Bibliography : leaves 159-184. This study found at least three mechanisms of resistance to the acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides. A modified target -site was responsible for moderate and high resistance to herbicides at the whole plant level. Enhanced herbicide metabolism and reduced translocation of herbicide to the target site was observed in one resistant biotype each.

Bibliography: leaves 128-146. Study was undertaken to determine the occurence and species incidence of wild oats in a major cropping region of southern Australia. Population dynamic studies were undertaken at two sites to define the seed bank decline and emergence pattern of several wild oat populations over a three year period. Management studies were conducted to determine appropriate strategies for the control of wild oats in southern Australian farming systems.

Bibliography : leaves 159-184. / xv, 191 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / This study found at least three mechanisms of resistance to the acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides. A modified target -site was responsible for moderate and high resistance to herbicides at the whole plant level. Enhanced herbicide metabolism and reduced translocation of herbicide to the target site was observed in one resistant biotype each. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1996

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliography.

The germination and emergence of a seedling, or seedling recruitment remains an essential process in the establishment of a plant. This establishment can be limited by the availability of microsites within the soil profile, or the availability of seed within a given area. Three field experiments were initiated in Saskatchewan, Canada to examine the relative effect of seed and microsite limitations on weed seedling recruitment. The first experiment examined the effect of landscape position as well as nitrogen (N) rate and tillage system (zero tillage vs. conventional tillage) on weed seedling recruitment from an indigenous weed population. Survey results indicated habitat differentiation of the weed population with wild oat and cleavers preferentially recruiting in the lower landscape positions, Russian thistle and Kochia in the upper landscape positions, while green foxtail recruited in high levels on all landscape positions. This suggested that different weed species have different microsite requirements for weed seedling recruitment across contrasting landscape positions. The second field experiment examined the effect of landscape position and moisture availability on weed seedling recruitment from an artificial hand-seeded weed seedbank. This experiment indicated that seed limitation remained a very important factor, but even when irrigated, total seedling recruitment did not reach maximum recruitment, indicating water was not the only limiting resource for weed seedling recruitment. Microsite limitations were greatest on the upper slope position for all species with green foxtail having the greatest overall recruitment of the species across all landscapes and moisture regimes. The third experiment examined the effect of tillage system and density on weed seedling recruitment of wild oat, green foxtail, and wild mustard. Again, weed seedling recruitment remained a function of both microsite and seed limitations as absolute recruitment values increased for each density examined in this experiment. The agronomic significance of microsite limitation was negligible as high weed population numbers occurred for the highest weed seeding densities. Overall, microsite limitations remained negligible in these experiments for arable agriculture with the main influence on weed seedling recruitment most often being seed limitation in the natural seedbank.

Abstract Ecological based weed management strategies are imperative in cropping systems when herbicide use is limited or prohibited. Herbicides are not applicable in controlling wild oat (Avena fatua L.) in oat (Avena sativa L.) cropping systems, as they are closely related. Moreover, herbicide use is prohibited in organic oat cultivation, resulting in a need for developing alternative weed management strategies. Enhancing the crop competitive ability (CA) can be an essential strategy in managing weeds in such instances. Two studies were carried with the objectives to: 1) evaluate newly developed oat genotypes for their CA against wild oat; and 2) develop a competitive organic oat cropping system integrating mechanical and cultural weed control practices. In the first study, seven oat lines deliberately bred for enhanced CA and their two parental cultivars were evaluated for the CA with wild oat. The genotypes yielded similarly in the presence and in the absence of wild oat competition. The tall oat line SA050479 with greater seedling leaf size was more wild oat suppressive among all lines. Moreover, SA050479 had greater yield potential and grain quality; thus, it has the potential to be developed as a commercial wild oat suppressive cultivar. The second study used two contrasting levels of genotype, row spacing, crop density and a post-emergence harrowing and a non-harrowed control in two organic oat fields to develop an integrated weed management system. High crop density and harrowing increased the grain yield by 11% and 13% respectively. The competitive cultivar CDC Baler and high crop density (500 plants m-2) reduced weed biomass by 22% and 52% respectively. Harrowing reduced weed density by more than 50% in three site-years. The cultural and mechanical weed control practices when combined were additive in increasing grain yield and reducing weed biomass. Oat seed yields were increased by 25% when high crop density planting and harrowing were combined. Similarly, the combined effect of competitive cultivar, high crop density, and post-emergence harrowing were greater as weed biomass was reduced by 71%. The outcome of this project implies the importance of enhancing the crop CA by means of crop breeding and integrating cultural and mechanical weed control strategies. Furthermore, this study was able to identify the importance of ecological based weed management strategies in order to overcome the constraints in weed management in present oat cropping systems.

