Theses and Dissertations at Montana State University (MSU)

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Pest management challenges and climate change in water limited winter wheat agroecosystems in southwestern Montana
(Montana State University - Bozeman, College of Agriculture, 2020) Nixon, Madison Grace; Chairperson, Graduate Committee: Fabian D. Menalled
Dryland winter wheat production is influenced by many environmental factors including climate, disease, and resource availability. In Montana, Bromus tectorum (cheatgrass) and Fusarium pseudograminearum (a fungus causing root crown rot) are major winter wheat pests; reducing yield and grain quality. However, little is known how climate change and resource availability impact winter wheat, B. tectorum, and F. pseudograminearum individually as well as their multi-trophic interactions. Thus, this research aimed to 1) Determine the susceptibility of B. tectorum to F. pseudograminearum and assess how CO 2 and nitrogen impact their growth, and 2) Evaluate how elevated temperature, reduced precipitation, and plant competition impact winter wheat and B. tectorum growth and reproduction. Utilizing growth chambers, high and low nitrogen treatments, fungal inoculated and uninoculated treatments, and ambient and elevated CO 2 treatments, Bromus tectorum was found to be a host of F. pseudograminearum, and the fungus significantly reduced root, shoot and total biomass, as well as primary physiological processes of B. tectorum. Fusarium pseudograminearum infection was not impacted by nitrogen or CO 2 level. Low nitrogen increased emergence and root production early on, while high nitrogen increased shoot production at later growth stages. Low nitrogen also improved stomatal conductance and transpiration rate. High CO 2 increased B. tectorum root, shoot, and biomass production, as well as intercellular CO 2. An interaction between ambient CO 2 and low nitrogen resulted in the greatest shoot relative growth rate between the first and second harvest. Field tests, using three climate treatments (ambient, increased temperature, reduced precipitation with increased temperature) and three plant competition levels (monoculture winter wheat, monoculture B. tectorum, and biculture of the two), found that for both winter wheat and B. tectorum monocultures, ambient and warmer climates produced similar yields and biomass, respectively, whereas the drier with warmer treatment reduced these factors. Additionally, B. tectorum presence increased winter wheat grain protein. A quadratic interaction model of winter wheat yield as a function of B. tectorum biomass by climate treatment suggests that at low to moderate B. tectorum biomass levels, winter wheat yield was negatively impacted by the warmer and drier treatment, whereas ambient and warmer treatment results were similar.
Understanding mechanisms of invasion and restoring lands impacted by non-native annual grasses
(Montana State University - Bozeman, College of Agriculture, 2020) Majeski, Michelle Lynn; Chairperson, Graduate Committee: Jane M. Mangold; Catherine Zabinski, Lisa J. Rew and Jane Mangold were co-authors of the article, 'Ventenata dubia growth responds to field soil inocolum but not phosphorous and potassium treatments' which is contained within this thesis.; Catherine Zabinski, Lisa J. Rew and Jane Mangold were co-authors of the article, 'Ventenata dubia was associated with perennial grasses, bare ground and soil potassium concentration' which is contained within this thesis.; Stacy C. Simanonok, Zach Miller, Lisa J. Rew and Jane Mangold were co-authors of the article, 'Spring seeding provides a seasonal priority effect for Pseudoroegneria spicata in Bromus tectorum-invaded rangelands' which is contained within this thesis.
