Soybean Injury
Picloram (commonly sold as Tordon, Grazon, and Pathway) and clopyralid (commonly sold as Stinger, Curtail, and Transline) are used to control unwanted broadleaf weeds on cropland, rangeland, pastures, and along roadways. These herbicides are especially popular with local, county, 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.

Recently labeled herbicides containing the active ingredient aminopyralid (commonly sold as Milestone, Milestone VM, and ForeFront R&P) are beginning to replace picloram and clopyralid in many roadside treatment programs due to increased Canada thistle control with aminopyralid. Aminopyralid is in the same herbicide family as picloram and clopyralid, and poses the same potential to cause injury to broadleaf crops from contaminated manures. However, sensitive crop injury from aminopyralid contaminated manure has not yet been reported in Minnesota.

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. 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 (Figure 2). Injured plants can exhibit twisting (epinasty), leaf cupping, and loss of apical dominance, resulting in short plants and abnormal side shoots.

Labels of many products containing picloram and clopyralid list restrictions 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,
2. since plant material containing these products does not break down more rapidly in compost, treated plant material containing these products should not be used in or for compost, and
3. picloram and/or clopyralid contaminated manure and/or compost should not be spread on land used for growing susceptible crops. Contaminated manure may be spread onto fields that will be planted to grass crops (i.e. corn, small grains, or sorghum sudan forage).

Herbicide labels for products containing picloram and clopyralid may have slightly different warnings or recommendations based on the product formulation and/or active ingredient concentration. Some examples of warning and recommendations for these products include:

• do not allow lactating dairy animals to graze treated areas within 7 days after application;
• meat animals should be withdrawn from treated fields at least 3 days before slaughter;
• and, do not harvest or cut the forage within 30 days after application.
  

Better awareness and communication is needed between local, county, and state highway departments and farmers harvesting, feeding and selling ditch hay.

If you are harvesting ditch hay, develop a working relationship with your county weed inspector or highway department to:

• identify which herbicides are used in the roadside weed control program,
• determine which roadsides are spot treated and if some areas have broadcast treatments, and
• dates when roadsides will be treated.

By working together with local, county, and state agencies, hay harvesters can reduce the risk of harvesting forages with unwanted herbicide residues. If the harvest and/or grazing restrictions for the herbicides are communicated to, and followed by farmers harvesting ditch hay, the forage can be fed to livestock without contaminating manure.

For more information on picloram or clopyralid contaminated ditch hay:
http://www.extension.umn.edu/cropenews/2005/05MNCN43.htm

Krishona Martinson, PhD,
Regional Extension Educators
University of Minnesota Extension