Postemergence Combinations of Imazaquin or Imazethapyr by AC 263,222 for Weed Control in Soybean (Glycine max)

Abstract

Field experiments were established to evaluate weed control with AC 263,222 alone and in combination with imazaquin or imazethapyr. Addition of AC 263,222 to either imazaquin or imazethapyr resulted in additive or synergistic increases in control of johnsongrass, pitted morningglory, and entireleaf morningglory. Reducing the rate of imazaquin from 140 to 18 g ai ha−1did not reduce control of johnsongrass or pitted morningglory when AC 263,222 was added at 18 g ai ha−1and above, compared to 140 g ha−1imazaquin alone, through 8 weeks after treatment (WAT). When 9 g ha−1or more AC 263,222 was added to imazethapyr, reducing imazethapyr rate from 70 to 9 g ai ha−1did not reduce control of johnsongrass or pitted morningglory through 8 WAT. Adding 9 g ha−1or more AC 263,222 to various rates of imazaquin or imazethapyr 2 and 8 WAT additively or synergistically increased control of johnsongrass, pitted morningglory, entireleaf morningglory, and tall waterhemp compared to those herbicides applied alone. Soybean injury increased 2 WAT when 35 or 70 g ha−1AC 263,222 was added to most rates of imazaquin or imazethapyr, but was less than 15% in all treatments by 8 WAT. Visual soybean injury did not translate into a yield loss, and an increase in weed control often resulted in increased yield.