Interactions between rate, spray interval and number of applications of the synthetic pyrethroid Decis in cow pea (Vigna unguiculata) pest control

SUMMARYThe 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 25·0g a.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 contro l 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 × 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 × 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.An analysis of cost–benefit of the trial showed that 12·5 g a.i./ha gave higher returns than 25 g, as did two applications than three, but the trend in the spray interval was less consistent.

Yield Comparison of Four Forage Grasses at Two Cutting Heights and Three Harvest Intervals

Four forage grasses, i.e., Pangola, Digitaria decumbens Stent; Tanner, Brachiaria mutica; a Bermuda selection, Cynodon dactylon var. coursii and Hexapangola, Digitaria decumbens Stent, were evaluated under cutting management at the Corozal Substation located in the humid mountainous region of Puerto Rico. The effects of cutting heights of 2 and 6 inches above the ground, and of 30-, 45- and 60-day harvesting intervals were determined over a 2-year period. All grasses received 2 tons of 15-5-10 fertilizer per acre per year. At all cutting heights and harvest intervals, Bermuda (Cynodon dactylon var. coursii) had the highest dry forage yields while Pangola and Hexapangola had the highest crude protein contents. At all harvest intervals the grasses produced more total yields and crude protein per acre yearly when cut to a height of 2 inches than when cut to 6 inches above the ground. Green and dry forage yields produced by the grasses increased and on the average, crude protein content of the grasses decreased with the length of the harvest interval. A significant variety X cutting interval interaction was observed for total dry forage yields. Lower yields were obtained during the dry winter months at all cutting intervals. When cut 2 inches above the ground and every 60 days, Bermuda (Cynodon dactylon var. coursii) produced 28,247 pounds of dry forage per acre yearly containing about 9.0 percent crude protein.