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Item Aphanomyces euteiches spatial distribution, host studies, and characterization in Montana(Montana State University - Bozeman, College of Agriculture, 2022) Murphy, Carmen Yvette; Chairperson, Graduate Committee: Mary BurrowsGrowing pulse crops in Montana has been inhibited by biotic constraints to production, including a complex of pathogens causing root rot. Aphanomyces root rot, caused by the soilborne oomycete, Aphanomyces euteiches, causes plant stunting and yellowing, root browning and constriction, and reduces yield in dry pea and lentil in the state. Twelve fields with a history of pulse root rot were sampled in northeast Montana with three 100 m entrance transects and one 50 m transect at a low spot or problem area. Soil from each 10 m quadrat within transects was assessed for root rot using a greenhouse bioassay with a susceptible dry pea variety, and with PCR. Samples were also analyzed for soil properties and nutrients. Distribution of the pathogen was sporadic in most fields, except for fields that had been growing pulses in a consistent rotation, where root rot severity was high and consistent. Soil pH, organic matter, potassium, and sulfur concentration were correlated with Aphanomyces root rot, and isolates varied in their response to acidic pH in vitro. Using a highly virulent A. euteiches isolate, greenhouse trials were conducted to assess the pathogen load of inoculated soil after growing host and non-host plant species, measured with a bioassay. Greenhouse pots were inoculated with 500 oospores per gram prior to planting plant treatments. Growing host plants resulted in higher root rot severity on dry pea bait plants compared to non-host plant treatments. When five cycles of plants were grown in greenhouse pots inoculated with A. euteiches, using five 'rotation' treatments, one treatment with three consecutive rounds of non-host plants reduced the disease severity score in one trial repetition compared to treatments with less than three successive rounds growing a non-host. This research indicates that sampling strategies for Aphanomyces root rot requires multiple sampling locations within a field to enhance the probability of detection, and that crop rotation is an important tool for management of pathogen load in the soil.Item Management of Kochia (Bassia scoparia) in a time of herbicide resistance(Montana State University - Bozeman, College of Agriculture, 2020) Lim, Charlemagne Ajoc; Chairperson, Graduate Committee: Alan T. Dyer; Alan Dyer and Prashant Jha were co-authors of the article, 'Kochia (Bassia scoparia) growth and fecundity under different crops and weed densities' submitted to the journal 'Weed science journal' which is contained within this dissertation.; Alan Dyer and Prashant Jha were co-authors of the article, 'Survival and reproductive fitness of glyphosate-resistant kochia (Bassia scoparia) in the presence of glyphosate' submitted to the journal 'Weed technology journal' which is contained within this dissertation.; Alan Dyer and Prashant Jha were co-authors of the article, 'Survival, growth and fecundity of Dicamba-resistant kochia (Bassia scoparia) in the absence and presence of Dicamba' submitted to the journal 'Weed technology journal' which is contained within this dissertation.Kochia [Bassia scoparia (L.) A. J. Scott] is one of the most troublesome weeds in the US Great Plains. This is exacerbated by the development of herbicide-resistant kochia populations which necessitates more ecologically driven approaches for its control. This research examined the competitive effects of four crops (sugar beet, soybean, barley and corn) in combination with kochia densities (3, 13, 24, 47, 94 and 188 plants m-2) on kochia development and kochia seed production. Corn had greatest effect in reducing kochia biomass and seed production. Barley had greatest effect in delaying kochia flowering which happened after barley senesced at 113 days after kochia emergence. Soybean and sugar beet had the least effect in reducing kochia biomass and seed production, respectively, relative to fallow. This research also reports the fitness of glyphosate-resistant kochia and dicamba-resistant kochia in the presence and absence of glyphosate and dicamba selection, respectively, under field conditions. Glyphosate-resistant kochia showed limited fitness cost (less seed weight and seed radicle length relative to the susceptible) in the absence of glyphosate selection and reduced reproductive fitness (seed production) in the presence of increasing glyphosate selection. In the absence of dicamba selection, dicamba-resistant kochia showed a fitness cost (reduced growth and seed production relative to the susceptible) associated with dicamba resistance with greater fitness cost observed with increased level of resistance. Dicamba-resistant kochia also showed reduced reproductive fitness (seed production) in the presence of increasing dicamba selection. Overall, this research provides information on the growth and reproductive fitness of glyphosate-resistant kochia and dicamba-resistant kochia in the presence and absence of glyphosate and dicamba selection, respectively. Furthermore, this research provides insights on the competitive abilities of different but financially viable rotational crops for kochia management in Montana.Item Elucidating the effect of anthropogenic land management on soil nematode community structure(Montana State University - Bozeman, College of Agriculture, 2019) Burkhardt, Andy; Chairperson, Graduate Committee: Jamie Sherman; Shabeg S. Briar, John M. Martin, Patrick M. Carr, Jennifer Lachowiec, Cathy Zabinski, David W. Roberts, Perry Miller and Jamie Sherman were co-authors of the article, 'Perennial crop legacy effects on nematode community structure in semi-arid wheat systems' in the journal 'Applied soil ecology' which is contained within this