Crop competitive ability contributes to herbicide performance in sweet corn

Crop variety effects on herbicide performance is not well characterised, particularly for sweet corn, a crop that varies greatly among hybrids in competitive ability with weeds. Field studies were used to determine the effects of crop competitive ability on season-long herbicide performance in sweet corn. Two sethoxydim-tolerant sweet corn hybrids were grown in the presence of Panicum miliaceum and plots were treated post-emergence with a range of sethoxydim doses. Significant differences in height, leaf area index and intercepted light were observed between hybrids near anthesis. Across a range of sub-lethal herbicide doses, the denser canopy hybrid Rocker suppressed P. miliaceum shoot biomass and fecundity to a greater extent than the hybrid Cahill. Yield of sweet corn improved to the level of the weed-free control with increasing sethoxydim dose. The indirect effect of herbicide dose on crop yield, mediated through P. miliaceum biomass reduction, was significant for all of the Cahill's yield traits but not Rocker. These results indicate that a less competitive hybrid requires relatively more weed suppression by the herbicide to not only reduce weed growth and seed production, but also to maintain yield. Sweet corn competitive ability consistently influences season-long herbicide performance.