Pests of cowpea and their control in Northern Nigeria

Extract

Crops of cowpea (Vigna unguiculata) in Northern Nigeria are normally subject to such heavy attack by insects that the potential yields are seldom realised. The most important pests are Maruca testulalis (Geyer), which damages flowers and pods, Piezotrachelus varium (Wagn.), which attacks seeds, and the Coreids Acanthomia brevirostris Stål, A. horrida (Germ.), Anoplocnemis curvipes (F.) and Mirperus jaculus (Thnb.), all of which destroy pods. Pests that attack the pre-flowering stages of the cowpea are economically less important. Field surveys showed that, in 1961, Maruca testulalis, P. varium and Coreids together destroyed 62, 92 and 19 per cent, of the potential crop of seed from sowings in June, July and August, respectively. The corresponding percentages for 1962 were 55, 75 and 29, respectively.

The effectiveness of insecticides in the control of the pests that attack after flowering has commenced was investigated in field trials at Samaru, Northern Nigeria, in 1961–63. The results showed that large increases in yield could be obtained by spray treatments starting at the first appearance of the flowers. The best of these, consisting of 1 lb. DDT with 0·1 lb. BHC per acre applied six times at weekly intervals, gave an average yield over the five trials of 1,623 lb. dry seed per acre, which is a substantial increase over the estimated national average of 158 lb. per acre. Three applications of DDT/BHC, and six or three applications of Sevin at 1 lb. per acre, gave poorer results on the whole. Insecticidal treatment reduced the incidence of all pests and led to a corresponding reduction in flower losses. It also compressed the flowering period, induced earlier flowering and pod production, and caused the bulk of the crop to mature at one time. Haulm production was also reduced, and crops grown for haulms rather than for seed should therefore not be treated with insecticides.