Limitations to broadleaf weed management options in chickpea present obstacles for stable production. Even with low weed incidence, chickpea yield can be severely affected, creating need for an integrated weed management system. Due to zero-tillage commonly practiced in Saskatchewan, there is heavy reliance on herbicides. The chickpea breeding program at the Crop Development Centre, University of Saskatchewan, has developed chickpea cultivars with resistance to imidazolinone (IMI) class of herbicides. The objectives of this study were: (i) to examine the reaction of four chickpea cultivars – CDC Luna, CDC Corinne, CDC Alma, and CDC Cory - to imazamox, imazethapyr, and a combination of imazamox and imazethapyr under field conditions; and (ii) to examine cultivar responses to IMI applications at different growth stages: 2-4 node, 5-8 node, and 9-12 node stage. Field experiments were conducted over five site years in Saskatchewan, Canada in 2012 and 2013. For each experiment, visual injury ratings, plant height, node, and internode length were recorded at 7, 14, 21, and 28 days after each herbicide application (DAA). Days to flowering (DTF), days to maturity (DTM), number of primary branches, pods per plant, harvest index, and seed yield were additional measurements for elucidating physiological responses. Conventional cultivars, CDC Luna and CDC Corinne, had moderate to severe visual injury scores compared to resistant cultivars, CDC Alma and CDC Cory, with minimal to no visual injury after IMI treatment. Height stopped increasing and node development slowed for conventional cultivars treated with IMI herbicides. This susceptibility to IMI herbicides was also recognized with a delay in the DTF and DTM. Despite significant negative response, CDC Luna and CDC Corinne were able to recover throughout the field season, resulting in no yield loss from IMI treatments. Resistant cultivars CDC Alma and CDC Cory demonstrated no negative response from IMI herbicide application compared with the untreated controls. Growth, in terms of height and node development, DTF, DTM, and yield were not significantly different between IMI treated and control treatments. Resistant cultivars tolerated IMI herbicide at all growth stages tested. These results demonstrate potential for use of IMI herbicides in chickpea, expanding the currently limited options for broadleaf weed control.

Weed control is a critical component in pastures and hayfields in order to ensure maximum forage yields. Typically, broadleaf weed control in pastures and hayfields is achieved through the use of synthetic auxin. However, these herbicides also control desirable broadleaf species such as forage legumes, including white clover. Use of herbicides can lead to severe injury and often complete elimination of white clover, making it difficult for producers to maintain legumes in mixed grass-legume swards while controlling weeds. It is often desirable to have legumes present in the sward due to their high nutritive forage value and ability to fix nitrogen compared to grass only swards. Florpyrauxifen-benzyl + 2,4-D is a new herbicide which is reported to control broadleaf weed species, while preserving white clover. Little published research exists on this herbicide, particularly for use in pastures and hayfields. Research evaluating sward composition indicates that florpyrauxifen-benzyl + 2,4-D is effective in controlling broadleaf weed species while also preserving greater amounts of white clover than any other herbicide treatments. Florpyrauxifen-benzyl + 2,4-D also resulted in significantly more forage grass production than the nontreated control. Florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides when applied via fertilizer impregnation. Additional research assessing the spectrum of broadleaf weed control found that florpyrauxifen-benzyl + 2,4-D is a viable herbicide for the control of several broadleaf weed species including bulbous buttercup, Canada thistle, broadleaf plantain, plumeless thistle, and common ragweed. However, florpyrauxifen-benzyl + 2,4-D was less effective than other herbicides for controlling certain weeds, such as horsenettle. White clover was injured from florpyrauxifen-benzyl + 2,4-D, but was able to fully recover in 90 to 120 days. There were no differences in white clover response between the four varieties tested. When evaluating establishment of forage species, florpyrauxifen-benzyl + 2,4-D did not injure or reduce biomass of tall fescue or orchardgrass plantings, indicating a high level of safety. Florpyrauxifen-benzyl + 2,4-D was also safe to both drilled and frost seeded clover when applied prior to and at planting. Greenhouse trials revealed that flowering white clover is more sensitive to herbicides compared to vegetative white clover, and that safety of white clover to florpyrauxifen-benzyl + 2,4-D is dependent upon use rate. Considerations such as weed species present, and the amount of white clover injury that is considered acceptable will dictate the decision to utilize florpyrauxifen-benzyl + 2,4-D in pastures and hayfields. This research demonstrates the effectiveness and overall utility of florpyrauxifen-benzyl + 2,4-D for use in pastures and hayfields due to the effectiveness of weed species as well as the level of safety to white clover. / Doctor of Philosophy / Pastures and hayfields are a critical component in livestock production. Grazing livestock perform best on highly nutritious forages. Legumes such as white clover are highly nutritious in forage systems and offer other benefits such as the ability to fixate nitrogen. Conversely, weed species negatively impact forage production by competing for resources with desirable forage species. Additionally, many species of broadleaf weeds are toxic to livestock. Because grasses are the backbone of forage systems, the majority of weed control efforts are aimed at controlling broadleaf weed species. However, beneficial forage legumes such as white clover are susceptible to broadleaf herbicides commonly used. This creates a management dilemma for producers who wish to control troublesome weeds, but also have white clover present in their pastures and hayfields. Florpyrauxifen-benzyl + 2,4-D is a herbicide combination which is new for pastures and hayfields. This herbicide is reported to control broadleaf weeds while also preserving white clover. Research trials were conducted in order to determine if florpyrauxifen-benzyl + 2,4-D could be used in forage systems to control weeds, without killing white clover. Several research trials were established to evaluate florpyrauxifen-benzyl + 2,4-D for broadleaf weed control and white clover safety. Research trials were established to determine the effect of florpyrauxifen-benzyl + 2,4-D on the number and overall amount of forage produced and the proportion of weeds and desirable forages as affected by herbicide treatment. Florpyrauxifen-benzyl + 2,4-D resulted in a 140% increase in forage grass production, and more legume production than any other herbicide treatment, while also decreasing the quantity and amount of broadleaf weed species. Because there is little existing research on what weed species florpyrauxifen-benzyl + 2,4-D controls, research trials were established to determine the spectrum of weed species that florpyrauxifen-benzyl + 2,4-D controls. Greenhouse trials were also established to evaluate the effect of white clover variety on injury from herbicide. Results showed that florpyrauxifen-benzyl + 2,4-D is effective in controlling several weeds such as bulbous buttercup, Canada thistle, broadleaf plantain, plumeless thistle, and common ragweed. Greenhouse trials showed that white clover variety did not influence the level of injury from herbicide applications. Seedling forages are more vulnerable to weed competition and therefore weed control around the time of planting is critical. However, seedlings are typically very sensitive to herbicides, compared to mature plants. Research trials were established to determine the effect of florpyrauxifen-benzyl + 2,4-D on the establishment of forage grasses tall fescue and orchardgrass, as well as white clover. White clover was established using two commonly used methods: drilling and frost-seeding. Results from the field show that florpyrauxifen-benzyl + 2,4-D is safe use around the time of tall fescue and orchardgrass establishment, as well as white clover planting with either method. Greenhouse trials were also established to determine if white clover's growth stage at the time of herbicide application influences the response. Results show that white clover is more sensitive to herbicides applied to flowering white clover compared to vegetative growth and the level of injury is dependent upon herbicide rate. Overall, our results demonstrate the utility of florpyrauxifen-benzyl + 2,4-D for forage production by controlling weed species and being safer to white clover than commonly used herbicides.