European settlement and development of rangelands in the western U.S. has led to a shift in vegetation from native species to introduced species, some of which have become weedy and invasive. Effects of invasive plant species can vary but often include replacing native vegetation, altering ecosystems, affecting wildlife that relied on the native plants for food and shelter, and toxicity to livestock. Two introduced annual grasses of concern are Ventenata dubia and Bromus tectorum. These grasses are at different stages in their invasion in the western U.S. Ventenata dubia is a recent invasive species in the past ten years and B. tectorum has been dominant in the Intermountain West since the mid-1900s. Three independent studies were conducted to understand characteristics of V. dubia invasion and to test whether a seasonal priority effect could be shifted to Pseudoroegneria spicata to outcompete B. tectorum in range/pasturelands. A full-factorial design was executed in a greenhouse setting to examine if a plant-soil feedback contributes to V. dubia invasion and if V. dubia preferred specific nutrients for growth. Ventenata dubia biomass, shoot height and number of leaves and tillers (per plant) were higher when grown with field soil inoculum compared to sterilized greenhouse soil. Ventenata dubia growth varied among nutrient treatments, but trended higher with a full nutrient solution. A nested observational study was conducted to examine abiotic and biotic characteristics associated with V. dubia infestations. Ventenata dubia was positively associated with non-native perennial grasses and negatively associated with native perennial grasses, bare ground/rock and soil potassium concentration. A randomized split-plot design was performed in B. tectorum-infested range and pasturelands to test whether timing of herbicide application and seeding of P. spicata could create a seasonal priority effect for P. spicata. Bromus tectorum had lower cover and biomass (per m2) with spring herbicide application. Higher P. spicata density, cover and biomass resulted with spring seeding after B. tectorum was reduced. These studies show that established and seeded native perennial grasses can compete with nonnative, invasive annual grasses. When existing management tools (herbicide and revegetation) are applied in a different way, native perennial grasses benefit.
An experimental approach to understanding how Bromus tectorum will respond to global climate change in the sagebrush-steppe
(Montana State University - Bozeman, College of Agriculture, 2016) Larson, Christian Douglas; Chairperson, Graduate Committee: Lisa J. Rew
Global climate change, including elevated atmospheric CO 2 concentrations, increases in global surface temperatures, and changes in resource availability, has significant consequences for global plant communities, one of which is the expansion of invasive species. The invasive grass species Bromus tectorum dominates areas of the North American sagebrush-steppe. In these areas, B. tectorum responds positively to elevated nutrients after fire and a positive feedback with fire has been initiated. Bromus tectorum dominance and its positive response to fire are limited by cold and moist climates. Global climate change is predicted to expand the climate suitability for B. tectorum dominance, as well as that of its response to fire. Using a field study and controlled setting experiments, I investigated this prediction. In a cold and moist southwestern Montana sagebrush-steppe, my field experiment assessed the response of B. tectorum and the native plant community to increased growing season temperatures, decreased growing season precipitation, and a prescribed burn. We found that both B. tectorum and a dominant native perennial grass, Pseudoroegneria spicata, responded negatively to experimental warming, and warming and drying. Bromus tectorum's response to fire was limited to an increase in individual fecundity across the climate scenarios and compensatory growth in warm and dry conditions. In controlled settings, using differing densities of B. tectorum and P. spicata, I performed replacement series experiments that altered temperature, water availability, nutrient availability, and, secondly, atmospheric CO 2 concentration and water availability. Bromus tectorum competitiveness was enhanced by warmer and drier conditions and elevated nutrient availability. When grown in monoculture, both species responded positively to elevated CO 2. When grown in competition, elevated CO 2 increased P. spicata's already significant suppressive effect on B. tectorum. This effect was magnified when soil moisture was limited. Due to B. tectorum's significant negative response to the field climate treatments, its limited response to fire, and the significant suppressive effect of the native grasses in both experiments, especially in elevated CO 2, I conclude that similar future climate scenarios will not promote the expansion of B. tectorum dominance and its positive response to fire within the cold and moist northern region of the sagebrush-steppe.
