Information Requests Monitoring System

This data is maintained as an archive.

Request ID: 91
Request From: Steve Toth
Date Requested: Sep 28, 2004
Request: USDA's Office of Pest Management Policy is requesting information on chlorsulfuron. Please forward the following information to those in your state and/or territory that can respond and forward the responses to us. Thanks. Steve Toth --------------------------------------------------------------- Dear Colleagues: EPA has published the preliminary risk assessment for chlorsulfuron. EPA has identified potential risks to endangered plants through direct and indirect sprays of chlorsulfuron. Following is the link to EPA's eDOCKET. The closing date for comments is November 23.;jsessionid= 1924BC81C9002CB276E095BD03A6D8D5?objectId=0b0007d48031a818 EPA has requested that we provide them with the benefits of chlorsulfuron. Could you please request feedback from your organizations in this regard? In the next week or so I will contact you as to next steps. We will try to arrange a briefing between DuPont and stakeholders in the next several weeks as to their plans for chlorsulfuron. There will probably be a briefing later with EPA regarding the risk assessment for the benefit of those who wish to submit written comments to EPA. Please copy me on any submitted comments and your benefits information for chlorsulfuron so we can consider your interests as we interact with EPA on the reregistration of this chemical. Your comments on the feasibility of EPA's proposed risk mitigations are also needed. Please forward this e-mail to other stakeholders who might be interested. This e-mail is sent ahead so that you may begin your own analysis ahead of the briefings, time permitting. Teung ============================================================== Following are excerpts from the "Overview of Chlorsulfuron Risk Assessment." Use Profile Based on available usage information for the years 1988 through 1999, the Agency estimates that chlorsulfuron usage averaged approximately 72,000 pounds of active ingredient per year to treat over 5.5 million acres. Its largest markets in terms of total pounds active ingredient are winter wheat (90%) and spring wheat (5%). The remaining usage is primarily on barley, oats, fallow fields and pasture/hay. Crops with a high percentage of the total U. S. planted acres treated include winter wheat (11%) and oats (2%), while registered sites with little or no usage include lawn and ornamental turf. Most chlorsulfuron usage is in California, Idaho, Kansas, Minnesota, North Dakota, Oklahoma, Oregon, South Dakota, Texas, and Washington. Data are not yet available for the new use on pastures and rangelands that EPA approved in 2002; however, chlorsulfuron is reportedly used in these areas by the US Department of Interior (Bureau of Land Management) to control invasive weed species. Non-Target Plant Risk * EPA is concerned about the risk to non-target plants from both drift and exposure to contaminated water. * Chlorsulfuron can harm plants when absorbed by roots or foliage. Chlorsulfuron exposure may cause visible effects, such as death, in days or weeks; or it may cause delayed effects on fruit and seed production observable several weeks or months after exposure. Symptoms vary, depending on the sensitivity of the plant and the magnitude of exposure. * Vegetative vigor and seedling emergence studies were used to screen risks for non-target and endangered plants. - Repeated vegetative vigor studies have recently been submitted to the Agency because the earlier studies did not establish a NOAEL. These studies will be reviewed and considered before the Agency makes a decision regarding chlorsulfuron's eligibility for reregistration. Risks to Non-target Plants from Drift and Run-off * Some researchers have concluded that small quantities of chlorsulfuron, such as might be found in airborne particles traveling long distances, may affect plant reproduction without altering vegetative growth. - Plant reproductive processes may be more sensitive to chlorsulfuron than growth effects. - Reproductive effects are difficult to recognize and trace to chlorsulfuron because reduced yield may occur below the detection level of conventional chemical analysis. Risks to Plants from Exposure to Contaminated Irrigation Water * Ground and surface water modeling indicate that irrigation water from groundwater or surface water sources, in areas with repeated chlorsulfuron use, may contain levels of chlorsulfuron high enough to adversely effect non-target plants and sensitive agricultural crops. * Chlorsulfuron may adversely effect plant growth and reproduction at such low levels that detecting residues in plant tissues or in soil samples may be extremely difficult or impossible using conventional analytical methods. How the Risk Picture May Change * The Agency will review recently submitted vegetative vigor studies and, provided they meet guideline requirements, incorporate these results into the risk assessment. However, the Agency does not expect these results to alter the conclusions of this assessment. * Additional studies, such as a plant toxicity study simulating far field spray drift exposure to exposing plants to relatively few concentrated droplets of herbicide, may refine the risk estimates for plants exposed to chlorsulfuron drift * Additional plant toxicity studies could refine the Agency’s risk assessment for plants exposed to contaminated irrigation water by comparing the effects from low concentrations of chlorsulfuron in an inch of simulated irrigation water with the effects demonstrated in the vegetative vigor and seedling emergence studies that have already been conducted. Endangered Species Considerations * The Agency will further refine the risk assessment for endangered/threatened plants before making a decision on the reregistration eligibility of chlorsulfuron. * Further analysis of the overlap of individual species with each use site is required prior to determining the likelihood of potential impact to listed species. * The Office of Pesticide Programs recently published on its web site (, an overview of our ecological risk assessment process for threatened and endangered species. Because of the timing of that document, the process described therein was not fully utilized for this screening-level endangered species risk assessment. The Agency will reassess the potential risk of chlorsulfuron use to endangered species using the new process at a later date and consult as appropriate with the U. S. Fish and Wildlife Service or National Marine Fisheries Service at that time. Possible Risk Mitigation Measures * Because of the significant risk to non-target plants, the Agency anticipates mitigation measures may still be needed after the risk assessment has been further refined. * Possible measures include improving product labels to specify: - Maximum application rates - Numbers of application - Methods of application * Measures that may be proposed to control spray drift include: - Specifications on droplet size (large droplet size decreases drift) - Reducing the release height - Implementing wind speed restrictions (slow winds cause less drift) - Disallowing aerial applications - Disallowing applications during stable atmospheric conditions (e.g. temperature inversion) * Measures that may be proposed to control run-off include: - Vegetative buffer zones * Measures to reduce exposure to contaminated irrigation water, such as restricting use of tailwater so that it cannot be used to irrigate other crops. Please do not hesitate to contact me if you have any questions or comments. Cordially, Teung F. Chin, Ph.D. Biological Scientist Office of Pest Management Policy Agricultural Research Service United States Department of Agriculture Located at: APHIS 4700 River Road, Unit 149 (Room 5A66) Riverdale, MD 20737-1237 Phone (301) 734-8943 Fax (301) 734-5992

