The toxicological effect of paraquat post emergence herbicide on growth characteristics of cowpea (<i>vigna unguiculata</i> (l.) Walp)

Abstract

The study was conducted to examine the effect of paraquat herbicide on growth characteristics of cowpea. The paraquat herbicide was applied at two rates; 0.50 and 1.00kg ai/ha. Information was obtained on the vegetative growth parameters of cowpea which included plant height, number of leaves, leaf area, phytotoxicity and weed control effectiveness of the herbicide. The results showed that there were significant differences (P< 0.05) in vegetative growth in cowpea plants when paraquat was used as post emergence herbicide for weed control. There was good growth and adequate weed control achieved by all herbicide treatments evaluated until 9 weeks after planting (WAP) before decline set in. However, cowpea plant heights were significantly higher (P<0.05) in plots treated with paraquat at 1.00kg ai/ha. Highest number of leaves was recorded during growth at 4 – 6 WAP with paraquat at 1.00kg ai/ha. The leaf area also showed significant difference (P<0.05) in plants treated with handweeded and paraquat herbicide at 0.50 and 1.00kg ai/ha. However, cowpea vegetative growth performance in herbicide treatments compared favourably with handweeded control plots and better than the unweeded control. Phytotoxicity symptoms to cowpea plants was high in paraquat treated plots at the rate of 1.00kg ai/ha than at 0.50kg ai/ha at 4 - 6 WAP. The highest plant height and leaf area were obtained from handweeded control plots while the unweeded plots gave the poorest growth parameters.