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April 24, 2024 - Residual Herbicides Leaving a Mark

How to avoid damage to gardens and non-target vegetation.

On occasion at Agriculture Services, we receive calls about potential herbicide damage to vegetable, fruit, or flower crops in local gardens. More often than not the problem is a result of natural causes due to insects or plant diseases. In rare instances the damage to plants may be from herbicide drift or carryover in manure or compost.

Symptoms can include poor seed germination; death of young plants; twisted, cupped, and elongated leaves; misshapen fruit and reduced yields. If in fact herbicides are the cause, then it may be due to a class of products known as pyridine carboxylic acids, which include Aminopyralid, clopyralid, fluroxypyr, picloram and triclopyr.

Designed to help farmers and ranchers control invasive broad leaf weeds, residual herbicides control the proliferation of invasive species. Left unchecked, these species negatively impact the environment and food production by reducing biodiversity and crop yields.

When applied to pasture, hay or cereal crops, these products can be safely consumed by horses and livestock without negative effects because they are not fat soluble. They pass through the digestive tract and are excreted in urine and manure.

The chemicals of greatest concern are picloram, clopyralid and aminopyralid as they can remain active in hay, grass clippings, piles of manure and compost for a long period of time. These herbicides eventually break down through exposure to sunlight, soil microbes, heat, and moisture in as little as thirty days, or they can last several years.

When mulches, manure or compost with residual herbicides are applied to fields or gardens serious damage can occur. When used as directed on the label these herbicides should not cause problems. Issues arise when affected materials are sold or given to others who have no knowledge of the herbicides used or the adverse effects they can have on other plants.

Producers who give away or sell manure, compost, or mulch, should make sure to be aware of any potential herbicide use and let their buyers know. Even treated hay or straw that is several years old should not be given away or sold to make mulch or compost. Anyone purchasing forage for livestock use should be informed of the potential that the herbicide will pass through the digestive tract of their animals and be deposited in pastures or barns.

Buyers on the other hand, should ask the farmer or seller if the products or materials have been treated with herbicide, inquiring about details of the herbicides used. Ask what animals had been fed and the origin of the hay or feed. If uncertain of whether herbicides were used, buyers can have products tested at a local lab.

All parties need to be aware of potential herbicide carryover in a variety of materials and products whether from on farm or in bagged form from a feed or garden outlet. If contaminated products are inadvertently purchased, they may be spread on grass pasture to facilitate the breakdown of the herbicide, so that the product may be incorporated into soils at a later date.

Herbicides are an integral tool for the successful management of foreign invasive species that would otherwise have a tremendous negative impact on the environment, economy, and food production. Awareness and education are the keys to responsible management of these products on the part of producers and consumers alike.