Technical Abstract: 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. Variation in hybrid suppression of wild proso millet was evaluated by comparing among canopy treatments the coefficients of regressions of weed growth and seed rain on wild proso millet seedling density. The same coefficients 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 after crop anthesis (-0.48 to -0.63), intercepted photosynthetically active radiation at one of two harvest times (-0.51 to -0.56), and leaf area index 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.