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.

The overall aim of the research project was to evaluate the potential of the fungal pathogen <I>Ascochyta caulina</I> as a biological control agent against <I>Chenopodium album</I>, a major weed in arable crops. A number of isolates of <I>Ascochyta caulina</I> were evaluated but isolate W 90-1 from Holland proved to be the most promising candidate because of its high virulence. It was therefore selected for more detailed greenhouse and field studies into the environmental parameters required for infection and disease development. Results of these studies showed that in order to achieve the maximum infection, a temperature of between 20-30°C, a relative humidity of >95% for 24 h and a spore density of approximately of 1-2 x 10⁶ spores per ml spore suspension were required. Mortality and plant necrosis levels after application of <I>A. caulina</I> decreased with plant age and treatment of <I>C. album</I> shortly after emergence or to juvenile plants (before 4-leaf growth stage) was most effective. The requirement for long periods of high relative humidity and the inability of <I>A. caulina </I>to cause satisfactory disease after the 4 leaf growth stage are the most important limiting factors for the development of <I>A. caulina</I> as a bioherbicide for <I>C. album. </I>A range of spore formulations was studied with the aim of reducing the requirement for long periods of high relative humidity for disease development. Studies indicated that disease development could be increased by incorporation of surfactants (Tween 80 or Sylgard) and nutrients (Czapek-Dox Broth and Yeast Extract) into inoculum suspension. Results of field trials indicated that if application were properly timed and optimum environmental conditions can be achieved the pathogen can give satisfactory control of the weed.

Successful weed control is essential for economical cotton production in Uganda. Weeds compete with cotton for moisture, nutrients and light. The greatest competition usually occurs early in the growing season. Therefore, post emergence herbicides such as fluazifop-butyl and sethoxydim were used in this study to control the grass weed species which grow faster than cotton during its initial growth stage. Field trials were conducted on the sandy loam/loam soils at Namulonge Research Institute and Bukalasa Technology Verification Centre in Uganda during the 1995/96 and 1997/98 cotton seasons to investigate the control of the tropical couch grass (Digitaria abyssinica (A. Rich. ) Stapf) using the post emergence herbicides. This weed is a rhizomatous grass and difficult to control. The efficacy of the reduced dose rates of the grass selective post emergence herbicides sethoxydim and fluazifop-butyl was investigated for the control of D. abyssinica and other grass weed species in cotton so as to determine the appropriate dose rate(s). The herbicides were supplemented with two hand weedings. Hand weeding (5 times) during the growing season was included in the treatments. The results obtained from the field trials showed the potential of reduced dose rates in the control of grasses. The application of fluazifop-butyl (138,162 and 188 g a. i. ha 1) and sethoxydim (405,502 and 579 g a. i. ha 1) gave a significant density reduction of D. abyssinica and other annual grasses at 35 days after herbicide application. No significant differences were observed amongst the dose rates of both herbicides in the percentage weed control of D. abyssinica and other grass weed species in the two seasons. The percentage weed control ranged between 79-96%. The assessment showed that fresh and dry weights of D. abyssinica shoots/foliage were reduced by 70-80% irrespective of the dose rates for both herbicides at the two sites during the two seasons. Reduced dose rates below half of the full dose rates were investigated in the greenhouse in UK. A markedly reduction of D. abyssinica shoots and rhizomes was noted following the application of fluazifop-butyl (38,66,94,188 g a. i. ha 1) and sethoxydim (116,203, 290,579 g a. i. ha 1) compared to the control. An average percentage reduction of 43.2- 62% for fresh and dry shoots, and 65.9-78% for fresh and dry rhizomes was observed. Although analysis of variance indicated that there were no significant differences amongst dose rates, low percentage reduction was noted from the lowest dose rate of fluazifopbutyl (38 g a. i. ha 1). 1 As part of the plant stress assessment, results indicated that sethoxydim and fluazifopbutyl inhibited chlorophyll accumulation in the treated leaves of D. abyssinica. A reduction of 40-70% of chlorophyll content was noted. It was noted that sethoxydim had higher inhibitory effect on chlorophyll content than fluazifop-butyl. Results obtained from the measurements of fluorescence parameters showed significant reduction of Fv/Fm in the leaves of D. abyssinica due to sethoxydim and fluazifop-butyl, suggesting significant alteration of the normal fluorescence yield. Interference with the normal fluorescence of D. abyssinica was associated with the inhibition of the flow of electron transport which resulted to plant stress. Further investigation on plant stress was studied by comparing the activity levels of the intracellular proteases of D. abyssinica and cotton plants after the application of sethoxydim. The activity level of alanyl aminopeptidase was not affected by the herbicide both in D. abyssinica and cotton. It was however noted that there was significant decrease in the activity levels of argninyl aminopeptidase (arginyl-ap) (36.1%) and tripeptidyl aminopeptidase (Tap) (51.8%) in the treated plants of D. abyssinica with time after herbicide application. While in cotton, significant increase was observed in the activity level of and tripeptidyl aminopeptidase with time after herbicide application. Therefore it can be assumed that the activity levels of these enzymes in the two plant species may have an influence on their responses to the herbicide. Data on crop performance indicated that seedcotton yields realised from herbicides dose rates combined with two hand weedings were high as or higher than the yields obtained from the hand weeding (5 times). Seedcotton yields were noted high (1793-2993 kg/ha) in 1995/96 compared to 1997/98 (665.1-1184.2 kg/ha). The present study has indicated that integration of reduced dose rates with two hand weeding supplements can reduce the number of weedings and improve cotton production.

