Isoparaffinic Oil as a Carrier for Chlorpropham and Terbacil

Abstract

The herbicides 3-tert-butyl-5-chloro-6-methyluracil (terbacil) and isopropyl m-chlorocarbanilate (chlorpropham) showed greatly enhanced activity on giant foxtail (Setaria faberii Herrm.) and ivyleaf morningglory (Ipomoea hederacea (L.) Jacq.) when applied in an isoparaffinic oil rather than water. The activity of terbacil was enhanced but to a lesser extent when crop oil was added to a water carrier at a concentration of 10%. In field trials, similar enhancement of terbacil and chlorpropham activity was obtained on several weeds. Onions (Allium cepa L., var. Spartan Gem) in the “loop stage” were moderately tolerant and carrots (Daucus carota L., var. Royal Chantenay) were highly tolerant to chlorpropham at 4 lb/A applied in the isoparaffinic oil. Peppermint (Mentha peperita L.) and spearmint (Mentha spicata L.) were tolerant to terbacil applied in the oil at rates sufficient to give good weed control. The oil alone had no injurious effects on onions, carrots, peppermint, or spearmint. This enhancement in activity in greenhouse and field studies appeared to be due to increased penetration as shown by washing, speed of killing plants, and tracer studies. Tracer studies showed that within 2 hr after application, the isoparaffinic oil increased the penetration of chlorpropham more than eightfold in ivyleaf morningglory and more than fourfold in giant foxtail compared to a water carrier. This increase in penetration was even more striking with terbacil. After 4 hr, penetration was increased over 16 times in ivyleaf morningglory and over 18 times in giant foxtail, when applied in the oil rather than acetone. Chlorpropham and terbacil were translocated to the shoot apex of ivyleaf morningglory only when they were applied in the oil.