Matthew F. Stephens
County Agent, Jackson Parish
I got a call from one of the LSU AgCenter county agents asking if I could meet him at someone’s place and look at some barnyard compost that seemed to be killing the man’s tomato plants. “How could barnyard compost be killing tomato plants?” I thought to myself on the way out to meet the county agent. The only thing that I had seen before was too much nitrogen rich manure that burned the plant. This would be easily corrected by tilling the manure in with the soil.
Once we got there and stared looking, asking questions, sending dozens of pictures to our horticultural specialists and scratching our heads, it hit us like a ton of bricks. We have just seen our first “real life” case of herbicide damage from barnyard compost. The uneaten cow hay that was piled up from the feeding area, mixed in with the manure and composted had been treated with a herbicide called Grazon® containing 2,4-D and picloram. These two chemicals are no threat to humans or animals, but death on plants like tomatoes, squash, peas, beans, eggplants, potatoes and peppers.
One may say, “I don’t have any worries because I don’t use this product on my yard”…. Wrong!! There are other herbicides that have a longer residual life than the two previously mentioned. One that is making its presence known in composting blunders is a chemical called clopyralid. Clopyrid is a pre- and post-emergence herbicide with activity against a narrow range of certain annual and perennial broadleaf weeds. The chemical has been on the market for almost 20 years and sold under many different trade names. A few of the names that may sound familiar are Confront® (turfgrass), Lontrel® (turfgrass), Reclaim® (turfgrass), Stinger® (agricultural uses) and Transline® (industrial right-of-ways). Clopyralid has excellent activity on certain difficult-to-control leguminous weeds. In turfgrass it is particularly effective in controlling clovers and dandelions. The fact that it has a long residual effect is a double-edged sword. On the good side, fewer applications are needed for weed control. The bad thing is that grass clippings from lawns treated with clopyralid should not be used for compost intended for bedding plants that are susceptible to the chemical. The list of plants that are susceptible makes up an average of 80 percent of the basic home garden.
Other herbicides utilized in yards, hay fields or other agricultural crops that may cause problems in compost intended for gardens and flower beds are 2,4-D (Weed-B-Gone®, Hi-Dep®, Weedar®) and picloram (Grazon®, Tordon®). Although these herbicides are lethal to certain plants, they do not affect animals eating grass or hay that has been treated.
People who use compost for gardens and flower beds should be sure that grass clippings or other plant material used as feedstocks have not been treated with these herbicides. For more information on herbicide persistence, gardening or composting, contact your local LSU AgCenter Cooperative Extension Office or visit the LSU AgCenter Web site.