Herbicide Carryover Caution
The North Carolina Cooperative Extension is alerting farmers, gardeners, livestock owners and hay producers to the danger to vegetable and flower crops caused by applying horse and other livestock manure to the soil.
The problem is caused by a certain class of herbicide, which remains active in the manure.
The bottom line is that the herbicide is not toxic to horses or people. According to Elena Eller, agricultural extension agent for livestock and youth in Moore County, the herbicide “only affects the metabolism of plants.”
“It is not absorbed into a horse’s system, so it has no grazing restrictions,” she said. “The problem is if the manure is used in gardens or on clover or alfalfa fields, the herbicide prevents plants from growing.”
According a Cooperative Extension bulletin, “The herbicides of concern, aminopyralid, clopyralid, fluroxypyr, picloram and triclopyr, are in a class of herbicides known as pyridine carboxylic acids. They are registered for application to pasture, grain crops, nonresidential lawns, certain vegetables and fruits and roadsides. They are used to control a wide variety of broadleaf weeds, including several toxic plants that can sicken or kill animals that graze them or eat them in hay.
“Based on USDA-EPA and European Union agency evaluations, when these herbicides are applied to hay fields or pasture, the forage can be safely consumed by horses and livestock — including livestock produced for human consumption.
“They can remain active in the manure even after it is composted. They can also remain active on hay, straw and grass clippings taken from treated areas. The herbicides leach into the soil with rainfall, irrigation and dew. As with many other herbicides, they can remain active in the treated soil.
“The herbicides of particular concern include aminopyralid (Forefront, Milestone), clopyralid (Curtail, Redeem R&P), and picloram (Grazon P&D, Surmount).”
Cooperative Extension suggests a few general guidelines to follow in order to utilize these herbicides in a responsible manner.
n Custom applicators should tell their clients what herbicides are applied to the fields and provide them with a copy of the product label.
n If you sell hay, tell livestock owner that the herbicide will pass through into the manure and that the manure will not be usable as fertilizer for broadleaf plants or in compost. Manure may be spread only on grass pastures or grass hayfields.
n Don’t give away old hay or grass clippings for use as mulch or in compost. The herbicide will still be active on the hay itself.
n If you buy hay for your livestock, ask the seller which herbicides they used and familiarize yourself with the product label. If you cannot obtain the history of the hay, do not sell or give away manure for use on anything other than a grass pasture or hayfield.
n If you are a gardener or farmer, do not use manure or compost to grow sensitive crops without knowing the herbicide history. Communicate with suppliers of manure, compost, hay and grass clippings to determine what herbicides they used, or where they obtained hay fed to livestock.
Product labels can be found at the following website: www.cdms.net/LabelsMsds/LMDefault.aspx.
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