Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references (leaves 56-61). Also available on the World Wide Web.

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Research was conducted in 2013 and 2014 to evaluate the influence of cotton (Gossypium hirsutum L.) insecticidal seed treatments, planting date, and preemergence herbicides on thrips (Frankliniella fusca) infestations in cotton. Studies included a preemergence and soil texture evaluation on cotton development, an evaluation of thrips infestations, cotton development and yield following application of various preemergence herbicides and insecticidal seed treatments, and a planting date evaluation where different cultivars where planted with exclusion or inclusion of preemergence herbicide use at four different planting dates to determine the effect on thrips infestations, cotton development, and yield.

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Weed resistance has decreased the number of herbicides that provide effective weed control in cotton. Studies were conducted to determine weed control efficacy and crop safety in cotton with herbicides not currently labeled for use in the crop. Herbicides were applied at two different timings near Starkville and Brooksville, MS. Cotton injury following application of ametryn, bentazon, florpyrauxifen-benzyl, topramezone and tolpyralate at the 3-5 or the 8-10 node growth stage ranged from 24 to 43% and 15 to 51%, respectively, up to 56 days after application. Except for bentazon, applying non-labeled herbicides to cotton at the 3-5 or 8-10 node growth stage decreased seedcotton yield 25 to 44%. Application of bentazon had no effect on yield when applied to cotton at both growth stages and may need to be further evaluated for use in cotton.

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Bermudagrass (Cynodon dactylon (L). Pers.) is considered to be one of the most difficult to control grass weeds in turf throughout the U.S. Recent breeding efforts have produced much more desirable bermudagrass cultivars, and therefore its use has increased. Ironically, as bermudagrass use becomes more popular it poses even greater difficulties to the turf manager. The need to control these warm season turfgrass species, without causing injury to other desirable turfgrass species, is one of the most intractable problems a turf specialist encounters. Herbicides previously used to selectively control bermudagrass such as siduron and oxadiazon have proven to be of only minimal efficacy or to induce significant injury to other desirable turfgrasses. Tests conducted in 1993, 1994 and 1995 have indicated that fenoxaprop plus fluazifop (Horizon 2000R) controlled bermudagrass effectively. Six bermudagrass (Cynodon dactylon) cultivars and tall fescue (Festuca arundinacea) were used in the susceptibility studies. Visual control and cover ratings were taken at two-week intervals until ten weeks after the final treatment. Sequential applications of labeled rates of fenoxaprop or fluazifop alone only temporarily controlled bermudagrass shoots. Horizon 2000 applied at 0.40 kg ai/ha in three sequential applications proved effective in controlling bermudagrass rhizomes and stolons. From results of previous studies and research conducted here it has been hypothesized that synergistic effects of fenoxaprop on fluazifop allow both differential control of various bermudagrass cultivars and increased tall fescue tolerance to these herbicides. / Master of Science

Thesis (Ph. D.)--Oregon State University, 2007. / Printout. Includes bibliographical references. Also available on the World Wide Web.

Auxinic herbicide-resistant (i.e., resistant to 2,4-D and MCPA) wild radish (Raphanus raphanistrum L.) was discovered in the Western Australian wheatbelt, providing an opportunity to integrate auxinic herbicide resistance into cultivated radish (R. sativus L.) using conventional breeding methods. It was hypothesized that the inheritance of auxinic herbicide resistance in wild radish is conferred by a single, dominant nuclear gene and, therefore, will be relatively easy to introgress from wild radish to cultivated radish; and the mechanism of auxinic herbicide resistance in wild radish is through an altered target-site. Visual injury data of the F2 progeny suggested that resistance was conferred by a quantitative trait with the susceptible allele(s) exhibiting dominance with minor cytoplasmically inherited genes masking the susceptible trait. In conclusion, the resistance allele(s) were quantitative and, thus, make selection for resistance difficult. Therefore, the introgression of the resistance allele(s) was not successfully completed. To determine the mechanism of resistance, the wild radish plants resistant WARR6-26 (R) and susceptible WARR7-5 (S) were treated with radiolabeled MCPA. There was no difference in metabolism of [14C]MCPA between R and S plants. Based upon the decline in the total 14C recovered over 72 h in R and S it was clear that both were “losing” [14C]MCPA; however, R plants were losing MCPA more rapidly. It was hypothesized that because R plants exude 14C more rapidly from their roots than S plants, this accounted for the resistance of R plants.