Microencapsulated Alachlor and Its Behavior on Wheat (Triticum aestivum) Straw

Abstract

Scanning electron microscopy (SEM) was used to study alachlor microcapsule morphology and the effects of straw age and moisture on herbicide release. Microcapsule diameter in the formulation ranged from 2 to 15 μm. The polyurea encapsulating material was stable in water over time. Diffusion was suggested as the primary mode of alachlor release, with diffusion rate controlled by herbicide and salt concentration gradients between the microcapsule and the surrounding aqueous solution. Alachlor release was promoted by drying the microcapsules before addition to water. Microcapsule morphology was unchanged 48 h after application to dry straw, and microcapsules did not appear to adhere to the straw surface. Microcapsules applied to overwintered wet straw were shriveled at 48 h after treatment, indicating herbicide loss. Capsule walls were broken and appeared brittle after application to fresh wet straw. Organic constituents of the fresh straw cuticle may affect capsule wall integrity.