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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.