Yellow starthistle (Centaurea solstitialis L.) is an introduced Asteraceae that has become established on 10 million acres in the Pacific Northwest and California. This weed functions as an annual or short-lived perennial and depends on seeds for reproduction. Strategies of control that reduce plant fitness or lower seed production or viability may help limit the rate of spread of yellow starthistle. Previous work has shown that grazing and mowing can influence seed production. This study tested the hypothesis that proper timing and frequency of defoliation can reduce the number and viability of seeds produced. The study was conducted in Umatilla County, Oregon using a randomized block design with 4 replications of each of 4 defoliation treatments: (1) single defoliation at the bolting stage; (2) single defoliation at the bud stage; (3) two defoliations, once at the bolting stage and again at the bud stage; (4) non-defoliated control. Each of 4 blocks consisted of a 12 x 12 m area, with 16 plots measuring 3 x 3 m. Plants were defoliated at ground level using a gas-powered string-type mower. Response measurements were collected at the end of the growing season (September) following potential regrowth and included: (1) number of seedheads per plant; (2) number of seeds per seedhead; (3) number of seeds per plant; (4) number of seeds m⁻², (5) seed viability (% germination rates). Supporting measurements included: seedhead diameter; plant height, number of branches per plant; pre-dawn xylem pressure; soil moisture; and documentation of 5 biological control insect species. A single defoliation at bolting resulted in fewer seeds per seedhead, and fewer seeds per plant than non-defoliated controls. A single defoliation at the floral bud stage or repeated defoliation (bolting and again at the bud stage) resulted in equally fewer seeds per plant and fewer seeds m⁻² compared to non-defoliated controls. There was no statistical difference in percent germination of seeds among treatments. Defoliation had no effect on the infestation rates of seedheads by biological control insects. A second study examined nutrient content of yellow starthistle during 6 phenological stages from sites in Union, Baker and Umatilla Counties, Oregon during each of 2 years. Acid detergent fiber, lignin, cellulose and neutral detergent fiber contents increased through phenological development. Crude protein ranged from 16.7 to 5.0%. In Vitro dry matter digestibility ranged from 84.8% to 57.0%. Mineral nutrients P, K, CA, Mg, Mn, Fe, Cu, Zn, and Na were analyzed and determined to be adequate for maintenance needs of ewes. / Graduation date: 2002

Thesis (M.S.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains vii, 109 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 44-50).

Cotton, Gossypium hirsutum L., leaf grade values can significantly increase with remnants of leaf and bract materials, and can result in increased ginning costs and discounts to the producer. Cotton classed through the USDA-AMS Classing Office in Corpus Christi, Texas has reported increases in leaf grade values beginning in 2000 (USDA, 2012). The impacts of the interaction of agronomic characteristics of cotton cultivars with those of various harvest aid regimes were studied over three growing seasons, and data were used to narrow possible contributors to the observed increased leaf grade values. Multiple trials were conducted throughout the Coastal Bend and Blackland Prairie of Texas, in addition to Tifton, Georgia. Cotton was harvested, lint samples were ginned in a microgin, and lint quality was quantified with HVI. Harvest aid regimes selected provided a broad range of defoliation and desiccation, from a multiple herbicidal and hormonal modes-of-action. Defoliation levels ranged from 0 to 96% and desiccation levels ranged from 0 to 90%. Harvest aid treatments had no impact (P≤0.05) on leaf grade values for either of the years of the trials. Multiple trials were conducted in five counties in Texas, including the Lower and Upper Coastal Bend and the Blackland Prairie, and were defoliated with a uniform harvest aid treatment to identify leaf and bract morphological differences, and to determine their role in leaf grade. Multi-acre module trials were conducted with a smooth leaf cultivar and a hairy leaf cultivar to obtain leaf grade values following commercial ginning. Leaf and bract pubescence, and leaf and bract area were collected to analyze the resulting impact on cotton leaf grade values. Visual quantification of leaf and bract trichome density was quantified on 10 youngest fully-expanded leaves and 10 mid-canopy full sized bolls, respectively, when cotton was at physiological cut-out. Trichome density quantification indicated substantial variation in cultivars and discrepancies from company based rating systems. Leaf grades values generally increased with increasing trichomes densities, although not always statistically significant. In the split plot cultivar and harvest aid trial, harvest aid efficacy was similar for each of the cultivars, but cultivar trichome density was positively influence the cotton leaf grade value.

