Doctor of Philosophy, The Ohio State University, 2005, Horticulture and Crop Science

Studies were conducted at the plant, population, and community level to address questions concerning (1) seed germination in Alliaria petiolata (2) weed community composition and structure in response to tillage, rotation and herbicide, and (3) variation in Abutilon theophrasti. Alliaria petiolata seeds are dormant at maturity, requiring approximately 90 to 105 days cold-moist stratification at 4 to 5 °C for germination to occur. Mechanically scarified, and H2O2 and H2SO4 treated seeds germinated within 35 days when GA3 was applied exogenously. The composition of the weed-seedbank community was characterized 35 years after the implementation of a long-term study involving cropping sequence (continuous corn, corn-soybean, corn-oat-hay) and tillage system (conventional-, minimum-, and no-tillage). Values of S, J, and H' recorded for all combinations of the three-crop sequence were typically greater than the values of S, J, and H' reported for either the one and two-crop rotations. As the intensity of soil disturbance decreased, values for S increased. Mean germinable weed seed density was greatest in the no-tillage treatments across rotations and years. Results suggest that the weed seed community in a corn-oat-hay rotational system differs in structure and composition from communities associated with continuous corn and corn-soybean systems. There is concern that the widespread use of genetically-modified glyphosate-tolerant crops (GTCs) will alter agricultural weed community dynamics with respect to glyphosate-tolerance and emergence phenology. Species associated with individual tillage and rotation treatments were not different from species recorded in the same plots prior to the exclusive use of GTCs and glyphosate, suggesting that significant changes in weed community composition and structure have not occurred. Abutilon theophrasti is a noxious weed in modern row-crop agriculture. This study characterized the morphological, phonological, and genetic variation ve (open full item for complete abstract)

Committee: John Cardina (Advisor) Subjects: Agriculture, Agronomy