Field studies were conducted in 2012 and 2013 to evaluate weed and insect control efficacy with glyphosate at 1 230 g ai (active ingredient) ha–1 and the insecticides acephate (728 g ai ha–1), carbosulfan (135 g ai ha–1), endosulfan (683 g ai ha–1), imidacloprid (32 g ai ha–1), or lambda-cyhalothrin (23 g ai ha–1), as well as glyphosate tank-mixed with these insecticides. Four of the most common weeds in cotton, common purslane, false daisy, goosegrass, and lambsquarters, were manually sown in the cotton field and treated with glyphosate alone or in combination with insecticides. Glyphosate efficacy, based on visual estimates of control and weed fresh weight at 21 d after treatment (DAT), was unaffected by the addition of insecticides. Four weeds were controlled by 93–97% and 86–100% (visual rating) and reduced weed fresh biomass by 98–99% and 96–100% with glyphosate alone and its combination with insecticides, respectively. Addition of glyphosate to acephate improved cotton aphid control compared with acephate alone. However, addition of glyphosate to carbosulfan, endosulfan, imidacloprid, or lambda-cyhalothrin did not affect the aphid control when compared with the insecticide alone treatments. These results indicate that cotton producers could potentially integrate weed and insect management strategies by choosing suitable insecticide mixing partners with glyphosate, thereby reducing the application costs without sacrificing the efficacy of the glyphosate or the insecticides.

Goosegrass is one of the worst agricultural weeds on a worldwide basis. Understanding of its interference impact in crop field will provide useful information for weed control programs. Field experiments were conducted during 2010–2012 to determine the influence of goosegrass density on cotton growth at the weed densities of 0, 0.125, 0.25, 0.5, 1, 2, and 4 plants m–1 of row. Seed cotton yield tended to decrease with the increase in weed density, and goosegrass at a density of 4 plants m–1 of row significantly reduced cotton yields by 20 to 27%. A density of 11.6–19.2 goosegrass plant m–1 of row would result in a 50% cotton yield loss from the maximum yield according to the hyperbolic decay regression model. Boll production was not affected in the early growing season. But boll numbers per plant were reduced about 25% at the density of 4 plants m–1 of row in the late growing season. Both cotton boll weight and seed numbers per boll were significantly reduced (8%) at 4 goosegrass plants m–1 of row. Cotton plant height, stem diameter and sympodial branch number were not affected as much as cotton yields by goosegrass competition. Seed index, lint percentage and lint fiber properties were unaffected by weed competition. Intraspecific competition resulted in density-dependent effects on weed biomass per plant, 142–387 g dry weight by harvest. Goosegrass biomass m–2 tended to increase with increasing weed density as indicated by a quadratic response. The adverse impact of goosegrass on cotton yield identified in this study has indicated the need of effective goosegrass management.