Biocontrol of pests of vegetable cowpea (Vigna unguiculata sub sp. sesquipedalis (L.) verdcourt)

Abstract

Monitoring of the incidence of pests and their natural enemies was carried out in the heavily insecticide sprayed vegetable cowpea plots in farmers' fields in two locations viz. Kalliyoor and Palappur in Thiruvananthapuram District and in the unsprayed crop raised in the Instructional Farm, College of Agriculture, Vellayani, during kharif and rabi, 1996. The results of the monitoring revealed that the pea aphid, A. craccivora , the pod bugs R. pedestris and C. gibbosa and the pod borers H. armigera, L. boeticus and M. testulalis were the major pests that attacked vegetable cowpea both in the insecticide sprayed as well as in the unsprayed plots. The pea aphid was persistent in the insecticide sprayed fields where as in the unsprayed fields, they were not seen upto 35 days after sowing, in both kharif and rabi season. The pod bugs and pod borers were seen throughout the cropping period with increase in the post flowering period in both sprayed and unsprayed crop. Attack of the american serpentine leaf miner L. trifolii was observed only in the insecticide sprayed fields and was present in rabi as well as in the kharif seasons

The

parasitoids that

were

encountered

were

A. nigrotibiali$, Charops sp., Salius sp. and T. subvirescens

and the predators were M. sexmaculatus, M. crocea, Scyanus sp., E. stali, S. geminate and X. scutellarae. The population of the natural enemies was higher during the rabi season than that during kharif season. The population of the pests and natural enemies in the insecticide sprayed and unsprayed plots were compared using students ‘t' test and the results revealed that the pest were more in the un sprayed plots but the population was higher only for a shorter period and it was effectively checked by the natural enemies, the population of which synchronized with that of the pests. There was significantly higher population of natural enemies in the unsprayed plots when compared to unsprayed plots. The role of the green lacewing C. carnea in the management of the vegetable cowpea pests was studied through replicated field trials conducted at College of Agriculture, Vellayani during 1996. The impact of biorationals viz., neem oil and tobacco decoction and insecticide, malathion on the predator C. carnea and in their effectiveness in management of cowpea pests was also studied in the field experiment. C. carnea released @ 50 per plot at fortnightly intervals effectively checked the aphid population. Among the botanicals, tobacco decoction 2 per cent was found to be effective in controlling the aphids, pod bugs and pod borers.

Neem oil emulsion 10 per cent when applied at fortnightly intervals was also found to be significantly superior to the untreated control. However the infestation by aphids and the pod bugs was' less in all the treatments when compared to control. Though the control plot did not show significant reduction in yield, the quality of the produce was reduced due to the pest infestation. C. carnea @ 100 per plot at fortnightly and monthly intervals were effective against pod bugs. The pod borers were effectively checked by C. carnea • 50 arid 100 per plot. In general the monthly release of C. carnea was comparatively less effective in controlling the pests. The botanicals did not show any deleterious effect on C. carnea. When the yield was assessed in terms of weight and number of pods harvested, significantly higher yield was recorded only in plots treated with tobacco decoction 2 per cent when compared to untreated control.