Entrapment of herbicides in starch for spray applications

Abstract Sprayable controlled-release formulations were made with the herbicides trifluralin, 2,4-D ester, alachlor and butylate. Aqueous dispersions of gelatinized cornstarches or flours containing herbicides were sprayed and dried to water-resistant films that entrapped the herbicide. Formulations containing 3% Miragel®, 3% cooked pearl, or 7% pregelatinized corn flour and one tenth these levels of active ingredient (a.i.) provided as emulsifiable concentrates had stable viscosities in the 75–260 cP range over 24 hours. The best entrapment was obtained by cooking 3% starches or flours at least 30 min at 100° C and dispersing the emulsifiable concentrates into the cooled whole pastes. Dried formulations based upon 3% Miragel® entrapped 88% trifluralin, 96% 2,4-D ester, 75% alachlor, and 9% butylate. Butylate retention increased to 42% with 6% Miragel® that had been pyrolyzed 1 h at 200° C. Release of trifluralin from Miragel® in the presence of αamylase solution increased with decreasing particle size and increasing level of active ingredient.