Dissipation of Alachlor, Metolachlor, and Atrazine from Starch-Encapsulated Formulations in a Sandy Loam Soil

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Abstract
Research was conducted to determine the effect of starch encapsulation on soil dissipation and weed control with alachlor, metolachlor, and atrazine on an Estherville sandy loam in the field. Starch encapsulation increased persistence of alachlor in the surface 15 cm of soil compared to the emulsifiable concentrate formulation during the first 60 d after treatment More alachlor was detected 30 to 75 cm deep with emulsifiable concentrate than the starch-encapsulated formulation 30 d after treatment. Little alachlor was detected below 15 cm thereafter. Starch encapsulation also increased persistence of metolachlor in the surface 15 cm, but reduced concentrations at 15 to 30 cm compared to the emulsifiable concentrate 30 d after treatment. By 120 and 340 d after treatment, metolachlor concentrations at 15 to 30 cm were greater with starch-encapsulated than emulsifiable concentrate formulation. Starch encapsulation greatly increased atrazine persistence in the surface 15 cm compared to the dry flowable formulation. Although encapsulation increased atrazine concentration in the surface 15 cm, it reduced the concentration below 15 cm compared to the dry flowable formulation 30 and 60 d after treatment However, by 120 and 340 d after treatment, starch encapsulation often resulted in greater atrazine concentrations below 15 cm than the dry flowable formulation. Control of green foxtail and redroot pigweed with starch-encapsulated herbicides was similar or superior to the commercial formulations.