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CATHIE DRAINE: Simple process allows gardeners to test for herbicides
On March 1 Rapid City reissued the Yard Waste Compost Advisory. There are still persistent herbicides in the city compost materials. The landfill feels these three chemicals, clopyralid, (clow-PEER-a-lid), Quinclorac (kwin-CLOOR-ack) and MCPP are coming into the landfill in the feedstocks (such as manure, straw, lawn grass, hay). Gardeners are being advised NOT to use the compost on ANY broad-leafed plant. It can, however, be used with no damage on lawns. This is not a problem unique to the Rapid City landfill. Persistent herbicides in compost have been a growing concern worldwide for the last twenty years. Persistent herbicides, which bond to organic residues in the soil, can remain active in the soil from 30 days to three or four years.While some chemicals break down easily, these do not. The efficacy of the chemicals is affected by sunlight, moisture, soil microbes and heat and because so many factors are involved in the mitigating process, it is different for each soil and situation.Gardeners do have choices. They can learn to compost their own lawn, garden and clean kitchen waste. This can be a no cost, low work, relatively small space project. They can find a manure, hay, grass source and confirm that it is safe and free from the offending herbicides. Unfortunately, this information can be hard to obtain because, for example, the vendor of hay may not know what chemicals the grower of hay might have applied. Additionally, the homeowner has a growing responsibility to know what is being applied to his lawn, by himself as the applier or what is done by a lawn service.Another option, which is recommended by almost all sources, is to perform a bioassay, a simple process that can determine if the soil is free of the herbicide. I feel strongly that this is an easy pre-growing test that we all should begin to do regularly. And, frankly, at this time it is the only relatively quick assurance that our garden soils, manures, mulches, compost are good to use.These directions for a bioassay test are as given by Montana State University and included in their pesticide safety education (Pesticides.montana.edu).Materials• Test material (soil amendment or topsoil)• Potting mix (commercial, compost-free, peat-based mix)• Plastic pots• Plastic saucers• Garden pea seeds• Plastic bags• Disposable glovesInstructions1. Set up control pots. Fill three pots with potting mix. Label.2. Prepare test pots. Fill three pots with test material. If testing compost or manure mix two parts test material to one part potting mix in a clean plastic bag. Label pots.3. Plant three pea seeds in each pot just under the material’s surface. (Pea or bean seeds are recommended because they germinate quickly.) Record planting date. Place each pot on an individual saucer.4. Grow plants. All pots should have similar growing conditions with consistent light, temperature and water.5. Evaluate plants. Record germination dates for each pot (two seeds must germinate to record). Grow until three sets of leaves appear (14-21 days). Compare plants grown in test material to control pots (potting mix).To get a good sense of the scientific activity around the mitigation of persistent herbicides, consult the information available on www.compostingcouncil.org. To access numerous Extension papers on this topic from around the country, enter this exact phrase in your search: “information on persistent chemicals in garden soil and compost and extension.”I would assume that commercially available bagged compost was free of persistent herbicide contamination. Personally, I would be more careful and would bioassay bagged steer manure because there is no way of knowing the sources of their feed in the feedlots. And it seems that animals not only pass herbicides through their systems untouched but that it will then be more concentrated in their manure than in the original feed.Cathie Draine is a South Dakota Cooperative Extension Master Gardener and a member of the Garden Writers Association. She lives and gardens in Whispering Pines. Contact her at blackhillsgarden.com.
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