Long-term persistence of aminocyclopyra-chlor and clopyralid during the composting of Yard trimmings

Certain pyridine carboxylic acid herbicides, including clopyralid, aminocyclopyrachlor and, aminopyralid that have recently been introduced, have been found to be recalcitrant in soil and composts. These herbicides are generally usedfor broadleaf weed control in pastures, lawns and natural areas. Certain types of plants, including tomatoes and beansare very sensitive to residues of these compounds even at very low concentrations.

Further Authors:
Y M Li - The Ohio State University
S K Grewal - The Ohio State University

To better understand the impact of the use of these compounds on composts, we determined the persistence of granular and liquid formulations ofaminocyclopyrachlor (tradename imprelis), and clopyralid during long-term composting of mixtures of grass andleaves. Herbicide treated turfgrass plots were established that received one of four treatments: no herbicide,aminocyclopyrachlor granular application (84 g AE/ha), aminocyclopyrachlor as liquid spray (84 g AE/ha), orclopyralid (209 g AE/ha) as a liquid spray. Grass clippings were collected from each plot within 7 days after herbicideapplication. The treated grass samples were mixed with leaves (2:1 L:G ratio) and composted under conditions thatsimulated commercial windrow composting conditions for 178 days. A system of triplicate 4 liter compost reactorswere used each containing 1.2 kg of wet compost. The reactors were incubated at 55ºC (±2 ºC). Aeration wasmaintained at 100 ml/min and CO2 concentrations were measured hourly. The grass and leaf samples, plus samplesremoved from the reactors on days 0, 10, 30, 50, 78, 100 and 178, were analyzed for pH, moisture, ash, volatile solids,total carbon and nitrogen, and aminocyclopyrachlor and clopyralid concentrations. Results showed that 58 and 47 % ofthe aminocyclopyrachlor was lost after 178 days of composting from the liquid and granular formulations respectively.By comparison, 70% of the clopyralid was lost over the same period. A second experiment in large scale reactors (75 kgcompost) with aminocyclopyrachlor at two different concentrations showed similar results. To evaluate theirphytotoxicity, each of the final composts were used at 4, 10 and 20% amendment levels in potting media into whichseeds of bean and tomato were sown. Composts made from yard trimmings that did not receive a herbicide applicationand ProMix without compost were used as controls. Results showed that none of the composts had a significant effecton tomato or cucumber seed germination. However at the 10 and 20% levels, bean germination was reducedsignificantly by more than 50%. The aminocyclopyrachlor containing composts reduced plant height, shoot dry weightand leaf area of both bean and tomato to some degree. Various symptoms of herbicide toxicity were evident on theaffected plants. Beans were more sensitive to imprelis while tomatoes were more sensitive to clopyralid. These resultsindicate that in certain cases, imprelis or clopyralid applied to grass may not degrade to a sufficient extent during Long term composting to be used in gardens or in plant growth media.

Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 8
Preis inkl. MwSt.: € 8,00
Autor: F C Michel

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