In field trials made in 1977, the synthetic pyrethroids Deois and Permethrin offered better protection to cowpea flowers and pods but the crop did not outyield that treated with Nuvacron in grain production. Further evaluation of Decis and Permethrin in 1978 showed that the relationships between rate and insect damage, and yield were curvilinear. On the early crop, Decis at 15 g a.i./ha and lOga.i./ha reduced insect damage to flowers and pods, respectively, below the control but yield differences were not significant from 5 to 50 g. Four or five applications of Decis were most effective in reducing insect damage, but yields obtained from them were not better than that from one application. Permethrin at 12-5 g a.i./ha reduced insect damage below the control but produced grain yield which was significantly lower than 25 g and above.On the late crop, Permethrin was effective from 5 to 25 g in reducing insect damage and providing increased grain yield. One application of Decis was sufficient to reduce pod damage and increase grain yield over the control, but appreciable yields were obtained from the three and four application regimes.A cost/benefit analysis of insecticide application shows that the synthetic pyrethroids compared favourably with Nuvacron. In 1978, two and three applications of Decis gave the highest net returns on the early and late season crops, respectively. Decis appeared most economical at 10 g on the early crop while Permethrin was most rewarding at 62-5 g in the early crop and 10 g in the late crop. The seasonal differences in weather are discussed in relation to the performance of the crop.
The relationship between rate, spray interval and number of applications of Decis for pest control in cow pea was investigated. In 1978 and 1979, neither the rates nor the interaction effects were significant in grain yield when 12-5 and 25-0ga.i./ha of Decis were applied three times weekly or twice at intervals of 10 or 14 days.Further trials in 1980 showed that for the control of thrips (M. sjostedti), rate, interval and number of applications were significant for samples at 49 days after planting and beyond, suggesting that the residual life of Decis is about 10 days. Three applications were significantly better than two for lowering the population of C. tomentosicollis and the number x interval interaction was also significant. The number, rate and interval were significant without interaction effects for shrivelled pods caused by all hemipteran pests. In all the trials in 1980 and 1981, damage by the pod borer M. testulalis was low. Rate and number x interval interaction were generally significant but no differences were observed in grain yield. However, in 1980 the higher rate and three applications gave better quality crop, resulting from less hemipteran damage.
The effect of one, two or three applications of monocrotophos at 1120 g ai/ha at weekly intervals was determined on cowpea var. Ife Brown. All regimes were equally effective in grain production in early 1974 but spray applications 35 and 42 days after planting gave the best result in the late crop. Grain production from two applications was not significantly different from three applications in 1975. The control plots in the late season of both years failed, due to moisture stress and lack of pest control measures. It is considered that two sprays at flowering is adequate to forestall a crop failure in this variety.Chemical methods are the only ones employed at present for the control of insect pests of cowpea in Nigeria, particularly those infesting the flowers and pods. The pod borer complex of cowpea, of which Maruca testulalis Geyer is the most important, also includes Cydia ptychora Meyrick, Virachola antalus Hopkins and Heliothis armigera Hubner.In order to minimize hazards due to the use of excessive amounts of insecticide, breeders and entomologists are actively engaged in research to produce varieties which combine insect resistance with the qualities of grain preferred by consumers. However, until the advent of such varieties it is expedient to combine other pest management practices, as was suggested by Taylor (1965) for C. ptychora, with minimum but effective insecticide spray schedules that can be based on a reduction in the frequency or rate of application, or both.Field tests with insecticides at Moor Plantation currently consist of one weekly application of insecticide at 1120 g ai/ha, beginning 35-49 days after planting for early maturing varieties. This paper attempts to evaluate the effect of one, two or three sprays applied at weekly intervals with a view to reducing the present frequency of applying monocrotophos on the performance of cowpea Ife Brown, which is a semi-erect, early maturing, determinate variety producing an acceptable grain type.
MATERIALS AND METHODS
testsIfe Brown was planted 30 cm apart on ridges 60 cm apart, in 5-5 x 3-7 m plots, after broadcasting 22-6 kg N and 52-4kgP/ha before ridging. Plants were thinned to one plant/stand when fully established. The early crop was planted
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