Effects of Rainfall and Temperature on Postemergence Control of Sicklepod (Cassia obtusifolia) with Imazaquin and DPX-F6025

Foliar absorption of imazaquin {ammonium salt of 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} following postemergence application was not necessary for control of sicklepod (Cassia obtusifoliaL. # CASOB). Application of imazaquin to the soil resulted in control similar to application to the soil plus foliage. A 0.6-cm simulated rainfall 0.05 h after postemergence application of 140, 280, or 560 g ae/ha of imazaquin did not reduce sicklepod control. Foliar absorption was necessary for control with postemergence application of DPX-F6025 {ethyl ester of 2-[[[[(4-chloro-6-methoxypyrimidin-2-yl)amino]-carbonyl] amino] sulfonyl] benzoate}. Application of DPX-F6025 to the foliage resulted in control similar to application to the soil plus foliage. Sicklepod control resulting from postemergence application of 18 g ae/ha of DPX-F6025 was reduced when 0.6 cm of simulated rainfall was received 1 h after application but not when received 4 h after application. With application of 9 g/ha of DPX-F6025, simulated rainfall 24 h after application reduced control. Sicklepod control resulting from postemergence application of sublethal rates of imazaquin and DPX-F6025 was greater when plants were exposed to 3 or more days of 24/18 C day/night temperature than when grown at a continuous 32/24 C temperature. Exposure to low temperature for 3 days immediately before imazaquin application resulted in greater enhancement of control than did exposure for 3 days immediately after application. The reverse was found with DPX-F6025. Control obtained with both imazaquin and DPX-F6025 increased as the number of days of exposure to low temperature increased from 3 to 6. Enhancement of control with low temperature diminished as the herbicide application rate increased.