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[RC] Weed Free Hay/interesting article part I.5 - heidi larsonFrom BioCycle Journal of Composting &Organics Recycling July 2001, Page 25 ONE YEAR LATER PERSISTENT HERBICIDES IN COMPOST This analysis of the Dow chemical products that caused problems at two Washington state composting facilities, proves that protective steps need to be taken. David Bezdicek, Mary Fauci, Dan Caldwell, Rick Finch and Jessie Lang ONE YEAR has passed since the Washington State University (WSU) composting facility and the Spokane Regional Compost Facility discovered traces of persistent herbicides in their composts. In Spokane, the source of contamination is a compound called clopyralid. Compost contamination at WSU initially involved the herbicide picloram, but clopyralid has since been detected in the compost also. In both cases, the compost damaged sensitive plants at local gardens and nurseries. Several articles published at that time brought the issues to the forefront (see “Dealing with Herbicide Residues in Compost,” September, 2000 BioCycle and also the references, Bezdicek, et al. 2000, and Miltner and Stahnke, 2000). Clopyralid contamination has since been reported at a yard trimmings facility in Cheney, Washington and at a horse facility in Whitman County Washington. Incidents in Pennsylvania and New Zealand have also come to light. Today, both the WSU and Spokane facilities are still dealing with the problem of persistent herbicides. Facility managers, regulators, public agencies, researchers and the herbicide manufacturer continue to seek solutions to the problem, ranging from on-site treatment to regional product bans. THE CULPRITS – CLOPYRALID AND PICLORAM Clopyralid is an active ingredient in several herbicide products that have a wide variety of applications (Table 1). The most prominent product, and the one implicated in the Spokane situation, is Confront, made by Dow AgroSciences (Dow). Confront is used on lawns to control dandelions, clover, and other broadleaf plants. It was introduced in 1989 to replace existing herbicides that required multiple applications — from three to five applications per season to one or two. Clopyralid also is registered in a number of formulations used on cereals, grass hay, sugar beets, mint, asparagus, strawberry, blueberry and Christmas trees. At WSU, the source of clopyralid contamination is believed to be from grass hay and straw, purchased for its livestock operations on and off campus. Thus clopyralid is a potential concern for composting facilities taking yard trimmings or agricultural feedstocks. Picloram is used to control weeds for agricultural and industrial applications including pasture, rangeland, railroads and power lines. It is the less worrisome of the two herbicides since treated residuals are less likely to be collected for composting. Clopyralid and picloram are classified as pyridine carboxylic acid herbicides (see Figure 1). They are growth-regulator type herbicides. Like 2,4-D and dicamba, they work by mimicking plant growth hormones called auxins. The effect of these chemicals is to cause the plant to grow abnormally. They are quite water soluble and mobile in soil. One advantage of these chemicals is their low toxicity for animals, including humans. Typical symptoms of clopyralid phytotoxicity are shown in Figure 2. Although plants may appear normal, the loss of “apical dominance” will likely prevent fruit set. Some leaves that are supposed to be compound become single leaves. Side shoots may develop where they should not be. In legumes, cupping is a typical symptom and trifoliate leaves fail to develop. The most susceptible crops can be sensitive to clopyralid at the ppb level. Clopyralid is extremely toxic to sunflower, legume crops and solanaceous plants, including tomatoes and potatoes. Effects on these plants can be seen at levels of 10 parts per billion (ppb) or less. According to Dow’s literature, this is roughly 100 times lower than the tolerance allowed on asparagus, 50,000 times lower than the tolerance allowed on grasses, and 300 times lower than allowed on barley grain. Concentrations above these low levels are seldom seen in the real world, but they point out the potential for contaminated feedstocks to affect sensitive crops. . o o o o . o_ \ \____ o_ \_\ . (*)~(*)\_______/ . / \ . \______/ / . \_______/\ /- . o-- /_/ \ / . / \ / / . o o o-- / . / \ . o o heidi larson =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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