The persistence and disappearance by washoff and dryfall of methoxychlor from soybean foliage—a preliminary study

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Abstract
The persistence and disappearance (washoff or dryfall) of methoxychlor [2,2‐bis(p‐methoxypheny1)‐1,1,1‐trichloroethane] from mature soybean [Glycine max (L.) Merrill] foliage was investigated in a small field plot study under natural rainfall conditions in 1977 and 1978. Residue analyses were conducted using whole plant samples‐ Methoxychlor washoff rate was 8±4% of the amount on plants (prior to rain) per centimeter of rainfall, regardless of time after application. Total seasonal washoff for 1978 accounted for 33.5% of the applied pesticide; however, 30.5% of the total loss was removed by washoff on the second day after application. Dryfall or dislodgeable residue accounted for less than 1% of the amount applied. The amount of dryfall was significantly greater in plots entered by workers than in those where entry was avoided. More than 19% of the applied methoxychlor was lost as a result of through‐fall to the ground during application to the plots. Statistical analyses indicated that within‐sample variation for mechanical chopping of plant samples was significantly smaller at the 5% level than for a hand chopping method. Results from this study will be useful in defining research objectives for the development of algorithms to describe the behavior of foliar‐applied compounds. Such algorithms are necessary for estimating runoff losses of insecticides to water bodies.

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