Evaluating non-native annual brome control with herbicides and facilitating Wyoming big sagebrush establishment in degraded drylands
(Montana State University - Bozeman, College of Agriculture, 2017) Metier, Emily Pierson; Chairperson, Graduate Committee: Lisa J. Rew; Matt Rinella (co-chair)
The degradation of drylands, through resource extraction and non-native annual brome invasion, is a major problem throughout the Intermountain West. Most restoration relies on establishing desired species from seed, but success is limited and establishing Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) is especially failure prone. This study focused on developing methods for controlling annual bromes, specifically cheatgrass (Bromus tectorum L.) and Japanese brome (Bromus japonicus Thunb.), and successfully re-introducing native sagebrush steppe species to degraded drylands. In the greenhouse, I assessed the efficacy of glyphosate and four graminicides (clethodim, sethoxydim, fluazifop, and quizalofop) applied at two rates, to cheatgrass plants of different heights. I also assessed the same five herbicides on three accessions of cheatgrass and Japanese brome. All herbicides reduced cheatgrass biomass, with most effective control on plants less than 11 cm. Overall, glyphosate and sethoxydim treatments were least effective, and quizalofop and fluazifop treatments were most effective. Japanese brome and the disturbed accessions of both species were more susceptible to herbicides than cheatgrass and the undisturbed accessions. My field study targeted the same annual bromes on two Montana coal mines. Four herbicide treatments (control, glyphosate, quizalofop, or glyphosate plus quizalofop) and two seeding treatments (differing in the amount of sagebrush seed) were evaluated for their effectiveness to manage annual bromes and boost seeded species establishment. Half of each herbicide plot was retreated with quizalofop the second year. All herbicide treatments reduced annual brome cover, especially in plots that received glyphosate. Wyoming big sagebrush density and cover of sown species increased in seeded plots with and without herbicides, but there was no difference between seeding treatments. Herbicide effects on seeded species were inconsistent, though generally establishment was greatest in plots receiving glyphosate. Quizalofop retreatment reduced annual brome cover, but did not impact seeded species establishment. These results suggest that targeted herbicide applications can be used to control non-native annual bromes and increase seeded species establishment. Specifically, using glyphosate pre-seeding when plants are small and graminicides post-seeding, can decrease annual brome cover. These treatments can provide a window of opportunity for establishing species from seed, including Wyoming big sagebrush.
Optimizing efficacy of Bromus tectorum (cheatgrass, downy brome) biological contorl in crops and rangelands
(Montana State University - Bozeman, College of Agriculture, 2017) Ehlert, Krista Ann; Chairperson, Graduate Committee: Fabian D. Menalled; Jane M. Mangold (co-chair)
Management of Bromus tectorum L., an annual grass invasive in western North America, has focused on single and integrated methods across crop and non-crop settings. Extensive literature does not exist on the integration of Pyrenophora semeniperda, a generalist grass pathogen for B. tectorum control, which has been used experimentally with some success to control B. tectorum. However, questions remain about (1) the risk of non-target effects on grassy species, (2) efficacy as part of an integrated management plan, and (3) efficacy under different environmental conditions and on different B. tectorum populations. I sought to answer these questions with three distinct studies. First, I assessed the risk of P. semeniperda on B. tectorum and 15 co-occurring grass species in a greenhouse setting. Pyrenophora semeniperda reduced B. tectorum density by 40% but also negatively affected density of 60% of the non-target species tested, particularly native rangeland grasses. Second, I integrated P. semeniperda as part of a two-year rangeland revegetation management plan that included an herbicide (imazapic), a fungicide seed treatment, and different perennial grass seeding rates. Application of P. semeniperda did not increase inoculum loads above ambient levels, and there was no effect of seeding rate or seed treatment on B. tectorum or seeded perennial grass density or biomass. However, B. tectorum density was reduced by 60% the first year with a single imazapic application. Lastly, I compared the effects of temperature (13°C, 17°C, 21°C, 25°C, 32°C) and B. tectorum populations (range, crop, sub-alpine) on infection and mortality rates caused by P. semeniperda using a temperature gradient table. Infection rates by P. semeniperda peaked at intermediate temperatures (17°C, 21°C, 25°C) for range and sub-alpine populations, but were generally low and not as influenced by temperature in the crop population. Overall, B. tectorum control with P. semeniperda is possible, provided (1) non-target effects are considered, especially for range species, (2) research is conducted to increase P. semeniperda inoculum loads above ambient levels and revegetation is used with other control tactics, and (3) we take into account how distinct B. tectorum populations respond to P. semeniperda.
