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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 Defoliation effects on Spotted Knapweed seed production and viability(Montana State University - Bozeman, College of Agriculture, 2008) Benzel, Katie Rebecca; Chairperson, Graduate Committee: Jeffrey C. Mosley; Tracy K. Brewer (co-chair)Spotted knapweed (Centaurea stoebe L.) is a deeply taprooted perennial forb infesting millions of hectares of rangeland in western North America. Spotted knapweed forms large monocultures, which lowers plant diversity, reduces livestock and wildlife forage, and increases surface water runoff and sediment yield. It can produce 5,000-40,000 seeds m-2 year-1, and often produces new flowers after prescribed sheep grazing or mowing defoliates spotted knapweed plants during the bolting or flowering stage. Research has yet to determine if new flowers produced following spring/summer defoliation produce viable seeds by the end of the growing season. The purpose of this 2-year study was to determine the appropriate timing(s) or combination(s) of timings of defoliation on spotted knapweed to reduce viable seed production. Ten spotted knapweed plants, located on spotted knapweed-infested rangeland in west-central Montana, were hand-clipped for each of the following treatments: 1) 35-40% relative utilization of above-ground biomass when plants were in the bolting stage; 2) 100% of buds removed at late-bud/early-flowering stage; 3) 100% of flowers removed at full-flowering stage; 4) Treatment 1+Treatment 2; 5) Treatment 1+Treatment 3; 6) Treatment 2+Treatment 3; 7) Treatment 1+Treatment 2+Treatment 3; and 8) unclipped control. The number of buds/flowerheads per plant, number of seeds per plant, percent viability of seeds, and number of viable seeds per plant were determined when seeds were in the well-developed stage, but seedhead bracts were still tightly closed (mid-August through September). Clipping at any timing or combination of timings reduced the number of buds/flowerheads per plant (P < 0.01), number of seeds per plant (P < 0.01), percent viability of seeds (P < 0.01), and number of viable seeds per plant (P < 0.01) both years compared with the unclipped control. Clipping during the bolting stage reduced the number of viable seeds by nearly 90% compared with no clipping. Clipping during the late-bud/early-flower or full-flower stage reduced the number of viable seeds by nearly 100% compared with no clipping. Defoliation of spotted knapweed via prescribed sheep grazing or mowing in summer should effectively suppress viable seed production of spotted knapweed.Item Establishment and seed production of native forbs used in restoration(Montana State University - Bozeman, College of Agriculture, 2009) Wiese, Jessica Linsay; Chairperson, Graduate Committee: Fabian D. Menalled.The importance of incorporating native wildflowers into seed mixtures for disturbed land revegetation projects is widely known and accepted. However, further assessment of weed management approaches is a necessary step to successfully establish and produce native wildflower seed. We examined the impact of pre and post-emergence herbicides alone and in combination with hand weeding on 5 wildflower species [slender white prairie clover (Dalea candida(Michx). ex Willd), blanketflower (Gaillardia aristata Pursh), fuzzy tongue penstemon (Penstemon eriantherus Pursh var. eriantherus), silverleaf phacelia (Phacelia hastata Douglas ex Lehm.), and prairie coneflower (Ratibida columnifera (Nutt.) Woot. & Standl)] under greenhouse and field conditions. Herbicides evaluated included Treflan (trifluralin) 189 l/ha, Lorox (linuron) 1.121 kg/ha., Permit (halsulfuron) 91 g/ha., Plateau (imazapic) 560 g/ha, and Prowl (pendimethalin) 4.2 l/ha. The objectives of this study were to 1) determine wildflower seedling tolerance to post-emergence herbicides, 2) evaluate the effect of pre-and post-emergence herbicides on native wildflower seedling establishment, weed control, and wildflower seed production. For objective 1 a randomized block design was used and repeated twice. A Monte Carlo resampling assessed herbicide damage and a randomized block design analysis of variance (ANOVA) assessed herbicide impact on fresh and dry biomass. Results indicated that the D. candida and R. columnifera were minimally affected by herbicide treatments, while G. aristata and P. hastata were strongly affected, the first by linuron and halosulfuron and the last by halosulfuron and imazapic. Objective 2 assessed hand weeding and pre and postemergence herbicide effects on native wildflowers. A randomized block design was used to assess wildflower establishment, percentage cover, yield, and seed germination and viability, along with weed community composition and cover as a function of weed management approach. Data were analyzed with a randomized block design analysis of variance (ANOVA) to test for differences in wildflowers seedling emergence, percent cover of wildflowers, and seed yield. Wildflower species responded uniquely to weed management, indicating caution should be used when applying herbicides to the tested species. Specifically, emergence of P. eriantherus, D. candida and P. hastata were negatively affected by trifluralin, indicating this herbicide may not be suited for the tested wildflowers.