Use of low dosage pendimethalin in combination with supplementary weeding in maize (zea mays L.) and bean (phaseolus vulgaris l.) intercrop.

Abstract

Field trials were designed to determine the effect of various weed control methods in maize. (Zea mays L.) and bean (Phaseolus vulgaris L.) intercrop. Pendimethalin herbicide was applied at three rates i.e. 1.5, 1.0 and 0.5 kg a.i./ha on maize and bean intercrop, to determine the degree of weed control and herbicide injury on the, crops. The two lower rates were combined with one supplementary weeding each, to determine weed control, reduction on weeding time and cost. Manual weed control methods were included to help compare the net monetary benefit of each weed control method. Other cropping systems namely sole maize and sole beans were studied to determine the effect of intercropping on weed control and crop yields. According to this study, intercropping maize and beans showed no consistent effect on weed suppression, although it yielded the lowest weed dry matter of the three cropping systems. Intercropping maize and beans suppressed bean yield by 486.3 kg/ha in the short rains and 735.7 kg/ha in the long rains, but in terms of monetary benefit, was the prefered cropping system. There were marked differ2nces between weed control treatments. Application of pendimethalin (viii) at 1.5 kg a.i./ha caused deformation and stunted growth on beans, often in localised spots. Both low rates, 0.5 kg a.i./ha and 1.0 kg a.i./ha, did not cause any herbicide injury on beans and did not control any of the prevalent weed species. Combined with one supplementary weeding each, however, they effected better weed control than pendimethalin alone at 1.5 kg a.i./ha. The two low rates; 0.5 kg a.i./ha and 1.0 kg/ ha combined with supplementary weeding reduced weeding time by 20.1, 21.3 man-days/ha in the short rains and 11.5, 15.2 man-days/ha in the long rains, respectively and achieved about the same degree of weed control :as two hand weedings. They further reduced cost of weed control by 15.2, 8.9 US$/ha in the short rains and 9.0, 1.3 US$/ha in the long rains compared to two hand weedings, but raised cost by 3.4, 9.7 US$/ha in the short rains and 8.4, 12.2 US$/ha in the long rains compared to chemical control with pendimethalin at 1.5 kg a.i./ha. Results were, however, not consistent in the two seasons,' suggesting a seasonal influence, particularly amount of rainfall received soon after application of herbicide. The use of low dosages of herbicide plus (ix) supplementary weeding compared vary favourably with two hand weedings, the cultural method of weed control, in net benefit. They both gave higher monetary benefit than both use of herbicide alone at normal rate i.e. 1.5 kg a.i./ha and a single hand weeding. Of the two low rates, 0.5 kg a.i./ha plus a supplementary weeding was to be prefered as it gave a higher net benefit. The use of low dosages of herbicide combined with a supplementary hand weeding in this study, as in other studies, provides an alternative method of weed control. It reduces labour requirement and cost of weed control, at the same time, gives a comparable net income to the cultural ITethod of weed control.