Leachability and Efficacy of Starch-Encapsulated Atrazine

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Abstract
Controlled-release formulations have the potential to reduce atrazine leaching but may reduce herbicide bioavailability and weed control. This research was conducted to determine if starch-encapsulated atrazine produced by the extrusion process could be modified to provide an optimum rate of herbicide release for adequate weed control and reduced leaching potential in sandy soils. The dry flowable (DF) and six starch-encapsulated atrazine formulations of various mesh size (14 to 20 and 20 to 40), clay content (0 and 5%), and extruder processing speed (200 and 400 rpm) were evaluated. All starch encapsulations reduced the amount of atrazine leaching from the surface 5 cm of soil columns by an average of 68% compared with the dry flowable formulation. Compared with the larger starch granules (14 to 20 mesh) 8% more atrazine in the smaller granules leached from the surface 5 cm. Atrazine efficacy was measured using an oat bioassay conducted in the greenhouse. Smaller granules (20 to 40 mesh) provided equivalent efficacy to DF while large granules (14 to 20 mesh) did not. Extruder speed and clay content did not affect efficacy or leaching potential. This study indicates that finer starch granules should result in faster atrazine release and improved weed control while still reducing the leaching potential of atrazine.

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