Due to known variation in canopy properties among sweet corn hybrids, weed suppressive ability (WSA), the crop's ability to reduce weed fitness, may not be uniform among hybrids. This hypothesis was tested using a range of wild proso millet densities subjected to four canopy treatments (three hybrids weedy monoculture) under irrigated conditions in Washington and primarily rainfed conditions in Illinois. Parameter estimates for responses of weed growth and seed rain to wild proso millet density were used to quantify variation in WSA among hybrids. The same parameter estimates were used in a correlation analysis to identify associations between weed response and sweet corn canopy properties. Weed suppressive ability, as measured by wild proso millet shoot biomass and seed rain, varied among canopy treatments. Hybrid GH2547 was 25 to 31% more suppressive of wild proso millet than hybrid Spirit in Washington and 70 to 91% more suppressive in Illinois. Weed fitness was negatively correlated with leaf area index (LAI) after crop anthesis (−0.48 to −0.63), intercepted photosynthetically active radiation (PAR) at one of two harvest times (−0.51 to −0.56), and LAI at the 120- to 150-cm height (−0.51 to −0.55). Information on WSA may be useful in breeding programs; however, even near-term use of this knowledge offers modest but cumulative improvements to weed management systems in sweet corn.

Nomenclature: Wild proso millet, Panicum miliaceum L. PANMI, sweet corn, Zea mays L. ‘GH2547,’ ‘Spirit,’ ‘WHT2801.’