Influence of shattercane [Sorghum bicolor (L.) Moench.] interference on corn (Zea mays L.) yield and nitrogen accumulation

Field experiments were conducted to determine the effect of shattercane interference on corn grain yield and nitrogen uptake in central Missouri. A glyphosate-resistant corn variety was planted, and atrazine was used to control all weeds except shattercane. Glyphosate was applied when shattercane was 8, 15, 23, 31, 38, or 46 cm tall, and plots were hand weeded weekly thereafter. Season-long shattercane interference resulted in an 85% yield loss in 1999 and a 43% yield loss in 2000. Yield reductions occurred when shattercane was allowed to remain with corn until it was 31 cm tall. In both years, late-season corn biomass N content was highly correlated (r 0.95 and 0.84, respectively) with corn yield. When shattercane was allowed to reach the maximum recommended height for nicosulfuron or primisulfuron application (31 cm), significant yield losses occurred, and shattercane accumulated 10 and 20 kg N/ha, whereas corn accumulated 10 and 16 kg N/ha, respectively, in 1999 and 2000. Corn grain yield was reduced 0.66% (r(2) = 0.71) for each day of interference before a postemergence (POST) application of glyphosate.