Submitted to: Proceedings of American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: April 28, 2004
Publication Date: March 28, 2004
Citation: Potter, T.L., Strickland, T.C., Culbreath, A. Implications of multiple applications on cropped plots to terrestrial field dissipation study design [abstract]. Division of Agrochemicals for the 227th American Chemical Society National Meeting. Technical Abstract: Determining the dissipation rate of parent compounds (and some metabolites) under actual use conditions is a primary objective of terrestrial field dissipation (TFD) studies. Row-crop preemergence herbicides provide the simplest case. Traditional TFD study guidelines which involve a single application to bare soil appear well suited to address this use scenario. This is not the case of most insecticides and fungicices. Multiple applications on or within plant canopies during the growing season are common. Effective simulation of use scenarios of this type requies that foliar inception and foliar processes such as wash-off and direct volatilization and photochemical transformation be taken into account. An assessment of impacts of repeated as opposed to single applications on processes such as soil degradation also appears necessary. Data obtained in a recently completed study involving triazole fungicide use on peanuts in Georgia will be discussed. Canopy and soil loading rates after 7 sprays spaced 2 weeks apart starting at emergence to 2 weeks prior to digging were made. This was combined with a series of aerobic laboratory soil incubations. Results provide a quantitative assessment of canopy inception as function of crop growth stage and demonstrated relatively rapid adaptation of the soil microbial community to active ingredient degradation. There was a 2 to 3X decrease in 1st order half-lives. The implications of these results for TFD study design and guideline development will be addressed.