The inability to control wild oat (Avena fatua L.) in oat (Avena sativa L.) crops by chemical means limits growers to the use of cultural control methods. Delayed seeding is the most commonly used measure; however, both crop yield and quality may suffer as a result. The objectives of this research were to i) determine if western Canadian oat genotypes differ in competitive ability, ii) determine the effect of increased plant populations on oat wild oat competition, iii) determine the effect of wild oat competition on oat quality, and iv) establish whether or not oat genotype and seed size affect germination characteristics under low temperature and moisture stress. These objectives were tested using field and laboratory experiments. Morphologically diverse oat genotypes differed in their ability to both tolerate wild oat competition and interfere with wild oat growth. Although low yielding under weed-free conditions, when subject to wild oat competition CDC Bell was able to maintain yield, reduce wild oat seed production and was the most competitive of the genotypes examined. Increased plant populations achieved through higher seeding rates provide an effective means by which to enhance the competitive ability of oat genotypes resulting in reduced yield loss and wild oat seed production. With the exception of the percentage of wild oat seed in harvested oat samples, wild oat competition had minimal effect on oat quality. Differences in germination characteristics were observed among the genotypes examined. Conclusions that emerge from this research are that i) oat genotypes differ in their ability to tolerate and interfere with wild oat competition, ii) increased plant populations may provide a long-term control measure that may reduce weed seed contribution to the soil seedbank as well as enhance the competitive ability of oat, iii) wild oat competition has minimal effect on milling oat quality with the exception of percentage of wild oat seed in harvested samples and iv) that median germination time varies among oat genotypes.

The inability to control wild oat (Avena fatua L.) in oat (Avena sativa L.) crops by chemical means limits growers to the use of cultural control methods. Delayed seeding is the most commonly used measure; however, both crop yield and quality may suffer as a result. The objectives of this research were to i) determine if western Canadian oat genotypes differ in competitive ability, ii) determine the effect of increased plant populations on oat wild oat competition, iii) determine the effect of wild oat competition on oat quality, and iv) establish whether or not oat genotype and seed size affect germination characteristics under low temperature and moisture stress. These objectives were tested using field and laboratory experiments. Morphologically diverse oat genotypes differed in their ability to both tolerate wild oat competition and interfere with wild oat growth. Although low yielding under weed-free conditions, when subject to wild oat competition CDC Bell was able to maintain yield, reduce wild oat seed production and was the most competitive of the genotypes examined. Increased plant populations achieved through higher seeding rates provide an effective means by which to enhance the competitive ability of oat genotypes resulting in reduced yield loss and wild oat seed production. With the exception of the percentage of wild oat seed in harvested oat samples, wild oat competition had minimal effect on oat quality. Differences in germination characteristics were observed among the genotypes examined. Conclusions that emerge from this research are that i) oat genotypes differ in their ability to tolerate and interfere with wild oat competition, ii) increased plant populations may provide a long-term control measure that may reduce weed seed contribution to the soil seedbank as well as enhance the competitive ability of oat, iii) wild oat competition has minimal effect on milling oat quality with the exception of percentage of wild oat seed in harvested samples and iv) that median germination time varies among oat genotypes.

The goal of the project was to enhance the period of weed growth prior to seeding in order to reduce weed emergence and weed competition after the crop has been planted. Weed growth was stimulated using either light tillage or by applying nitrogen fertilizer early in the spring. Light disturbance significantly increased pre-seed weed emergence while early applied nitrogen did not appear to have an effect. Post seeding weed emergence levels and weed biomass were similar among the light tillage and early nitrogen treatments. Therefore the goal of decreasing weed competition after seeding was not attained. Future research should focus on long-term strategies to reduce weed populations in field rather than seasonal strategies. / October 2006

The germination and emergence of a seedling, or seedling recruitment remains an essential process in the establishment of a plant. This establishment can be limited by the availability of microsites within the soil profile, or the availability of seed within a given area. Three field experiments were initiated in Saskatchewan, Canada to examine the relative effect of seed and microsite limitations on weed seedling recruitment. The first experiment examined the effect of landscape position as well as nitrogen (N) rate and tillage system (zero tillage vs. conventional tillage) on weed seedling recruitment from an indigenous weed population. Survey results indicated habitat differentiation of the weed population with wild oat and cleavers preferentially recruiting in the lower landscape positions, Russian thistle and Kochia in the upper landscape positions, while green foxtail recruited in high levels on all landscape positions. This suggested that different weed species have different microsite requirements for weed seedling recruitment across contrasting landscape positions. The second field experiment examined the effect of landscape position and moisture availability on weed seedling recruitment from an artificial hand-seeded weed seedbank. This experiment indicated that seed limitation remained a very important factor, but even when irrigated, total seedling recruitment did not reach maximum recruitment, indicating water was not the only limiting resource for weed seedling recruitment. Microsite limitations were greatest on the upper slope position for all species with green foxtail having the greatest overall recruitment of the species across all landscapes and moisture regimes. The third experiment examined the effect of tillage system and density on weed seedling recruitment of wild oat, green foxtail, and wild mustard. Again, weed seedling recruitment remained a function of both microsite and seed limitations as absolute recruitment values increased for each density examined in this experiment. The agronomic significance of microsite limitation was negligible as high weed population numbers occurred for the highest weed seeding densities. Overall, microsite limitations remained negligible in these experiments for arable agriculture with the main influence on weed seedling recruitment most often being seed limitation in the natural seedbank.