An evaluation of weed abundance and community diversity in response to pendimethalin application and manual hoe weeding in cowpea.

Abstract

The authors examined the impact of different rates of pendimethalin and its potency over manual weeding on weed species composition, density and diversity in cowpea, in a field experiment that had pendimethalin rates at (0.5, 1.5, 2.5, 3.5 kg a.i ha-1 followed by supplementary hoe weeding (SHW) at 42 days after sowing (DAS), 2 hoe weeding at 21 and 42 DAS and untreated weedy control; in Minna, Nigeria. The treatments were arranged in a randomized complete block design and replicated three times in each year of the study. The results showed that with increase in pendimethalin application, weed taxa density decreased and was lowest in the application of 2.5 kg a.i ha-1 pendimethalin + 1 SHW at 42 DAS. Weed species belonging to the Asteraceae, Papilionioideae, Poaceae, Onagraceae, Cyperaceae, Commelinaceae and some unidentified minor broad leaves dominated the weed community, as their presence could not be inhibited by pendimenthalin nor manual weeding. The lowest weed community diversity in terms of evenness and richness occurred when pendimenthalin was applied at 3.5 kg a.i ha-1 + 1 SHW at 42 DAS. The eigen analysis also showed that the total variation in composition of the weed taxa were due to the first four components instead of twenty, which accounted for 96.5 % of the total variation in the weed community composition. The result suggests that pendimethalin application at higher rates had an effect on the weed community diversity in cowpea.