COMPARISON OF GRAMINICIDES APPLIED AT EQUIVALENT COSTS IN SOYBEAN (GLYCINE-MAX)

Eleven field experiments were conducted during 1994 and 1995 to compar e rhizomatous johnsongrass control and soybean yield with single POST applications of quizalofop-P, fluazifop-P, clethodim, and sethoxydim a t costs of $9.88, 19.76, 29.64, and 39.52/ha for each graminicide. Cos t 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 ef fectively than the other graminicides in live of Il experiments, Quiza lofop-P and fluazifop-P controlled johnsongrass similarly when applied at higher costs per hectare in 10 of 11 experiments. Sethoxydim was l ess effective than quizalofop-P or fluazifop-P in most instances, espe cially when graminicides were applied at costs of $9.88 or $19.76/ha. Clethodim was generally more effective than sethoxydim. Fluazifop-P an d clethodim controlled rhizomatous johnsongrass similarly in six of 11 experiments regardless of cost, Differences in rhizomatous johnsongra ss control among graminicides did not always translate into difference s in soybean yield, although graminicides increased yield over the non treated 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 high er costs.