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The problems associated with short growing seasons has led to the development of leafy-reduced stature (LRS) corn hybrids. These hybrids have more leaf area above the ear, more rapid leaf area development, shorter stature, earlier maturity, and better responses to high plant populations and narrow spacings than conventional hybrids. Plants grown in a reduced light environment are limited in carbon assimilation and this, in turn, results in reductions in growth and development. A way to supplement the availability of photosynthate is injection of sucrose into plant stems. The objective of this thesis was to determine the ability of LRS corn plants to compete with weeds, and the reactions of weed species to the shade, including the relationships between weed growth (increase in biomass) and development (shape) under shaded conditions. Three years of field experiments (LRS and more conventional corn hybrids with both transplanted and naturally growing weeds) and two years of greenhouse work [weeds alone, C3 (lamb's quarters and velvetleaf) and C4 (redroot pigweed) in full sun or deep (75%) shade injected with 15% sucrose or not] were conducted. Yield reductions due to weed pressure were lower for LRS than other hybrids. Biomass production by both transplanted and naturally occurring weeds was up to 85% less under corn canopies than when grown without competition from corn. The biomass of C4 weeds was more reduced by competition with corn plants than that of C3 weeds. In spite of quick and early leaf development, leaves and other plant parts of LRS were not damaged excessively by mechanical (rotary hoeing) weed control. Both C3 and C4 weed plants produced more dry matter when injected with sucrose. Dry weights of sucrose injected shaded plants were not different from full sun uninjected plants. However, sucrose injection did not alter shading effects on development (distribution of biomass). Dry matter production and photosynthetic rates of C4 weeds were more reduced

The migration of waterhemp (Amaranthus tuberculatus) into northern sugarbeet (Beta vulgaris) growing regions has prompted sugarbeet producers to utilize inter-row cultivation in their weed management program as no currently registered herbicides can control glyphosate-resistant waterhemp postemergence. Field experiments were conducted to evaluate cultivation efficacy on waterhemp and common lambsquarters (Chenopodium album) and to evaluate cultivation safety on sugarbeet. Cultivation efficacy experiments demonstrated cultivation removes 65% of waterhemp and has no effect on further waterhemp emergence, but can be deleterious to common lambsquarters control if cultivation is timed before sugarbeet canopy closure. The ideal time to implement inter-row cultivation in sugarbeet is after sugarbeet canopy is closed and can suppress further weed emergence. Cultivation safety experiments demonstrated three cultivations as late as August 16 had no effect on sugarbeet yield and quality. Cultivation is a valuable tool to control glyphosate-resistant weeds with no deleterious effects if used correctly. / Sugarbeet Research and Education Board of Minnesota and North Dakota