalin, terbacil, 

saflufenacil, sulfentrazone, flumioxazin, oxyfluorfen, pyroxasulfone and both oxyfluorfen 

and flumioxazin impregnated on fertilizer have been tested. Postemergence herbicides that 

have been tested include bentazon, terbacil, bromoxynil, bicyclopyrone, mesotrione, 

tembotrione, topramezone, fluroxypyr, MCPB, and carfentrazone. These herbicides are 

either too injurious to the mint or do not adequately control the pigweed. A letter from Dr. 

Rick Boydston, USDA-ARS, is attached summarizing mint herbicide research since 2006.

In summary, despite extensive efforts the mint industry has not been able to successfully 

find an adequate replacement for pyridate (Tough herbicide) to provide postemergence 

weed control that does not cause significant injury to the mint crop. Therefore, weed 

control remains an urgent situation challenging the ability to produce high quality mint oil. 

In addition to the urgency of the situation, it is important to note that postemergence 

broadleaf weed control has recently developed into an un-routine situation due to the 

increased demand for double-cut production acreage. Many acres have been forced to 

double-cut production to meet recent global regulatory and market demands. Further 

description of this un-routine situation is discussed in Section B Part 2 (Description of the 

Emergency Condition) of this request. 
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6. Efficacy of the Proposed Use

Results of efficacy and comparative field trials are attached. Tough selectively controls 

annual weeds in mint without causing significant crop injury. Risks to rotational crops are 

minimized due to the short half-life and low soil persistence leading to no residual impact to 

subsequent crops. Tough is the only known broadleaf herbicide that can provide post-emergent 

control of weeds without impacting crop yield. 

Since there is a limited amount of trial data from Wisconsin, a letter of support from Dr. 

Jed Colquhoun, University of Wisconsin, is attached explaining the benefits and usability of 

Tough in mint production.

7. Residue Information

 Residue trials for mint were conducted by the IR-4 Program in 1994. Applications made in 

accordance with the requested provisions are not expected to result in residues of pyridate and its 

metabolites in excess of 0.2 ppm for peppermint and spearmint tops. These tolerances have been 

established by the EPA and are recorded under CFR 180.462. Secondary residues in meat, 

poultry, and eggs are not expected to result.

8. Risk Information

 On May 3, 2000 the EPA established tolerances of 0.2 ppm for residues of pyridate and its 

metabolites in/on peppermint and spearmint tops. Information regarding pyridate toxicology and 

aggregate exposure can be found in the final rule published in the Federal Register May 3, 2000, 

volume 65, number 86, pages 25647-25652 (attached).

a. Human Health

Tough herbicide poses little potential risks to humans, domestic animals, wildlife, and the 

environment. The acute oral LD50 for male rats is > 5,000 mg/kg. The active ingredient 

has a low dermal irritation potential and a low inhalation hazard. Acute dermal LD50 for 

rabbits is > 2,000 mg/kg. Inhalation LC50 >4.37 mg./L air. Primary dermal irritation 

study indicated it is mildly irritating to rabbit skin (EPA Health Effects Division of the 

Office of Pesticide Programs, 2000).

The EPA concluded that residues of pyridate in drinking water do not contribute 

significantly to the aggregate acute human health risk. The acute human health risks 

resulting from exposure to pyridate in food and water are below EPA’s level of concern 

for all population subgroups. As for chronic risk, the EPA also concluded that no harm 

will result from aggregate chronic exposure.

It was also determined that pyridate is not carcinogenic in either rat or mouse, and 

therefore is not expected to pose a cancer risk to humans.

The product label addresses the risks to worker/applicator by outlining handler 

precautions and required personal protective equipment.
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b. Potential to be found in drinking water

The potential for exposure to residues of pyridate in drinking water is negligible due to its 

low water solubility (1.5mg/L at 20 C), strong soil adsorption (Kd = 0.3-26) and short 

half-life (7-21 days). Pyridate is essentially immobile in all soil types and any risks to 

surface or groundwater contamination will be negligible. 

The EPA Health Effects Division determined that pyridate does not possess the 

environmental fate parameters associated with a compound that could leach to 

groundwater. However, the parameters of its degradate indicate that under unusual 

conditions such as flooding, where anaerobic conditions persist in topsoil for up to 60 

days, the degradate could possibly leach to groundwater or run off to surface water. 