thesis.; Shabeg S. Briar, John M. Martin, Patrick M. Carr and Jamie Sherman were co-authors of the article, 'Characterization of soil nematode community structure in semi-arid dryland barley (Hordeum vulgare L.) systems' which is contained within this thesis.Nematodes as a taxonomic phylum are incredibly diverse and play an important role in soil biology, nutrient cycling, and soil food web function. Nematodes can be categorized into five major trophic groups including bacterivores, fungivores, herbivores, predators, and omnivores. Plant-parasitic nematodes (PPNs) affect soil food web resources through direct herbivory, while free-living (non-pathogenic) bacterivores and fungivores graze on microbes and contribute significantly to soil nutrient pools. Predatory nematodes regulate the soil food web by preying on other nematodes and invertebrates in the soil. An unbalanced soil food web community can lead to unintended impacts to other species and create a cascading effect. In agriculture, this impact can lead to low crop production and reduced revenue by means of soil ecological degradation. The goal of this project was to elucidate the nematode community structure changes under different management strategies in both agricultural and range settings. The hypotheses we tested were 1) that crop rotations eliminating fallow would positively and significantly impact the soil nematode community that would in turn self-regulate the PPN population and 2) native sagebrush steppe would have a more diverse nematode community than converted sagebrush steppe managed for livestock grazing or other uses. We did so with the following studies: 1. Quantitatively assessed nematode community structure under barley monoculture and barley-fallow vs. barley-pea rotations using multiple ecological measures and indices and correlated those measures and indices with soil chemical and physical properties as well as agronomic parameters of each system. 2. Quantitatively assessed nematode community structure under wheat-tilled fallow, wheat-no-till fallow, and no-till wheat monoculture vs. several no-till wheat-pulse rotations using multiple ecological measures and indices to evaluate long term impacts of cropping system to the nematode community. 3. Quantified taxonomic diversity and ecological indices of disturbed and undisturbed sagebrush steppe in the Bangtail Mountains west of Wilsall, Montana to evaluate disturbance regimes in a reclaimed environment.Item Pea in Rotation with Wheat Reduced Uncertainty of Economic Returns in Southwest Montana(2015-01) Miller, Perry R.; Bekkerman, Anton; Jones, Clain A.; Burgess, Macdonald H.; Holmes, Jeffrey A.; Engel, Richard E.Pea (Pisum sativum L.) is increasingly being rotated with wheat (Triticum aestivum L.) in Montana. Our objective was to compare economic net returns among wheat-only and pea–wheat systems during an established 4-yr crop rotation. The experimental design included three wheat-only (tilled fallow–wheat, no-till fallow–wheat, no-till continuous wheat) and three no-till pea–wheat (pea–wheat, pea brown manure–wheat, and pea forage–wheat) systems as main plots, and high and low available N rates as subplots. Net returns were calculated as the difference between market revenues and operation and input costs associated with machinery, seed and seed treatment, fertilizer, and pesticides. Gross returns for wheat were adjusted to reflect grain protein at “flat” and “sharp” discount/premium schedules based on historical Montana elevator schedules. Cumulative net returns were calculated for four scenarios including high and low available N rates and flat and sharp protein discount/premium schedules. Pea–wheat consistently had the greatest net returns among the six systems studied. Pea fallow–wheat systems exhibited greater economic stability across scenarios but had greater 4-yr returns (US$287 ha–1) than fallow–wheat systems only under the low N rate and sharp protein discount schedule scenario. We concluded that pea–wheat systems can reduce net return uncertainties relative to wheat-only systems under contrasting N fertility regimes, and variable wheat protein discount schedules in southwestern Montana. This implies that pea–wheat rotations, which protected wheat yield and/or protein levels under varying N fertility management, can reduce farmers’ exposure to annual economic variability.Item Evaluation of alternative crops for management of Pratylenchus neglectus in Montana winter wheat production(Montana State University - Bozeman, College of Agriculture, 2010) Zuck, Peter Christopher; Chairperson, Graduate Committee: Alan T. Dyer.A series of crop rotations were evaluated for their impacts on soil-borne populations of root lesion nematodes, Pratylenchus neglectus. Population changes, measured as the ratio of P. neglectus adults counted at harvest to those counted at planting time, was recorded under a series of two-year rotations alternating winter wheat with either fallow, barley, pea, lentil, canola, and camelina. Fallow, barley, pea, and camelina were found to have a neutral effect on nematode populations (p < 0.001). Winter wheat and canola caused significant increases in populations, while lentils caused significant decreases (p < 0.001). Populations were sustained through winter following winter wheat and barley, but not canola, camelina, pea, lentil, or fallow treatments (p < 0.001). In addition to the rotation study, cultivars of barley and canola were evaluated for their resistance to P. neglectus. Greenhouse trials for barley showed significant differences among 19 cultivars tested (p < 0.001), with a 5-fold difference in P. neglectus multiplication separating the least- from the most resistant. Separation among cultivars was not found with canola (p = 0.20). The information gathered in this study will help Montana wheat growers better understand the impacts of their crop selections on this important pest.