No description available.

Field experiments were conducted from 1989 to 1991 to evaluate several sulfonylurea herbicides, glyphosate and clopyralid for the control of bunchberry and other hexazinone tolerant weeds in lowbush blueberry. Broadcast applications of chlorosulfuron, metsulfuron and glyphosate reduced bunchberry densities at all application dates, though crop damage and subsequent yield reductions were unacceptable. Glyphosate was very effective in controlling a large number of plant species when applied as a spot spray treatment. Tribenuron and DPX R9674 were effective in suppressing bunchberry stem densities at all application dates, without major adverse effects on blueberry, and also controlled a large number of hexazinone tolerant weeds when applied as a spot spray treatment. Clopyralid, at rates as low as 100 g a.i. ha$ sp{-1}$, was very effective as a broadcast treatment for the control of tufted vetch, although problems with crop tolerance and yield reductions were evident in some instances. Clopyralid did not control a large number of hexazinone tolerant species when applied as a spot spray treatment.

Two field studies assessed sward dynamics to legume removal with and without Canada thistle and other broadleaf plants (i.e. forbs). When grown in mixtures with grass, alfalfa had a more consistent negative yield response to legume removal compared to clover swards. Within established pastures, total forage (i.e. legume and grass) had little association with Canada thistle, but was instead associated with perennial forbs such as dandelion. Grass responses (biomass and protein yield) in established swards were unable to compensate for legume removal up to 2 years after spraying. Relative yield ratios were used to identify weed and legume thresholds, and indicated the removal of legume and Canada thistle did not always negatively impact forage production. Instead, select positive yield responses were observed depending on the initial composition, growing conditions and abundance of weed and legume. / Rangeland and Wildlife Resources

Thesis (M.A.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Nov. 5, 2008). Includes bibliographical references (p. 39-42).

No description available.