Pyridate is not listed in the EPA Pesticides in Ground Water Database, nor is there an 

EPA Maximum Containment Level or health advisory. 

c. Residential Uses

Pyridate is not registered for use in ornamentals or in residential areas.

 

d. Common Mode of Action

Pyridate is a Group 6 herbicide, HRAC Group C3 (Herbicide Resistance Action 

Committee, www.hracglobal.com). It belongs to the phenyl-pyridazine family of 

herbicides. Its site of action is inhibition photosynthesis by blocking electron transport in 

photosystem II (reactions taking place in the chloroplast thylakoid membranes). 

 

e. Endangered or Threatened Species

Endangered or threatened species listed by the USFWS within the mint production 

counties of Adams, Columbia, Dane, Dodge, Green Lake, Jefferson, Marquette, Oconto, 

Rock, Sauk, and Walworth are listed in the attached table. 

The use of Tough herbicide in accordance to the label in mint fields should not pose a 

risk to any threatened or endangered species. 

 

f. Beneficial Organisms

Tough is not toxic to bees and other beneficial insects (i.e. lady beetles, predatory mites). 

See the attached EPA Environmental Fate and Effects Division (EFED) report. 

g. Fish and Aquatic Organisms

Pryridate is considered toxic to estuarine organisms. However, due to its strong soil 

adsorption and short half-life, if applied according to the label it should not pose a risk to

estuarine organisms (see attached EPA EFED report). The label states that this material 

should not be applied within 100 yards of any freshwater spring, directly to water, to 

areas where surface water is present, or to intertidal areas below the mean high water 

mark.
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9. Coordinate with Other Agencies

The Wisconsin Fish and Game Office of the U.S. Fish and Wildlife Service will receive a 

copy of this request. Any comments received will be forwarded to the U.S. EPA.

10. Notification of Registrant

Belchim Crop Protection has been notified and their letter of support is attached. In 

addition, Engage Agro USA Corp. is the U.S. distributor and they have also been notified. A 

letter of support from Engage Agro USA is also attached.

11. Enforcement Program

The Wisconsin Department of Agriculture, Trade and Consumer Protection (WDATCP)

has adequate authorities for enforcing provisions of Section 18 emergency exemptions. 

WDATCP will require the registrant (or manufacturer, if unregistered) of Tough herbicide, 

Belchim Crop Protection, to prepare and make available to end users supplemental labeling that 

complies with WDATCP and EPA requirements for the emergency use, if approved. Applicators 

will be required to keep adequate records of application use and acreage. The Mint Industry 

Research Council (MIRC), in cooperation with Belchim Crop Protection and Engage Agro USA, 

will be required to provide the WDATCP a report summarizing results of the emergency use 

after the end of the use period. 

12. Repeat Uses

Tough has been previously used under a Section 18 from 1999-2000. Tough was later 

registered under an SLN 24c from 2001-2007 after tolerances were established in 2000.

13. Progress Toward Registration

 Registration and tolerance were established through the IR-4 by the EPA in May of 2000. 

The Final Rule was published in the Federal Register vol. 65, No. 86, May 3, 2000 pages 25647-

25652 (attached). Tolerances were established for peppermint and spearmint tops at 0.20 ppm 

(CFR 180.462). Product registration was voluntarily cancelled by the registrant (Syngenta) and 

the product was no longer marketed in the U.S. Recently, Belchim Crop Protection acquired the 

marketing rights for pyridate from Syngenta. It is understood that Belchim is working with the 

EPA to re-register Tough in the U.S.

B. Summary of Economic Loss

1. Pest(s) to be Controlled

The pests causing an emergency are broadleaf weeds, in particularly Redroot Pigweed, 

Armaranthus retroflexus and Kochia, Kochia scoparia.

2. Discussion of the Emergency Condition

This request is due to the emergency condition existing in mint from the postemergence 

of pigweed, kochia, and other broadleaf weed communities that cannot be effectively controlled 

in active growing mint crops. All crops including mint suffer yield losses from populations of 

weeds, but unlike other crops, the quality of mint oil also is affected by weeds. A quality 

marketable mint crop is dependent upon weed free fields. 
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The recent increase in global demand for the production of double-cut mint oil has 

created an un-routine situation that poses additional stress on the need for adequate 

postemergence broadleaf weed control. Preemergence herbicides applied in February/early 

March to dormant mint dissipate to low levels that no longer control weeds after 4-6 weeks. The 

mint crop canopy suppresses any new weed emergence or establishment after this period. Once 

the mint canopy is removed with a mid to late June harvest (first cutting), new weed flushes 

follow. These new flushes include both summer annual grasses and later germinating broadleaf 

weeds such as pigweeds. The grass weeds are easily controlled with registered grass active 

herbicides. However, there are no effective postemergence herbicides that are labeled in mint for 

pigweed control during the second half of the growing season following the first harvest of mint. 

