Mechanism of reaction of cowpea varieties to Alectra vogelii (Benth) and its control.
Field experiments were conducted in Nigeria to study the mechanism of reaction of cowpea cultivars to Alectra vogelii and how this impacts on the control of the parasitic plant. In the first trial, 18 cowpea cultivars were evaluated for resistance/tolerance to A. vogelii. The second trial was made up of 25 herbicide treatments compared to hoe-weeding at 3 and 6 weeks after sowing (WAS) and untreated control using cowpea cv. SAMPEA-7. The third trial used 3 cowpea cultivars (B301, TN93-80 and VITA-3) with 3 levels of N and P, respectively. The results showed that cultivar B301 and the derivatives of its crosses with IT84S-2246-4 (IT90K-59 and IT90K-76) did not support A. vogelii emergence, while SAMPEA-7 and TVX3236 supported high infestation with consequent high susceptibility to the parasite. Preemergence herbicide application of a mixture containing pree (metazachlor + antidote), followed by imazaquin at 0.18 kg a.i/ha resulted in significantly lower number of plants infected by the parasite. The highest level of N (60 kg N/ha) significantly reduced the number of plants infected by the parasite at harvest, while grain yield increased with P levels. This investigation showed that cultivar B301 and the derivative of its crosses with IT84S-2246-4 (IT90k-59 and IT90k-76) did not support the emergence of A. vogelii and thus exhibited resistance. Cowpea cv. VITA-3 had potential to tolerate A. vogelii, while higher dose of N (360 kg/ha) was detrimental to cowpea grain yield. Farmers can reduce cowpea infection by A. vogelii when preemergence herbicide mixtures containing pree (metazachlor + antidote) are applied, followed by post-emergence application of imazaquin at 0.18 kg a.i/ha.