Harvesting ditch hay (grass and legumes growing alongside the roadways) is a common practice, especially in western Minnesota . Ditch hay provides livestock owners with forage suitable for beef cattle, dairy heifers and horses. However, in recent years, there have been several cases of significant soybean injury as a result of manure applications from livestock fed ditch hay that was treated with picloram or clopyralid. This injury has reduced grain yields, and in some cases, resulted in total yield loss.

Picloram (commonly sold as Tordon and Grazon) and clopyralid (commonly sold as Stinger, Curtail and Transline) are used to control unwanted broadleaf weeds on cropland, rangeland, pastures, and along roadways. These products may also be used in formulations with other herbicides such as bromoxynil, diuron, 2,4-D, MCPA, triclorpyr, and atrazine. These herbicides are especially popular with local and state highway departments because they control hard-to-kill noxious weeds like thistles and leafy spurge but do not kill beneficial or planted roadway grasses. Highway departments are required to control noxious weeds under the State’s Noxious Weed Law.

When animals are fed ditch hay that has been treated with either picloram or clopyralid, these chemicals pass quickly through the animal without significant degradation and end up in the manure via the urine, usually within a day or two. Manure application to agriculture production fields is a beneficial and common practice. However, if sensitive crops (i.e. soybeans, lentils, peas, legumes, potatoes, tomatoes or peppers) are planted in fields where contaminated manure has been applied, injury or crop death can occur. Clopyralid and picloram both have a growth regulator mode of action. Typical injury symptoms are twisting (epinasty) of plants and cupping of leaves. Injury symptoms can also include a loss of apical dominance (short plants) and abnormal side shoots.

Close-up photo of soybean injury as a result of Tordon contaminated manure application to the field prior to soybean planting. Notice the cupping of the growing point. Photo by Bruce Potter.

The labels of products containing picloram state that when roadways are to be grazed by animals, do not apply more than 2 gallons of product/acre. The labels also state to not allow lactating dairy animals to graze treated areas within 7 days after application and that meat animals should be withdrawn from treated fields at least 3 days before slaughter. The label also states not to harvest or cut the forage within 30 days after application. There are no label restrictions on grazing or hay harvest following application at labeled rates for products containing clopyralid. However, clopyralid labels do state to not plant sensitive broadleaf crops in treated areas until a sensitive bioassay shows that no detectable clopyralid is present in the soil. Both picloram and clopyralid labels carry important precautions that ditch hay harvesters and feeders need to be aware of: 1. manure and urine containing these herbicides may cause injury to sensitive broadleaf plants and 2. plant material containing these products should not be used in compost.

Both herbicides are persistent and mobile in the soil, are readily absorbed and translocated throughout the plant, and remain chemically stable and intact in plants. Picloram and clopyralid have been detected in the groundwater, but only picloram has been detected in groundwater in Minnesota . Picloram has a field half-life (the time required for one-half of the herbicide to break down) of 20 to 300 days with an estimated average of 90 days . Clopyralid has a field half-life averaging 40 days, with a range of 12 to 70 days, and can persist in the soil for up to 14 months depending on soil type, climate and other factors. The label for Curtail (clopyralid and 2,4-D) cautions that in drier areas of reduced microbial activity, sensitive crops may be injured for up to four years after application. Because of these characteristics, products containing clopyralid and picloram carry a crop rotation restriction of 18 months for sensitive broadleaf crops, or approximately two growing seasons in Minnesota . However, researchers in other states who have dealt with treated ditch hay issues insist that relying solely on herbicide label restrictions is not enough to protect sensitive crops treated with contaminated manure or compost. They recommend soil analysis to detect clopyralid and picloram prior to planting sensitive crops.

Soybean injury in Montevideo , MN in 2004. Horses were fed ditch hay that had been sprayed with Tordon, and manure was spread onto a field where sensitive soybeans were later planted. Injured plants represent areas where manure was spread (note uneven application pattern). Photo by Bruce Potter.

Even though these products cause injury to sensitive crops, there is no documented history of human or livestock toxicity by picloram or clopyralid.