The increased demand for double-cut mint is a result of both global regulatory challenges 

and the increasing desire for the oil quality that is produced in double-cut production. The global 

regulatory issues involve the concern of menthofuran and pulegone contents in the mint oil and 

the limits of these compounds that are allowable in oil to deem it acceptable in markets. The 

reduction of these compounds and the increase of other desirable oil quality traits can be 

achieved through double-cut production. The market has shifted to a higher demand for doublecut mint, but the acreage to meet the demand is not adequate due to management challenges 

associated with double-cut production. Postemergence broadleaf weed control is the primary 

management challenge facing double-cut production. Producers do not have viable broadleaf 

weed control options to address this challenge. 

Redroot pigweed present in mint at 1.6 weeds/yd2renders mint oil unmarketable, due to 

off-flavors imparted during the distillation process (attachment). OSU research also 

demonstrated that a redroot pigweed infestation of 10 plants/ft2caused a peppermint oil yield 

reduction 34.4 lbs/acre, a 46% reduction (attached). Furthermore, both redroot and prostrate (A. 

blitoides) pigweeds have developed terbacil resistant biotypes. 

Kochia, a summer annual, can reach heights of six feet high and several feet in diameter, 

hindering harvest operations and competes for nutrients and light. In addition, an infestation of 

2.3 kochia plants/ft2can reduce mint oil yields by over 30% (attachment) in addition to reducing 

oil quality.

Mechanical tillage is not a post emergence weed control option in mint because tillage 

will destroy growing mint, eliminate irrigation rills in surface irrigated fields, and will spread 

devastating diseases in mint such as Verticillium wilt (Verticillium dahliae). Terbacil (Sinbar), 

the commonly used herbicide registered for weed control in mint, is weak on pigweed species 

and has become even less effective in controlling pigweeds due to the development of resistant 

biotypes. Additionally, terbacil cannot be used when weeds are beyond the seedling stage and 

when rotating from mint to other crops due to residual carryover. The only alternative method of 

controlling these weeds is hand-rogueing, but the unavailability of labor and excessive cost 

where labor is available, eliminates rogueing as a viable weed control method. Again, there are 

presently no effective post-emergent means of controlling these weeds in mint. 

The mint industry has been diligently investing research funds to discover effective postemergent broadleaf weed herbicides that are safe to the crop. Pyridate has proven to be effective 

on broadleaf weeds as well as possesses acceptable post-emergence crop safety needed for mint 

production. Populations of problem weeds have reached economically devastating levels and is 

impacting the producer’s ability to compete in the market. Additionally, the recent increased 

demand for double-cut mint has forced production into and created an un-routine situation for 
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mint producers who have no effective and viable postemergence broadleaf weed control options. 

The use of Tough herbicide for postemergence weed control in mint is critical to maintaining 

U.S. mint oil quality and market share in today’s global economy. 

3. Discussion of Economic Loss

Redroot Pigweed/Kochia and broadleaf weed communities have become serious weed 

pests of mint growers in Wisconsin. The lack of any post emergent weed control option, (no 

effective registered herbicide, and the presence of herbicide resistant pigweed) have created an 

emergency situation for Wisconsin mint growers. Furthermore, the recently increased demand 

for double-cut mint has created an un-routine situation in weed control for mint producers. 

Economic thresholds for these problem weeds are very low. Weeds resistant to herbicides which 

mature and form seeds, soon establish large populations of the resistant biotype, if not controlled. 

Studies performed by OSU weed scientists show yield losses ranging from 22%to 47% 

from the target weeds individually (attachment). Kochia and Redroot Pigweed are often found in 

complexes of other weeds, which further reduces the yield and quality of mint oil.

