Controle de plantas daninhas com herbicidas e efeitos da seletividade destes sobre o crescimento e produtividade de feijão-caupi (Vigna unguiculata (l.) walp.)

Abstract

Three experiments were installed to evaluate the weed control with herbicides and the effects of these on growth and yield of cowpea (Vigna unguiculata (L.) Walp.). The first experiment was installed in the floodplain area that evaluated the weed control with eights herbicides: bentazon (720 g ha-1), clethodim (108 g ha-1), fluazifop-p-butyl (250 g ha-1), fomesafen (250 g ha-1), linuron (1490 g ha- 1), oxyfluorfen (960 g ha-1), s-metolachlor (1200 g ha-1) and sulfentrazone (600 g ha-1). The second and third experiments were installed in upland and had the objective of evaluating the efficacy and selectivity of herbicides: bentazon (0, 180, 360, 720, 1440 and 2880 g ha-1), fomesafen (0, 62, 5, 125, 250, 500 and 1000 g ha-1), fluazifop-p-butyl (0, 62.5, 125, 250, 500 and 1000 g ha-1) and clethodim (0, 27, 54, 108, 216 and 432 g ha-1) in cowpea crop and evaluated the effect of herbicides: bentazon (0, 180, 360, 720, 1440 and 2880 g ha-1), fomesafen (0, 62.5, 125, 250, 500 and 1000 g ha-1) and clethodim (0, 27, 54, 108, 216 and 432 g ha-1) on the growth of the culture. In the floodplain area the herbicides bentazon, clethodim, fluazifop-p-butyl, linuron, oxyfluorfen and sulfentrazone reduced more than 50% of the weeds. The cowpea tolerate the herbicides s-metolachlor, bentazon, fluazifop-p-butyl, clethodim, sulfentrazone and fomesafen. However, it was not tolerant to linuron and oxyfluorfen. The highest yields were obtained with bentazon, s-metolachlor and sulfentrazone. In the second experiment the herbicides bentazon and fomesafen reduced more than 50% of the dry matter of weeds. The fluazifop-p-butyl and clethodim were not effective in controlling weeds. The cowpea was tolerant to herbicides bentazon, fluazifop-p-butyl and clethodim and was susceptible to fomesafen. The best yields were obtained with the rates 360; 62.5; 125 and 108 g ha-1 of fomesafen, bentazon, fluazifop-p-butyl and clethodim, respectively. In evaluating the growth characteristics of cowpea, the herbicides bentazon (1440 g ha-1) and clethodim (432 g ha-1) were responsible for the lower production of leaf area, dry matter of aerial parts and leaf area index. The relative growth rate, net assimilation rate and leaf area ratio of cowpea treated with bentazon and clethodim had maximum growth at 7. The fomesafen caused the reduction in leaf area, dry matter of aerial parts and leaf area index of plants.