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Degree Name

Doctor of Philosophy




The germination, emergence and rates of growth of corn, giant foxtail and velvetleaf under different environmental and cultural conditions were evaluated. Germination studies were used to examine the influence of constant temperatures of 10, 20, and 25(DEGREES)C and alternating night/day temperatures of 15/25 and 20/30(DEGREES)C. Germination of corn and giant foxtail was reduced at 10(DEGREES)C. Velvetleaf germination was inhibited at 25(DEGREES)C but was not reduced at 10(DEGREES)C;Growth chamber studies were designed to investigate the effect of five temperature regimes on germination and seedling growth: day/night temperatures of 14/9, 24/9, 20/10, 25/15, and 35/25(DEGREES)C. The warmest temperature treatment, 35/25(DEGREES)C, was most favorable for early emergence and growth of all three species. Velvetleaf emerged before corn and giant foxtail with the colder temperature treatments of 14/9 and 24/9(DEGREES)C. Once emerged, corn grew at a faster rate than the two weed species;The effects of different planting dates, tillage practices, and soil temperatures on seedling emergence and growth rates were evaluated in field studies. Corn was planted at approximately two-week intervals from late April to early June. For each of the four planting dates, three different tillage treatments were evaluated: no tillage, 5-7 cm tillage, and 10-12 cm tillage. Corn emergence was favored by the later planting dates. Giant foxtail and velvetleaf emergence were greatest with the first and second planting dates, respectively. Depth of tillage did not affect corn seedling emergence. Giant foxtail and velvetleaf emergence were less in no tillage areas as the season progressed. Corn dry matter accumulation was greater with the last planting date and with the deeper 10-12 cm tillage depth. Velvetleaf growth was most rapid with the third planting date and the 10-12 cm tillage;Heating cables were used to increase soil temperatures in no tillage and 10-12 cm tilled areas. Early seedling counts revealed an increase in the number of emerged corn and giant foxtail plants with increased soil temperatures. Dry matter accumulation data suggested that the growth of all three species was positively affected by increased soil temperature. Corn growth was greater with tillage of 10-12 cm than in no tillage areas, whereas giant foxtail and velvetleaf growth was not affected by the different tillage treatments.



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Kristine Peterson Schaefer



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99 pages