Effect of nicosulfuron dosages and timing on the post emergence control of cogongrass (Imperata cylindrica) in corn (Zea mays)

Cogongrass is an aggressive perennial weed, which causes severe yield losses in major crops of the moist savanna of West Africa. Field studies were conducted from 2000 to 2002 at Alabata and Ilorin, Nigeria, to evaluate the influence of dosage and time of nicosulfuron application on the control of cogongrass and corn grain yield. Nicosulfuron dosages were 50, 100, 150, and 200 g ai/ha applied 1, 2, 3, or 4 wk after planting (WAP) corn. Hand-weeded and nonweeded treatments were the controls. Three to 4 wk after treatment and at final harvest, all plots that received nicosulfuron had significantly lower cogongrass shoot dry matter (DM) than the nonweeded control across locations in all years (P ≤ 0.01). Nicosulfuron increased corn grain yield at Alabata by 96% in 2000, 100% in 2001, and 34 to 54% in 2002, and at Ilorin by 79 to 83% in 2001 and 60 to 69% in 2002 when compared with the nonweeded control. The weeded control had corn grain yield similar to plots that received nicosulfuron at 200 g/ha at Alabata in 2001, 150 g/ha at Ilorin in 2001, 50 to 200 g/ha at Alabata in 2002, and 150 and 200 g/ha at Ilorin in 2002. There were negative linear relationships between corn DM, grain yield, and cogongrass shoot DM. Application of nicosulfuron at 1 or 2 WAP, when cogongrass was 22 to 27 cm tall, gave better grain yield and lower cogongrass shoot DM than at 3 or 4 WAP, when cogongrass was 36 to 45 cm tall. The study concludes that 150 to 200 g/ha of nicosulfuron applied at 1 or 2 WAP is effective for cogongrass control without adverse effect on corn grain yield