Responder: Paul Guillebeau
State: GA
Date Requested:
Response: Our published recommendations include chlorsulfuron, but it is used very little in Georgia. Here are the comments I received from our weed specialist (Dr. Stanley Culpepper, in that area. Chlorsulfuron is a wonderful tool for many areas but because of rotational restrictions its use in GA is extremely limited. I am not aware of a single farmer using this technology. There may be some use in continuous grain areas but i am not aware of this.

Responder: Doug Stevenson
State: TX
Date Requested:
Response: Chlorsulfuron (Glean) is essential for economic wheat production in Texas (Smith and Anciso 2000). Texas is the third largest wheat producer in the U.S., harvesting 3.4 million acres annually. The cash value to farmers is $288 million, which generates an additional value-added $973 million for the Texas economy. Texas hard red winter wheat land is commonly fallowed or rotated with other crops (Smith and Anciso 2000). Competition from weeds constitutes the single most important yield-reducing factor in Texas wheat production (Baumann 2003). Most weed competition in Texas wheat is from cool-season annual broadleaf weeds, such as mustards, kochia and Russian thistle. However, other common weed problems include perennial broadleaf weeds, including field bindweed, Texas blueweed and silverleaf nightshade (Baumann 2003). Competition from annual grasses, such as ryegrass, rescue grass and jointed goatgrass also present serious control problems. Crop rotations, fallow and soil tillage are widely practiced as a form of integrated weed management. However, physical, mechanical and cultural practices alone are not sufficient to provide economic weed control in wheat (Baumann 2003). Every year, more than 25% of Texas wheat receives application of herbicides for weed control. Much of this is directed at annual broadleaf weeds. The most common herbicides used in control of annual broadleaf weeds in wheat are 2,4-D and chlorsulfuron. Although 2,4-D is applied most often in Texas wheat (Smith and Anciso 2000, Baumann 2003), chlorsulfuron has gradually replaced 2,4-D in many applications (Salsbury and Bean 1997, Baumann 2003). Applications of 2,4-D at 226.8 g (8 oz) active ingredient per acre provide adequate weed control but present a significant drift haard to non-target plants. Dicamba (Banvel) is often mixed at 3.54 g (1/4 pt = 0.125 oz) with 2,4-D to increase the weed control spectrum (Salsbury and Bean 1997). However, both products present significant drift control hazards to non-target plants, including perennial trees and shrubs, and to sensitive crops such as cotton, melons, grapes, onions and other vegetable crops (Baumann 2003). Dicamba (Banvel) also presents additional carryover problems for rotation to crops such as cotton, onions, peppers, melons and other broadleaf vegetables(Salsbury and Bean 1997, Baumann 2003). Although chlorsulfuron (Glean) is applied alone at the rate of 9.45 g (1/3 oz) per acre, it is most often mixed at the rate of 4.73 g (1/6 oz) chlorsulfuron (Glean) with 2.84 g (0.1 oz) metsulfuron (Ally) to increase the weed control spectrum and reduce the amount of active ingredient per acre(Salsbury and Bean 1997, Baumann 2003). Chlorsulfuron offers the following advantages over 2,4-D: · The drift hazard is much lower. · The hazard to cotton and other sensitive crops is much lower. · It controls weeds resistant or tolerant to 2,4-D and other chlorophenoxy herbicides. · It reduces the overall pesticide load in the environment by 24 - 48 times vs 2,4-D. Practically all of the Texas wheat treated with chlorsulfuron is dryland wheat, and presents no irrigation runoff hazard to non-target plants. The hazard from drift is many times lower than alternative herbicides. Non-herbicidal alternative weed control technologies are not available for weed control in Texas wheat (Baumann 2003 ). References Baumann, P.A. 2003. Weed Control Recommendations in Wheat. Texas Cooperative Extension Bulletin No. B-6139. Salsbury, C. and B. Bean. 2004. Texas Panhandle and South Plains Herbicide Guide for Weed Control in Wheat. Texas Cooperative Extension. Smith, D. and J. Anciso. 2000. Wheat in Texas. Crop Brief on Production, Pests, and Pesticides. Texas Agriculturl Experiment Station and Texas Cooperative Extension. Best wishes, Dr. Douglass E. Stevenson Extension Associate - Ag & Env Safety Texas Cooperative Extension - The Texas A&M Univ. System 115A Agronomy Field Laboratory, TAMU College Station, TX 77843-2488 tel (979) 862-1035 fax (979) 485-2777

Responder: Fred Yelverton
State: NC
Date Requested:
Response: Chlorsulfuron is labeled in turf but has very limited use in North Carolina....much more important in New England and upper midwest. Fred Yelverton Department of Crop Science North Carolina State University

Responder: Robert (Bob) Bellinger
State: SC
Date Requested: May 10, 2005
Not Important/Relevant to my state(s)

Return to Other Requests