Disturbance and site characteristics relate to cheatgrass (Bromus tectorum) abundance on ranches in Montana foothills ecosystems
(Montana State University - Bozeman, College of Agriculture, 2016) Ozeran, Rebecca Kathleen; Chairperson, Graduate Committee: Craig Carr
Cheatgrass (Bromus tectorum L.), also known as downy brome, is an invasive, exotic annual grass found throughout North America. Cheatgrass has been extensively studied in the Great Basin region of North America, where the majority of precipitation comes in winter and early spring, and the vegetation consists primarily of cool-season species. However, little research has been done in northern foothills grasslands in and near Montana, where most precipitation comes in spring and summer, supporting a mixture of cool- and warm-season plant species. Climate and vegetation differ between the northern foothills grasslands and the Great Basin, so the ecological impacts of cheatgrass in the northern foothills grasslands are unknown. In order to better understand cheatgrass ecology in this region, we assessed cheatgrass abundance in foothills ecosystems in Montana. Fifteen study plots were established at each of two ranches in Montana, both of which are owned and operated by the Montana Agricultural Experiment Station: Thackeray Ranch, southeast of Havre, Montana, and Red Bluff Ranch, east of Norris, Montana. At these plots we examined relationships among cheatgrass abundance, biotic and abiotic site characteristics (e.g. species diversity, soil depth), and disturbance indicators (e.g. livestock fecal counts) in 2014 and 2015. Large generalized linear mixed-effects regression models for each ranch were reduced to simpler models by comparing the Aikake's Information Criterion (AIC) for each fitted model, and selecting for lower AIC to best describe cheatgrass abundance. Multimodel inference based on the best models for each ranch identified important variables to predict cheatgrass abundance. Disturbance and site characteristics such as aspect and soil texture are important predictors that land managers in the northern foothills grasslands could monitor to estimate the risk of cheatgrass invasion or dominance on the landscapes they manage.
Geographical analysis of the distribution and spread of invasive plants in the Gardiner Basin, Montana
(Montana State University - Bozeman, College of Letters & Science, 2003) Rens, Emily Nicole
Cheatgrass invasion of sagebrush steppe : impacts of vegetation structure on small mammals
(Montana State University - Bozeman, College of Letters & Science, 2014) Bachen, Daniel Allen; Chairperson, Graduate Committee: Andrea Litt; Andrea R. Litt and Claire Gower were co-authors of the article, 'Effects of cheatgrass invasion on food accessibility for small mammals in sagebrush steppe' submitted to the journal 'Journal of wildlife management' which is contained within this thesis.; Andrea R. Litt and Claire Gower were co-authors of the article, 'Changes in predation risk for deer mice (Peromyscus maniculatus) with plant invasions: understanding mechanisms' submitted to the journal 'Journal of wildlife management' which is contained within this thesis.
Nonnative plants can affect habitat quality for native animals directly, through changes in resources like cover or food, and indirectly, through changes in access to resources or predation risk. Understanding these effects is crucial to develop management techniques and maintain ecosystem processes. In sagebrush steppe, brome grasses such as cheatgrass (Bromus tectorum) can invade and form dense stands, increasing the depth and persistence of litter, as well as the density of standing vegetation. These structural changes alter abundance and composition of the small mammal community. We used a series of experiments to explore whether changes in vegetation structure associated with the invasion of cheatgrass would alter foraging and predation risk of small mammals, to better understand mechanisms driving documented population- and community-level effects. In the first experiment, we placed a measured amount of grain at stations with either increased litter or stem density, and examined how much grain was removed nightly. We found that adding litter reduced the amount of grain removed in 2 of our 3 study areas. In the second experiment, we timed animals fleeing a simulated predator through various depths of litter or densities of stems. We found that dense stems impeded movement more than litter. In the third experiment, we recorded animals moving through native sagebrush steppe and cheatgrass monocultures, and analyzed these recordings to detect differences in the volume of noise created, especially for frequencies detected by common predators. We found that animals moving through cheatgrass made more noise at high frequencies, compared to native sagebrush steppe. Based on these experiments, cheatgrass monocultures may reduce habitat quality for small mammals by decreasing foraging efficiency and increasing vulnerability to predators. Mitigation strategies should focus on reducing the density of standing vegetation where predation is a limiting factor and litter depth where small mammals are food-limited.
