Beware of what you add to Your Compost!

Posted: April 29, 2011

Do you know which herbicides were used to manage weeds in forages before they were incorporated into a compost pile? If not, you may be in for a disappointing growing season.
Herbicide injury on a tomato plant. (Photo courtesy of Andy Beck.)

Herbicide injury on a tomato plant. (Photo courtesy of Andy Beck.)

A grower recently called my extension office describing symptoms of herbicide damage that appeared on his tomatoes transplants. The plants were grown from seed during the winter months and then transplanted into the soil under a heated plastic hoop house. After examining the plant material it was evident that some type of herbicide had caused the damage. However, the grower claimed no herbicide was applied to the plants at any point during the growing process. In fact, the only application made was a mixture of composted horse manure and hay incorporated into the soil a few months prior to planting.

Composted horse manure containing dried hay, is often considered a valuable nutrient resource for its soil amending characteristics. Knowing what herbicides have been used to manage weed populations is crucial before using it as a soil amendment. Herbicides that contain pyridine carboxylic acid (aminopyralid, clopyralid, fluroxypyr, picloram, and triclopyr) can remain active in manure piles, unworked compost piles, and forages which are dried and baled. As you can see from the picture, it’s doubtful these tomatoes will provide adequate yields this summer.

Prepared by Andy Beck, Penn State Extension, Schuylkill and Berks Counties