Efficacy of Candidate Herbicides for Post- Emergence Weed Control in Kenaf (Hibiscus cannabinus L.)

Post emergence application of herbicides reduced weed growth, enhanced kenaf agronomic traits and fibre yield. A study was conducted to determine the efficacy of some herbicide formulations for post emergence weed control in kenaf at Ibadan (0.7.38N; 003.84E- Derived savanna agro-ecology) station of the Institute of Agricultural Research and Training (IAR&T), Obafemi Awolowo University, Ibadan in 2016 and 2017 rainy seasons. Herbicides applied were Quazilofop-P-ethyl (100, 150, 200 ml/ha), Oxyfluorfen (0.96, 1.20 and 1.44 kg ai/ha) and Fluazifop-p-butyl 150, 225 and 300 g ai/ha) at three rates each, while weed-free and weedy were the control treatments. Weed flora composition before land preparation was dominated by annual weeds; broadleaves (70%), grass (20%) and spiderwort (10%). At 10 weeks after sowing (WAS), weed flora composition comprised of 64% broadleaf, 14% grass, 8% spiderwort and 14% sedge. Weed flora dynamics after treatments application might have been influenced by herbicide formulations applied. Oldenlandia corymbusa, Cyperus escunlentus, Desmodium scorpurus and Cyperus rotundus were identified as prevalent weeds across the treatments applied while Mimosa pudica, was a minor weed. Herbicides improved kenaf agronomic traits (plant height, stem-butt girth and number of leaves/plant) due to minimal weed competition; reduced weed flora composition and weed weight relative to weed infested kenaf plants in weedy control. Oxyfluorfen (0.96, 1.20 and 1.44 kg ai/ha); fluazilof-p-butyl (225 and 300 g ai/ha); Quazilofop-P-ethyl (100 and 200 ml/ha) reduced weed dry weight by 60-70%. Weed-free plots had the highest weed control efficiency (WCE %). Evidently, acceptable WCE of ≥ 80% and comparable gross fibre yield with the maximum in weed-free recorded in Oxyfluorfen (1.20 and 1.44 kg ai/ha) and Fluazilofop-p-butyl (300 g ai/ha) showed their efficacies. However, low WCE 50 -65% in Quazilofop-p-ethyl (100, 150, 200 ml/ha) might reflected a review of the doses applied for better efficacy. Kenaf gross fibre yield was reduced by 65% in the weedy check plot, due to superior weed infestation and utmost weed dry weight accumulation. Notwithstanding, the benefit-cost ratio and environmental impact assessment of the study must be carried out for economically viable kenaf production and environmental friendliness.