Enhancing efficacy of herbicides to control cheatgrass on Montana range, pasture, and Conservation Reserve Program (CRP)
(Montana State University - Bozeman, College of Agriculture, 2013) Ehlert, Krista Ann; Co-chairs, Graduate Committee: Jane M. Mangold and Richard E. Engel
Chemical control of cheatgrass has recently focused on imazapic; factors such as application rate and timing and the presence of plant litter can influence imazapic's efficacy. Herbicides minimally impact the seedbank so integrating a seed-killing pathogen like Pyrenophora semeniperda may result in more effective and sustainable control. My research objectives were to 1) test the effect of imazapic application rate and timing and plant litter on cheatgrass and desired plant species in range and Conservation Reserve Program (CRP) lands, 2) conduct a soil bioassay to determine imazapic persistence as affected by imazapic rate, presence of plant litter, and time after herbicide application, and 3) determine whether the fungal pathogen P. semeniperda combined with a single imazapic application would provide greater control of cheatgrass than either strategy used alone. Objective 1 was carried out in range and CRP lands over two years with a factorial combination of four imazapic rates, two litter manipulation treatments and/or two application timings. In general, all three imazapic rates were equally effective in controlling cheatgrass compared to the non-sprayed control. Litter manipulation treatments had little effect on imazapic efficacy, but early application of imazapic resulted in more consistent cheatgrass control. Objective 2 was conducted in the greenhouse using soil samples collected over a six month period from the field study for Objective 1. Cucumber and cheatgrass were used as indicator species. All three herbicide rates reduced both species' biomass below that of the control. Again, litter manipulation had a minimal effect, and imazapic was found to persist through the following spring after spraying. Objective 3 was explored in a greenhouse experiment using a factorial combination of two imazapic treatments, two P. semeniperda treatments, and three seeding depths. Pyrenophora semeniperda reduced cheatgrass emergence, while cheatgrass biomass and density were affected by imazapic and the integration of imazapic and P. semeniperda. Imazapic and P. semeniperda did not favorably interact to reduce biomass and density; however, integrating these two tools holds promise as P. semeniperda can reduce the seedbank, and imazapic can control seedlings that escape pathogen-caused mortality.
Understanding ecological interactions to improve management of Bromus tectorum in rangeland and cropland ecosystems
(Montana State University - Bozeman, College of Agriculture, 2011) Orloff, Lesley Noelle; Chairperson, Graduate Committee: Jane M. Mangold; Fabian D. Menalled (co-chair)
Bromus tectorum L. (downy brome or cheatgrass) has been called the most dominant invasive plant species in the western United States. It is a barrier to restoration efforts in degraded lands and a serious weed problem for small grain growers. Investigating ecological interactions that play a mechanistic role in its success is a necessary step towards developing effective ecologically-based management strategies for B. tectorum. We investigated how biotic and abiotic factors impact interactions between B. tectorum and desired vegetation, with implications for restoration of lands dominated by B. tectorum and management of B. tectorum in small-grain cropping systems. Our research objectives were; 1) appraise the impact of relative size and soil nitrogen (N) availability on interactions between B. tectorum and Pseudoroegneria spicata (Pursh) A. Love (bluebunch wheatgrass), a species important in rangeland revegetation, and, 2) determine the impacts of Wheat streak mosaic virus (WSMV), resource availability, and neighborhood characteristics on B. tectorum performance in a winter wheat (Triticum aestivum L.) system. Objective 1 was carried out in a greenhouse experiment with two trials, following an addition series factorial design with four density treatments for each species, three P. spicata size cohort treatments, and two N treatments. Regression analysis indicated that giving P. spicata an initial size advantage over B. tectorum increased its ability to both suppress and avoid suppression by B. tectorum. We also observed that while N availability increased productivity of both species, it did not change their competitive relationship. Objective 2 was explored in two trials of a field experiment using a split-plot design with N availability assigned to main plots, WSMV inoculation assigned to subplots, B. tectorum proximity to the nearest wheat row as a predictor, and neighborhood characteristics as covariates. Regression analysis indicated that in low and high N environments (compared to the recommended N rate), distance from row influenced individual B. tectorum biomass only in disease-free environments, suggesting that healthy wheat suppressed B. tectorum that was closest to the row. Wheat inoculated with WSMV did not suppress B. tectorum. In an intermediate N environment, increased distance from row increased B. tectorum performance only with WSMV inoculation.

Theses and Dissertations at Montana State University (MSU)

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