Comparison of Graminicides Applied at Equivalent Costs in Soybean (Glycine max)

Abstract

Eleven field experiments were conducted during 1994 and 1995 to compare rhizomatous johnsongrass control and soybean yield with single POST applications of quizalofop-P, fluazifop-P, clethodim, and sethoxydim at costs of $9.88, 19.76, 29.64, and 39.52/ha for each graminicide. Cost of the manufacturer's suggested use rate for these graminicides was approximately $29.64/ha, which corresponded to 0.09, 0.22, 0.14, and 0.27 kg ai/ha for these respective graminicides. When applied at a cost of $9.88/ha, quizalofop-P controlled rhizomatous johnsongrass more effectively than the other graminicides in five of 11 experiments. Quizalofop-P and fluazifop-P controlled johnsongrass similarly when applied at higher costs per hectare in 10 of 11 experiments. Sethoxydim was less effective than quizalofop-P or fluazifop-P in most instances, especially when graminicides were applied at costs of $9.88 or $19.76/ha. Clethodim was generally more effective than sethoxydim. Fluazifop-P and clethodim controlled rhizomatous johnsongrass similarly in six of 11 experiments regardless of cost. Differences in rhizomatous johnsongrass control among graminicides did not always translate into differences in soybean yield, although graminicides increased yield over the nontreated control in most experiments regardless of the graminicide cost. In several experiments, soybean treated with clethodim or sethoxydim applied at a cost of $9.88/ha yielded lower than when applied at higher costs.