IMPROVING SOYBEAN (GLYCINE-MAX) TOLERANCE TO AC-263,222 BY LIMITING TERMINAL EXPOSURE

Field experiments were established to evaluate the effects of various band widths left open directly over the soybean row to improve soybean tolerance to AC 263,222 and chlorimuron applied POST, while maintaini ng weed control. Drop tubes with even fan tips extended below the spra y boom to within 40 and 30 cm from the ground to obtain 5 and 10 cm op en bands at the soybean terminals. AC 263,222 applied broadcast at 13, 18, and 36 g ai ha-1 injured soybean 14, 16, and 32%, respectively, 3 DAT. AC 263,222 at 36 g ha-1 applied with a 5-cm and 10-cm open band injured soybean 11 and 3%, respectively. Chlorimuron injury was 12% or less for all treatments. Metribuzin followed by AC 263,222 or chlorim uron was not more injurious to soybean than AC 263,222 or chlorimuron alone. Metribuzin PRE followed by 36 g ha-1 AC 263,222 applied in a 10 -cm open band controlled sicklepod and pitted morningglory 86 and 92%, respectively, 6 WAT. Sicklepod control was similar with open-band tre atments compared to the same rate applied broadcast; however, 18 g ha- 1 AC 263,222 applied in a 10-cm open band provided less pitted morning glory control than the broadcast treatment. Soybean treated with herbi cides in a band produced yields similar to or greater than soybean tre ated with the same herbicides broadcast. Metribuzin followed by 36 g h a-1 AC 263,222 with a 10-cm open band resulted in a soybean yield of 2 840 kg ha-1, which was greater than any other herbicide treatment and equivalent to the weed-free check. Nomenclature: AC 263,222, oxo-1H-im idazol-2-yl]-5-methyl3-pyridinecarboxylic acid; chlorimuron, yrimidiny l)amino]-carbonyl]amino]-sulfonyl]benzoic acid; metribuzin, thylethyl) -3-(methylthio)-1,2,4-triazin-5(4H)-one; pitted morningglory, Ipomoea lacunosa L. #3 IPOLA; sicklepod, Cassia obtusifolia L. # CASOB; soybea n, Glycine max (L.) Merr. 'Terra-Vig 5452.'