Composting or storing manure that contains clopyralid and picloram may not speed herbicide degradation, as these products do not break down quickly in compost. In these situations, the concentration of both herbicides in relation to the organic matter can increase initially while the manure is stored or composted. Studies are currently being conducted at Washington State University to determine how long these products need to be composted before they are undetectable or detectable in low amounts. Currently, it is believed that clopyralid can remain in manure, forage/feedstuffs or compost for several years. Therefore, composting contaminated manure is not a solution for this problem. However, you can spread contaminated manure/compost on fields that will be planted into a non-sensitive crop like corn, sorghum or small grains.

Better awareness and communication is needed between local and state highway departments and farmers harvesting, feeding and selling ditch hay. Livestock owners buying ditch hay also need to ask the hay supplier if the harvested hay came from an area treated with one of these herbicides. It is best to ask for a written statement if possible. If manure containing clopyralid or picloram is spread on agricultural fields, only non-susceptible crops (like corn, small grains or sorghum- sudan forage) should be grown for 18 months.

Farmers need a permit to hay highway areas that MN Department of Transportation (MN DOT) owns. Along sections of Interstate 90, farmers bid and pay for the right to harvest roadways. Permits are not needed on roadways where only an easement is owned by MN DOT. The permit is free, and by contacting MN DOT and obtaining the permit, the farmer will be notified of any cutting restrictions that are due to herbicide use, wildlife habitat designation and/or calendar date restrictions. For contact information regarding the permit, visit: www.dot.state.mn.us/tecsup/utility/files/permits_contacts.pdf. Roadways owned by county and local governments have their own regulations, and farmers should contact their County or Township to obtain any cutting restriction information prior to harvest.

Two labs have worked with Washington State University (which has dealt with this problem in their University compost since 2000) to develop sensitive analyses for clopyralid and picloram. Anatek Labs Inc (208-883-2839) in Idaho and Morse Laboratories Inc (916-481-3141) in California will test forage and soil samples for the presence of clopyralid to 1 part per billion (ppb) and will screen for the presence of picloram. The tests cost approximately $150 and take about a month to complete. It is important to contact the companies for instructions on correctly sampling forage and soil for these tests. For a list of additional labs that may provide this service, visit http://weeds.cropsci.uiuc.edu/newsletter/misc%20articles/labanalysis.htm. When checking for other labs that test for these chemicals, be sure to verify how sensitive their tests are. Crop injury can occur at levels of 10 ppb or less.

If crop damage occurs due to manure/compost contamination by clopyralid and/or picloram, the individual who harvested the hay is usually the person responsible, especially if a permit/permission was needed and not obtained. If buying ditch hay, buyers should specifically ask where the hay was harvested and if the individual selling/harvesting the hay is aware of any herbicides used. However, legal advice outside of this article should be obtained in cases where injury to sensitive crops occurs.

The following references were consulted for this article:

Bezdicek, D., M. Fauci, D. Caldwell, and R. Finch. 2000. Compost Quality: New Threats from Persistent Herbicides. Agrichemical and Environmental News, October 2000, Issue No. 174. www.compost.wsu.edu.

Bezdicek, D. 2001. Copyralid in Compost - an Internal Report. www.compost.wsu.edu

Bezdicek, D., M. Fauci, D. Caldwell, R. Finch and J. Lang. 2001.   Persistent Herbicides in Compost Special Report: Composters Combat Clopyralid. Biocycle, page 25. www.compost.wsu.edu.

Brinton, William F and T. Craig Blewett 2005. Presence, fate, and effects of clopyralid and other anthropogenic residues in green waste composting. Paper 4A-21 In A. R. Gavaskar and A.S.C. Chen (Eds). Remediation of Chlorinated and Recalcitrant Compounds- 2004. Proceedings of the fourth International Conference of Chlorinated and Recalcitrant Compounds ( Monterey , CA ; May 2004) ISBN 1-57477-145-0, published by Battelle Press, Columbus , OH

Cox, C. 1998. Picloram, Herbicide Fact Sheet. Journal of Pesticide Reform, 18:1 pages 13-20. www.pesticide.org/picloram.pdf

Cox, C. 1998. Clopyralid, Herbicide Fact Sheet. Journal of Pesticide Reform, 18:4 pages 15-19. www.pesticide.org/clopyralid.pdf

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