EFFECTS OF RAIN-FREE INTERVALS AND HERBICIDE RATE ON SICKLEPOD (CASSIA-OBTUSIFOLIA) CONTROL AND ABSORPTION WITH AC-263,222

Experiments were conducted to evaluate the effect of a 2.5-cm simulate d rainfall 0.05, 0.25, 0.5, 1, 3, 6, and 24 h after POST applications of AC 263,222 to sicklepod. Fresh weight reductions were directly rela ted to increasing AC 263,222 rates and rain-free intervals. Fresh weig ht reductions with 9, 18, 36, 54, and 72 g ai/ha AC 263,222 were 32, 4 7, 55, 59, and 67%, respectively, with the rain-free treatment. A simu lated rainfall 0.05 h after POST application lowered fresh weight redu ctions with 9, 18, 36, 54, and 72 g/ha AC 263,222 to 5, 7, 19, 23, and 28%, respectively, of the untreated control. As AC 263,222 rates incr eased, a simulated rainfall shortly after POST application was less de trimental. At 18 g/ha of AC 263,222, a 3-h rain-free interval was nece ssary for fresh weight reductions equivalent to the rain-free control. As the rate of AC 263,222 increased to 54 g/ha, the rain-free interva l for fresh weight reductions equivalent to the rain-free control was reduced to 1 h. Radiolabeled studies indicated that at 3 h after appli cation an equivalent amount of C-14 was accumulated in the plant as co mpared with the rain-free control. The correlation coefficients for fr esh weight reductions and C-14 in the plant were r = 0.53, 0.75, 0.68, 0.74, and 0.70 at rates of 9, 18, 36, 54, and 72 g/ha AC 263,222, res pectively. Nomenclature: AC 263,222, xo-1H-imidazol-2-yl]-5-methyl-3-p yridinecarboxylic acid; sicklepod, Cassia obtusifolia L. #3 CASOB.