Manure – Testing For Herbicide

Q: I was interested in your radio comments about using straw treated with Grazon for mulch under tomato plants and the resulting curly leaves. I use manure from a local farm and have had problems. How do I get rid of the residue as quickly as possible?

A: Time is about the only thing that eliminates the residue. The product’s half-life in soil is more than 100 days. Tilling, to expose chemicals to sunshine and oxygen, and watering, to dilute them, help degrade the herbicide. The best way to test for herbicides in manure is to plant three bean seeds or a small tomato transplant in a pot filled with a 1:1 mix of manure and potting soil. Water, and let them grow for two to three weeks. If the plants grow normally you can assume the manure is safe to use.