Five-Year History of Wisconsin Production

Year

Average 

Yield 

Average 

Price

Gross 

Revenue

Cost of 

Production

Net 

Revenue

(lbs / acre) ($ / lb) ($ / acre) ($ / acre) ($ / acre)

2011 71 $21 $1,497 $1,100 $397 

2012 55 $21 $1,159 $1,100 $59 

2013 54 $21 $1,139 $1,100 $39 

2014 48 $21 $1,007 $1,100 ($93)

2015 57 $21 $1,196 $1,100 $96 

Average 57 $21 $1,200 $1,100 $100 

1. Yield and price data were obtained from mint industry oil growers and buyers.

2. Cost of production is based on local industry knowledge. 

3. A loss does not necessarily mean a negative cash flow, but rather that the grower will not earn a 

return on capital and management contributions (hourly wage, labor, etc) equal to what could be 

earned in an alternative investment of the land producing the mint crop.

Tier 2 Analysis

A Tier 2 Significant Economic Loss (SEL) analysis illustrates the reduction of oil yield 

and quality as well as the loss of gross revenue due to the devaluation of tainted oil resulting 

from weed contaminants. The yield comparison reflects a 35% yield reduction (OSU trial data) 

on the portion of the acres (90%) faced with the impact of post-emergent weed control 

challenges. 
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Furthermore, the yield calculations are based on the five-year average (2011-15) of 57

lbs/acre. As previously stated in this request, the estimated acreage of Wisconsin mint is 3,500 

acres and approximately 3,100 acres (90%) would be treated with Tough herbicide.

As for marketable oil quality, it is estimated that the use of Tough herbicide would 

increase pure quality oil by 20%, thus reducing the amount of tainted devalued oil by the same. 

The devaluation of tainted oil ranges from a small percentage deduction to complete 

rejection/loss. Based on industry knowledge, an average devaluation of 35% was used for this 

analysis.

The Emergency situation results in 20% more tainted oil that has 35% less value realized 

by the growers. In all, this is a gross revenue loss greater than $2Million to the mint producers in 

Wisconsin.

Tier 2 Wisconsin Economic Analysis of Yield and Quality Loss

Baseline Emergency Change % Change

Yield (lbs/acre) 296,181 199,500 -96,681 -33%

Pure (% of yield) 90% 70%

(lbs/acre) 266,563 139,650 -126,913 -48%

Tainted (% of yield) 10% 30%

(lbs/acre) 29,618 59,850 30,232 102%

Price, Pure ($/lb) $21.00 $21.00

Price, Tainted ($/lb) $13.65 $13.65

Gross Revenue ($/acre) $6,002,103 $3,749,603 -$2,252,501 -38%
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C. Supporting Documentation

1. Tough 5EC Package Label. 

2. Tough 5EC Section 18 Supplemental Label. 

3. Tough 5EC MSDS. 

4. Tolerance of Peppermint to Pyridate. Oregon State University Efficacy Data. Hyslop 

Farm, Corvallis, OR. 1993.

5. Efficacy and Crop Safety Data 1994, 1995. Binning, L.K., et.al. University of Wisconsin.

6. Letter of Support. Dr. Jed Colquhoun, University of Wisconsin. Madison, WI.

7. Federal Register. Vol. 65, No. 86. Wednesday, May 3, 2000. pp. 25647-25652.

8. EPA Health Effects Division Risk Assessment. Pyridate (i.e. Tough®) in/or on Brassica 

Head and Stem Subgroup, Collards and Mint. January 24, 2000.

9. Endangered/Threatened Species Found in Wisconsin Mint Producing Counties. February 

2016. http://ecos.fws.gov/tess_public/

10. EPA Environmental Fate and Effects Division – Pyridate Report. December 12, 1989.

11. Belchim Crop Protection N.V./S.A. Letter of Support. January 13, 2016.

12. Engage Agro USA, LLC. Letter of Support. February 4, 2016.

13. The Effect of Weeds on Mint Oil Yield and Quality. Heap, I. Department of Crop and 

Soil Science. Oregon State University. 

14. Herbicide Resistant Weeds in Mint. Heap, I. WeedSmart, Corvallis, OR.

15. Terbacil and Bromacil Cross-Resistance in Powell Amaranth (Amaranths powellii). 

Boydston, R and Al-Khatib, K. Weed Science. Volume 40:513-516. 1992.

16. Pyridate Properties and Characteristics. Heap, I. pp. 89-91.

17. Letter summarizing weed research efforts searching for alternatives to pyridate. Dr. Rick 

Boydston. USDA-ARS. Prosser, WA. March 1, 2016.