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Bibliography: leaves 209-254. / xv, 254 leaves : ill. (chiefly col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Experiments detailed in this thesis, evaluate the impact of various herbicides and herbicide mixtures on the growth, nodulation and nitrogen fixation of annual pasture legumes, the efficacy of the herbicides for weed control, and the potential role of mechanical defoliation to replace herbicides, leading to lower cost and more sustainable farming systems. / Thesis (Ph.D.)--University of Adelaide, Dept. of Plant Science, 1996

Thesis (Ph. D.)--University of Adelaide, Dept. of Plant Physiology, 1985. / Includes bibliographical references (leaves 245-271).

Thesis (Ph. D.)--University of Canterbury, 2007. / Typescript (photocopy). "September 2007." Includes bibliographical references (p. 147-179). Also available via the World Wide Web.

Thesis (M.S.)--West Virginia University, 2000. / Title from document title page. Document formatted into pages; contains vii, 59 p. : ill. (some col.), maps. Vita. Includes abstract. Includes bibliographical references (p. 23-28).

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliographical references.

Orientador: Jairo Osvaldo Cazetta / Banca: Marcelo Murad Magalhães / Banca: Paulo Cesar Magalhães / Banca: Domingos Fornasieri Filho / Banca: Durvalina Maria Mathias dos Santos / Resumo: Com o objetivo de avaliar diferentes estresses sobre o acúmulo e partição de massa seca, abortamento, desenvolvimento, produção de grãos e concentração de metabólitos glicídicos e nitrogenados em plantas de milho, conduziuse um experimento em casa de vegetação. Os tratamentos foram: testemunha; plantas com desfolhamento de 66%; omissão do nitrogênio; déficit hídrico (20 - 30% da capacidade de retenção); sombreamento de 70%. Os estresses foram impostos dos dois aos quarenta dias após a polinização (DAP) e as avaliações realizadas em cinco coletas aos 0, 10, 20, 30 e 40 DAP. A omissão de N na fase reprodutiva não afetou a massa seca das plantas e não promoveu alterações nos grãos das plantas de milho, em função da grande remobilização deste elemento acumulado nas folhas e colmos durante o período vegetativo. O desfolhamento reduziu o acúmulo de massa seca no colmo e na espiga, causou abortamento de grãos, não afetou a massa dos grãos remanescentes, resultando em menor número e produção de grãos por planta. O sombreamento intensificou a translocação de fotossintatos do colmo e folhas para os grãos, causou redução no acúmulo de massa seca na planta, abortamento de grãos, menor peso dos grãos remanescentes, menor acúmulo de amido e menor produção de grãos por planta. O déficit hídrico reduziu a área foliar, a fotossíntese, o período de enchimento dos grãos, o acúmulo de MS na planta e a translocação de fotoassimilados para os grãos, resultando em abortamento de grãos do ápice da espiga, acúmulo de açúcares redutores e aminoácidos livres nas folhas e colmos e menor massa de grãos e produção por planta. A redução na produção foi maior no estresse por déficit hídrico, sombreamento de 70%, desfolhamento de 66% e deficiência de N, sendo o número de grãos por espiga e peso médio dos grãos os componentes da produção mais afetados. / Abstract: To evaluate the effect of different stress on the accumulation and distribution of dry matter, abortion, development and production of grains and concentration of glycidic and nitrogen metabolites in maize plant, it was conducted an experiment on greenhouse conditions. The following treatments were used: control; defoliation (plants 66% defoliated); nitrogen omission; water deficit (20 - 30% of the retention capacity); shading (70%). The stress factors were imposed from two to forty days after pollination (DAP) and the analyses at 0, 10, 20, 30 and 40 DAP. The nitrogen omission at the reproductive stage did not affect plant dry mass or grains because of the high rate of remobilization of the N accumulated in leaves and stems during the vegetative stage. Defoliation reduced the dry matter accumulation in the stem and ears, increased kernel abortion, no caused any effect on photoassimilate translocation or weight from remaining grains. Also, resulted in a decrease on the total-N level, amino acids, grain reducing sugars and starch, fewer grains and lower production per plant. Shading intensified photoassimilate translocation indicating that in shaded plants the photosynthesis limitation is supplied by the high remobilization rate of reducing sugars, sucrose and starch from the stem and leaves to the grain. However, this stress causes reduction of dry matter accumulation, kernel abortion, and lower weight of remaining grains, starch accumulation and production of grains per plant. The water deficit reduced leaf area, photosynthesis, grain filling period, dry matter accumulation and photoassimilate translocation from vegetative organs to kernels, resulting in kernel abortion at the ear top, accumulation of reducing sugars and free amino acids in leaves and stems and lower weight of 1,000 grains and production per plant... (Complete abstract, click electronic address below) / Doutor