Theses and Dissertations at Montana State University (MSU)
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Item Effect of agronomic practices on disease incidence, severity, and impacts in Montana cropping systems(Montana State University - Bozeman, College of Agriculture, 2017) Ranabhat, Nar Bahadur; Chairperson, Graduate Committee: Fabian D. Menalled; Mary Burrows (co-chair)Integrated pest management is at the foundation of sustainable cropping systems. This thesis investigated 1) the influence of alternative host plants and agronomic practices on Wheat streak mosaic virus (WSMV) risk, and 2) how cover crop termination methods influence diseases in grazed organic, tilled organic, and chemical no-till systems. To assess the influence of alternative hosts including volunteer wheat, Bromus tectorum, Setaria viridis, and Zea mays on WSMV incidence and its vector, the wheat curl mite (Aceria tosichella, WCM) movement during the fall, a 'trap plant' capture system was used. In 2013, alternative hosts had similar WCM infestation levels compared to the control in most weeks. In 2014, spring planted B. tectorum and volunteer wheat increased the incidence of WSMV and abundance of WCM compared to control. In a study assessing the impact of planting date and winter wheat variety on WSMV incidence, there was almost no infection of WSMV across resistant wheat varieties. However, Pronghorn, a susceptible wheat variety, had a higher WSMV incidence at the early planting date than recommended and late planting dates. In a companion study of the impact of wheat variety and timing of N application on WSMV incidence, results did not differ across N application timing across resistant varieties. However, early spring N application in 2014 had a higher WSMV incidence compared to fall and late spring N application in Pronghorn and Yellowstone. A study assessing the impact of cropping systems on diseases indicated that disease incidence during the transition to organic period in 2013 and 2014 as well as an established organic year, 2016, was similar at tillering and flowering stages of winter wheat between the grazed organic, tilled organic, and chemical no till system. However, disease incidence was variable between systems at the matured growth stage in 2014 and 2016. In 2015, disease incidence varied between systems at all growth stages. Overall, disease severity was similar in winter wheat between grazed organic, tilled organic, and chemical no till systems, indicating disease is not a major constraint to organic methods of crop production during the transition period.Item Factors involved in the success and establishment of the field bindweed gall mite Aceria malherbae Nuzzaci (Acari: eriophyidae)(Montana State University - Bozeman, College of Agriculture, 2014) Konigsberg, Evelyn Rivka; Co-chairs, Graduate Committee: Jeffrey Littlefield and Tracy M. SterlingDespite years of study and management, field bindweed (Convolvulus arvensis L., Fam.: Convolvulaceae) remains a problematic invasive species across the United States and is in need of better management options. Studies were conducted to determine factors affecting the establishment and performance of the biological control agent Aceria malherbae Nuzzaci. To determine the effects of sub-lethal herbicide applications on gall induction and development of A. malherbae, a bioassay was conducted with four herbicides, each having different modes of action. Atrazine, glyphosate, imazapic, and picloram were applied at 25% of their recommended dosages on plants infested and not infested with A. malherbae. Sub-lethal herbicide applications had an adverse effect on plant stem height, total stem length, numbers of leaves or branches, or on above-ground or below-ground biomass; whereas A. malherbae did not. Synergistic impacts of herbicide applications and A. malherbae on growth parameters of field bindweed were not observed. Pre- and post-spray gall counts were not significantly different, indicating that gall induction and development was not altered by these sub-lethal dosages. The establishment and effectiveness of A. malherbae has been reported to vary across western North America, with genetic variation of field bindweed as a possible contributing factor. Four field bindweed populations, collected from Montana, California, Oregon, and New Mexico, were exposed to A. malherbae to determine if growth parameters conducive or detrimental to the development of the mite vary among plant populations. When grown in a common environment, plant height, stem length, and number of branches and leaves significantly varied among populations although biomass did not differ. Galling by A. malherbae did not impact field bindweed growth, except for slight reduction in root biomass of infested plants. Gall induction was lower on plants from New Mexico than Oregon. Field studies assessed the relationship between habitat characteristics and plant cover and the presence and abundance of the mite. Multidimensional scaling of site characteristics indicated a spatial relationship, though no habitat relationship, among established A. malherbae populations. In within-field studies, a significant positive relationship was observed between percent grass cover and mite abundance and a negative relationship between field bindweed and mite abundance.