The popularity of growers using only postemergence (POST) herbicides for weed management in soybean was enabled by the commercialization of glyphosate-resistant soybean. The efficacy and flexibility provided by this technology diminished the use of soil residual herbicides and arguably, increased soybean yield loss from early-season weed competition. While, the rapid evolution and biogeographical spread of herbicide-resistant weeds, especially glyphosate-resistant biotypes, has renewed interest into the use of soil residual products, herbicide-resistant soybean technologies continue to be developed that may once again entice growers into POST-only weed management systems. The commercial interest in soybean yield advancements justifies further characterizing the benefits provided by early-season weed control beyond those of herbicide-resistance management. Furthermore, as awareness heightens regarding techniques that will enhance the sustainability of agro-ecosystems, specific focus on resource utilization will help to evaluate the viability of this weed management strategy. Field experiments were conducted across four sites throughout southern Illinois in 2012 and 2013 to study the influence of early-season weed management strategies on soybean nutrient accumulation, grain yield parameters, and the acquisition of nutrients by broadleaved and grass weeds. Increasing periods of weed competition duration were established by removing weeds at heights of 10, 20, 30 or 45 cm with glyphosate. A weed-free treatment utilizing a comprehensive soil residual and POST herbicide program was included to implement a weed-free comparison. Two standard herbicide management strategies that simulate common grower practices were also evaluated for comparison: flumioxazin PRE followed by glyphosate POST and two sequential POST glyphosate applications. Averaged across all 11 mineral nutrients analyzed in this experiment, broadleaved weeds accumulated 149 and 108% more nutrients than grasses in 2012 and 2013, respectively. Competition from 20-cm weeds reduced the acquisition of N, P, Ca, Mg, S, Fe, B, Cu, and Zn by soybean in 2012; these nutrients in addition to K and Mn were reduced by the same level of competition in 2013. N and Fe were the nutrients in soybean most notably impacted by weed interference. Reductions in soybean grain yield were the result of competition with 30-cm weeds in 2012, and 10-cm weeds in 2013; while, both standard herbicide regimens yielded less than the weed-free treatment in 2013 only. Additionally in 2013, average soybean seed weight and grain oil content was reduced when weeds were not removed before a height of 10 and 20 cm, respectively. The rate of decomposition and nutrient release was measured for waterhemp and giant foxtail desiccated by glyphosate at heights of 10, 20, 30, and 45 cm in two southern Illinois soybean fields. Weed biomass was grown under greenhouse conditions to ensure homogeneity and litterbag methodology was utilized to track in situ mass and nutrient losses, expressed as a decay constant (k) regressed over time according to the single exponential decay model. The effect of specie and height both had a strong influence on the intrinsic properties of the weed biomass and the associated rate of decay. Concentrations of the recalcitrant cell wall components (cellulose, hemicellulose, and lignin) were generally greatest as weed height (plant age and development) increased and with giant foxtail compared with waterhemp. Ca, Mg, and S concentrations were greater in waterhemp, while N was greater in giant foxtail. N and K concentrations decreased with increasing weed height. After 16 weeks, 10-cm waterhemp and giant foxtail detritus had lost 10 and 12% more mass compared to the 45-cm height. Decomposition rates revealed mass loss was highest for 10-cm waterhemp (kD = 0.022) and lowest for 45-cm giant foxtail (kD = 0.011) and this process was negatively correlated to the overall amount of cell wall constituents (r = -0.73). Nutrient release rates followed a similar trend in that shorter (younger) weeds and waterhemp liberated nutrients more readily. Across all tested plant material, K was the nutrient most rapidly released, whereas, Ca was the most strongly retained nutrient. Although the pressing challenge of managing herbicide-resistant weeds justifies the implementation of early-season weed control tactics, this research suggests there are ancillary benefits that are provided by this strategy. The use of a robust, broad-spectrum soil residual herbicide program in conjunction with timely POST applications provides the foundation for early-season weed management, thereby minimizing non-crop nutrient use and enhancing the nutrient acquisition capacity in soybean. This strategy facilitates more sustainable crop production by requiring fewer supplemental nutritional inputs while also protecting grain yield.

