Evaluation of Pre-Emergence Herbicides for Weed Control in Cowpea (Vigna unguiculata (L.) Walp.) in a Forest - Savanna Transition Zone

Aims: To evaluate the efficacy and economic benefits of selected pre-emergence herbicides for weed control in cowpea.

Study Design: Randomized complete block design with four replications was used.

Place and Duration of Study: Research and Teaching Farm of Ambrose Alli University in Ekpoma (Lat. 6º 45’N, Long. 6º 8’E), in a forest-savanna transition zone of Nigeria, between August and December 2005 and August and December 2006.

Methodology: Five weed control treatments evaluated against unweeded control were; Codal gold(R) (250g prometryne + 162.5 g metolachlor per litre) at a rate of 1.65 kg a.i ha-1, Galex(R) (Metolachlor 250g + metobromuron 250g per litre) at the rate of 3.0 kg a.1.ha-1; Pendilin(R) (Pendimethalin 500g per litre) at a rate of 2.0 kg a.i ha-1, one hoe – weeding at 3 weeks after planting (WAP) and two hoe weeding at 3 and 7 WAP.

Results: Herbicides treatments and hoe weeded twice gave an acceptable (³70%) weed control in both years. Cowpea yield was best under Codal gold at 1.65 kg a.i ha-1 (with an average yield of ≥ 1600kg ha-1) while the unweeded control had the poorest yield (between 800 and 900 kg ha-1) in both years. The highest profit was obtained under Codal gold at 1.65 kg a.i ha-1 and the lowest in plot hoe weeded twice. The highest cost benefit ratio (CBR) of 24.61 in 2005 and 28.21 in 2006 were recorded with Codal goldR treated plot while the lowest of 1.25 and 1.22 were obtained in 2005 and 2006 respectively under plot hoe weeded twice.

Conclusion: Codal gold(R) at 1.65 kg a.i ha-1 was better than the other herbicides tried, in reducing weed infestation in cowpea as evidenced on the performance, yield of cowpea and higher economic returns. With the range of herbicides tried in this study, Codal gold(R) at 1.65 kg a.i ha-1 appears to be the best herbicide for weed control in cowpea under the present study