Preparation of Starch Esters of Herbicides and Their Evaluation as Slow‐Release Agents

A number of starch esters of various herbicides were prepared from an activated pregelatinized starch and the acid chlorides of the respective herbicides. Picloram was released from aqueous suspensions of the ester, to which nonsterile soil was added, in sufficient amount to inhibit lettuce growth. Application of the suspensions to a sterile soil at a rate equivalent to 5 kg picloram/ha was phytotoxic to lettuce for at least three seedings over 48 days. Similar results were obtained by incorporating the solid herbicide ester directly into nonsterile soil. In nonsterile soil, pregelatinized starch picloram esters hydrolyze more readily than unmodified starch picloram esters.