Made available in DSpace on 2014-06-11T19:29:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-02-28Bitstream added on 2014-06-13T18:39:27Z : No. of bitstreams: 1 paula_cs_me_ilha.pdf: 334753 bytes, checksum: fcd8aee2a013e0a21c4a8de75c837120 (MD5) / A ocorrência de plantas daninhas em pastagens é um dos fatores responsáveis pela queda na produtividade das plantas forrageiras e, a espécie Mimosa pudica L. (malícia) é uma das mais frequentes infestantes na região centro-oeste brasileira. O trabalho constou de dois experimentos e foi desenvolvido com o objetivo de analisar a eficácia de herbicidas hormonais recomendados para pastagens, no controle de M. pudica, considerando as doses normais e doses reduzidas dos herbicidas. O primeiro experimento foi desenvolvido no município de Inocência, MS, onde o trabalho foi realizado em campo sobre a forrageira Brachiaria decumbens Stapf, analisando-se os dados submetidos aos tratamentos sob o aspectos de eficácia. Os tratamentos utilizados foram: 2,4-D + picloran (2,0; 3,0 e 4,0 L/ha), fluroxypyr + picloran (1,0 e 2,0 L/ha), aminopiralide + 2,4-D (1,0 e 2,0 L/ha), aminopiralide + fluxipir metílico (0,5 e 1,0 L/ha), 2,4-D (2,0 L/ha) e testemunha sem herbicida. O segundo experimento foi desenvolvido em laboratório no município de Ilha Solteira, SP, onde o trabalho foi realizado em laboratório e os herbicidas foram aplicados sobre a espécie daninha M. pudica cultivada em vasos. Os tratamentos para esta fase foram os seguintes: 2,4-D + picloran (2,0; 3,0 e 4,0 L/ha), fluroxypyr + picloran (1,0 e 2,0 L/ha), aminopiralide + 2,4-D (1,0 e 2,0 L/ha) e aminopiralide + fluxipir metílico (0,5 e 2,0 L/ha). Neste experimento analisou-se também o efeito dos tratamentos sobre as plantas daninhas em relação à sua sensibilidade ao toque e em relação à taxa de ETR (taxa de caminhamento de elétrons) utilizando-se um fluorômetro. Observou-se que, no primeiro experimento, todos os tratamentos, exceto o 2,4-D isolado, controlaram eficazmente a planta daninha. No segundo experimento, os tratamentos utilizados controlaram 100% a planta daninha... / The occurrence of weeds in pastures is one of the factors responsible for the decline in productivity of forage plants and the species Mimosa pudica l. (malice) is one of the most common weeds in the central-western Brazil. The study consisted of two experiments and was developed with the aim of analyzing the efficacy of hormonal herbicides recommended for pastures to control M. pudica, considering the normal doses and low doses of herbicides. The first experiment was conducted in the municipality of Inocência, MS, where the field work was carried out on the grass Brachiaria decumbens analyzing treatments under the aspects of efficacy. The treatments for this step were as follows: 2,4-d + picloran (2.0, 3.0 and 4.0 L / ha) + fluroxypyr picloran (1.0 and 2.0 l / ha), aminopyralid + 2,4-D (1.0 and 2.0 L / ha) + aminopyralid fluxipir methyl ester (0.5 and 2.0 L/ ha), 2,4-D (2.0 L / ha) and witnesses in the bush and clean. The second experiment was conducted in single Ilha Solteira, SP, where the work was performed in the laboratory and were sprayed on the weed M. Pudica cultivated in pots. The treatments for this step were as follows: 2,4-D + picloran (2.0, 3.0 and 4.0 L / ha) + fluroxypyr picloran (1.0 and 2.0 L/ ha), aminopyralid + 2,4-D (1.0 and 2.0 L / ha) + aminopyralid and fluxipir methyl ester (0.5 and 1.0 L / ha). This experiment also examined the effect of treatments on weeds in relation to their sensitivity to touch and relative to ETR rate (rate of traversal of electrons) using a fluorometer apparatus. It was observed that in the first experiment, all treatments except 2,4-D alone, effectively controlled the weed. In the second experiment, the treatments used 100% controlled the weed and no differences in the rate of ETR and sensitivity to touch, to 3 days after application. It was also found that lower dose in all treatments that... (Complete abstract click electronic access below)