The harvesting of ditch hay (grass and legumes growing along roadsides) has provided livestock owners with a source of forage for years. Tight forage supplies, however, have led to a greater demand for ditch hay than usual this year. If you feed or sell ditch hay, be sure you know what, if any, herbicides were applied to the ditch hay to avoid potential herbicide carryover issues in manure from animals fed the ditch hay.
Products that contain the active ingredients picloram (i.e. Tordon®, Grazon®, and Pathway®), clopyralid (i.e. Stinger, Curtail®, and Transline®), or aminopyralid (i.e. Milestone® and ForeFront®HL) are used to control unwanted broadleaf weeds in cropland, rangeland, pastures, and along roadways. When animals are fed ditch hay that has been treated with these products, these chemicals pass quickly through the animal without significant degradation. Manure and urine from animals that consume grass or hay treated with these products may contain enough herbicide active ingredient to cause injury or death of sensitive broadleaf plants.
Soybean injury from application of aminopyralid-contaminated manure made prior to soybean planting. Photo by Liz Stahl
Be sure to check with the hay supplier or with the local, county, or state agency involved to see if ditches harvested for hay were treated with a herbicide with potential to carryover in livestock manure. A bioassay is recommended or required before a sensitive broadleaf crop (i.e. soybean, lentils, peas, legumes, potatoes, tomatoes or peppers) can be safely planted following application of manure from animals fed ditch hay treated with picloram, clopyralid, or aminopyralid. Refer to the pesticide label for specific restrictions and recommendations.
The article, "Harvesting Ditch Hay", discusses this issue in greater depth. Although the article focuses on picloram and clopyralid, aminopyralid (released after the publication was created) has similar potential to cause injury to sensitive broadleaf crops from contaminated manure.
Awareness and communication can go a long ways in helping prevent manure from becoming contaminated in the first place, as well as help prevent contaminated manure from causing problems in the future.