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Field experiments were conducted between 1994 and 1997 at the University of Ilorin Teaching and Research Farm, Ilorin (8o29`N; 4o35`E), in the southern Guinea savanna agro-ecological zone, to evaluate the efficacy of pre-emergence applications of two imidazolinone-based herbicide mixtures in cowpea (Vigna unguiculata) fields. Different rates of imazethapyr [(±)2-[4,5 dihydro-4-methyl-4-(1-methylethyl)-5-oxo-IH-imidazol-2-yl]5-ethyl-3 pyridine carboxylic acid] +pendimethalin (N-(1-ethylpropyl)-3,4dimethyl-2,6 dinitrobenzenamine)[Pursuit Plus]1 and imazaquin [2,[4,5-dihydro-4-methyl-4(1-methylethyl)-5-oxo-1H-imidazol-2-yl]3-quinoline carboxylic acid] + pendimethalin [Squadron]2 were compared with weedy or hand weeded control treatments, as well as with one or two rates of metolachlor [2-chloro-N-(2-ethyl –6-methylphenyl)-N-(2-methoxy-1-1 methyethyl) acetamide] + metobromuron[NI-(4- bromophenyl)N-methoxy-N-methylurea] (Galex)3, a standard herbicide recommendation for the crop. Each of the trials was designed as a randomized complete block with three or four replications. Results showed that various rates of the herbicide mixtures effectively controlled weeds in cowpea fields for between 6 and 10 weeks after planting (wap). Pursuit plus was generally more effective than Squadron at comparable rates of application, just as the tank mixtures of imazaquin+ pendimethalin were more effective than their formulated mixture (Squadron) at equivalent rates in the final trial. There was a significant positive correlation between weed control rating (wcr) and cowpea grain yield. The overall best treatment with regard to weed control and grain yield was Pursuit plus at 0.99 kg ai/ha, while the best rate of Squadron, based on the same criteria, was 1.02 kg ai/ha. Uncontrolled weed growth resulted in 45-59% reductions in grain yield. None of the herbicide mixtures was able to effectively control Vernonia galamensis and Paspalum orbiculare, while only Pursuit plus and a relatively high rate of Squadron (1.54 kg ai/ha) effectively controlled Tridax procumbens.
Keywords: dinitroaniline, imidazolinone, weed control rating, Vernonia galamensis, Paspalum orbiculare, Tridax procumbens
JARD Vol. 4 (2) 2005: pp. 104-121