In 2014, one of the Seed2Need gardens showed signs of herbicide damage. The tomatoes had narrow, fern-like foliage and other plant varieties had cupped leaves and twisted stems. We sent plant samples to NMSU for testing and they diagnosed the problem as herbicide damage caused by applying manure on the gardens from animals that had consumed hay harvested from a pasture treated with a broad leaf herbicide containing picloram, clopyralid or aminopyralid. These herbicides can pass through the animal’s digestive tract and remain active in the manure long after it is composted.
Many livestock and horse owners purchase hay rather than growing it themselves. Often, they don’t know that their hay is contaminated with herbicide. That presents a problem for gardeners who use this manure in their vegetable and flower gardens.
To avoid herbicide contamination, always do an Assay test on manure or compost before using it. For instructions on how to conduct an Assay test, check out North Carolina Extension office’s instructions (pdf download).
If your compost or manure is contaminated with herbicide, do not use it. Contact your local agricultural extension office for advice on how to properly dispose of it.
If your garden soil is contaminated, Clemson University suggests spreading activated charcoal on the contaminated field to deactivate the herbicide. This is a messy process and it does not work overnight. After treating the garden with activated charcoal, very few plants showed signs of herbicide damage the following season. The plants that were damaged were on the outside edge of the garden so it is likely that we simply missed a few spots.