Q: I made an application of Weed-B-Gone herbicide to my horse pasture. After application, I noticed it was labeled only for use on lawns (turf) and not horse pastures. When can I graze again?
A: It is extremely important to read the herbicide label prior to application; the label is the law. Herbicides are labeled for application to a specific site(s). Unfortunately, since Weed-B-Gone is not labeled for use in a pasture, there are two issues to consider, legality and safety.
You have made an "off-label" application, this is illegal. If the off-label application is reported to the Minnesota Department of Agriculture (MDA) (the agency charged with enforcing pesticide laws), an investigation would be opened, and there is the possibility of fines and penalties for the applicator. One benefit of involving the MDA is they take soil and plant samples to help determine when it is safe to graze. Because Weed-B-Gone is not labeled for pastures, the label does not include information on grazing restrictions.
The second issue is horse safety. If you choose not to report the off-label application, it is up to you to determine when it is safe to graze. To help determine this, look at the active and inert ingredients in the herbicide and see if they are found in any herbicides labeled for pasture use. Herbicides labeled for pasture use have information on grazing restrictions; this can be used to determine when to graze again, however, this will not ensure your pasture is safe to graze. You can also submit soil and plant samples to a laboratory for pesticide residue analysis. The herbicide manufacture might also have information related to off-label applications; a phone number is usually listed on the label.
Before a herbicide is purchased, the label should be thoroughly red and the applicator should ensure the desired application site is listed. Most herbicide labels are available online.
By Krishona Martinson, PhD, University of Minnesota