Effect of Tillage Timing on Herbicide Toxicity to Field Bindweed

Abstract

When can tillage be resumed after herbicide treatment of field bindweed (Convolvulus arvensis L.) without reducing control ? This question was answered with experiments on a clay loam soil in the semi-arid southern Great Plains in mid-summers of 1979, 1985, and 1986 when field bindweed vigor was visually rated as good, fair, or poor, respectively. Plant vigor was controlled by availability of soil water. Highest control, about 95%, of field bindweed 9 mo after application of 2,4-D, glyphosate, and dicamba was aehieved when vigor was good. Control with picloram + 2,4-D was not affected by plant vigor. When field bindweed growth was rated as good, control with dicamba, glyphosate, and a mixture of 2,4-D and picloram was not reduced when sweep tillage was delayed for 1 day after treatment (DAT). To achieve maximum control with 2,4-D, tillage had to be delayed 7 DAT. When plant vigor was fair, control was not reduced with picloram + 2,4-D when tillage was delayed 2 DAT. Glyphosate and dicamba gave maximum control after 3 DAT delay, and 2,4-D required a 7 DAT delay for maximum effectiveness. With poor plant vigor, picloram + 2,4-D, a herbicide combination that persisted in the soil, gave best control when tillage was delayed 2 DAT. Dicamba, a less persistent herbicide, required a 7 DAT delay for maximum controL Control was not better than zero 9 mo after treatment with glyphosate or 2,4-D when plants had poor vigor.