In recent years global concern over the development of herbicide resistant (HR) weeds has lead to interest in integrated weed management (IWM) strategies. IWM seeks to relieve selection pressure for herbicide resistance by utilizing mechanical and cultural controls in addition to herbicides. The situation experienced by Saskatchewan lentil growers with large populations of group 2 herbicide resistant wild mustard provides an ideal model system to test our hypothesis that IWM strategies can provide robust weed management and maintain crop yields. The first study evaluated an IWM method targeting HR wild mustard in lentil. This study was conducted for 3 years between 2011 and 2013 at 2 locations at Saskatoon and Scott, Saskatchewan. It was a randomized two way factorial with weed control method and seeding rate as the main effects. Weed control treatments tested consisted of a control treated with a glyphosate burnoff, saflufenacil (Heat ™) herbicide, rotary hoeing, half rate metribuzin (Sencor ™) herbicide, a fully integrated treatment, and a full herbicide treatment. Three seeding rates representing 1, 2, and 4 times the recommended seeding rate were tested. The integrated treatment relied on increased seeding rate to reduce mustard biomass and produce yield, and at the highest seeding rate it was able to provide equivalent yield to the full herbicide system. The results of this study show that an integrated system utilizing an increased seeding rate can control resistant weeds and maintain yields to a similar level as a strategy that relies only on herbicides for weed control. The cultural practice of increasing crop seeding rate has been identified as having potential to provide non-chemical weed control and enhance the effects of herbicide application. The objective of the second study was to examine the interaction between increasing seeding rate and the dose response relationship of weeds to herbicide application. The experiment was a factorial design with four levels of lentil seeding rate and seven levels of fluthiacet-methyl herbicide application rate. The study was conducted at two locations near Saskatoon, Sk. in 2012 and 2013. Results of the experiment show that increasing lentil seeding rate decreased the total mustard biomass when herbicides were not applied or were applied at low rates. In addition increasing lentil seeding rate lowered the herbicide dose required to result in a 50% reduction in mustard biomass in 2012, though it had little effect in 2013. These results suggest that the practice of increasing seeding rate can work with herbicide application to reliably and effectively control weeds, even in situations where herbicides alone may not achieve good control.

Cogongrass management generally requires multiple herbicide applications, however, success is limited if not integrated with other methods. Experiments were conducted to evaluate the use of cover cropping systems with herbicides on cogongrass control. Field studies determined that sequential glyphosate applications in the summer were necessary to achieve 80% or greater control, but a single application could be effective if weather conditions allowed early planting and good cover crop establishment of Roundup Ready soybeans. Studies also indicated that the use of ALS-resistant Italian ryegrass and white clover crop combinations showed no effect, but imazapyr applications made in May or June provided 80% or higher control by October. Greenhouse experiments showed that delayed planting at least 1 month after imazapyr preemergence applications from 70 to 280 g ae ha-1, significantly reduced emergence failure, height and biomass reductions of legumes used for revegetation.

Harvest weed seed controls (HWSC) destroy weed seeds that are retained by the plant at crop harvest, which would typically be spread by the harvester along with other field residues. HWSC exploits coincidental maturity between crops and weeds, so an experiment was designed to collect weed seeds as they shatter throughout the growing season and through a simulated harvest delay. This experiment monitored four economically important broadleaf species and two grass species in a soybean (Glycine max (L.) Merr.) field. Results indicated that broadleaf species shattered seed at rates accelerating through the growing season, while grass species shattered more seed early in the growing season. Field experiments in organic and conventional winter wheat (Triticum aestivum L.) fields infested with Italian ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) compared two HWSC techniques to grower-standard weed management programs in each system, including both no-till and full-till standard treatments in the conventional system. Italian ryegrass populations were monitored, and wheat yield was measured both before and after HWSC application. In both organic and conventional cropping systems, HWSC treatments did not provide better Italian ryegrass control than the grower-standard treatments. The conventional program including tillage boosted Italian ryegrass populations. These results suggest that HWSC treatments did not enhance Italian ryegrass control compared to grower-standard practices in either the organic or conventional systems. Additionally, broadleaf weeds may retain enough seeds to be viable targets for HWSC. Incorporating best practices, such as a timely crop harvest, is key for understanding and optimizing HWSC. / Master of Science / Harvest weed seed controls (HWSC) destroy weed seeds that the weed plant retains at the time of crop harvest. On a typical farm, these weed seeds pass through the crop harvester and get spread across the field along with other plant materials. HWSC directly targets weed seeds, differentiating itself from normal weed management practices, such as herbicides, that kill emerging or emerged weed plants. With HWSC, weed seeds never enter the soil seed bank, thus depleting weed populations over time. HWSC works through mechanical means, such as crushing, burning, or removal. For conventional farmers battling herbicide resistant weeds, HWSC can provide effective weed management by diversifying weed management programs. HWSC also has promise as a new chemical-free weed management for organic farmers. HWSC relies on crops and weeds having coincidental maturity; seeds released from the plant (shattered) before crop harvest cannot be targeted by HWSC. An experiment was designed to collect weed seeds weekly as they shatter throughout the growing season, continuing until three weeks after the ideal date to harvest crops, thereby simulating a situation where weather or logistical factors prevented a timely crop harvest. This experiment monitored four broadleaf species and two grass species that infest soybean fields. Broadleaf species shattered seeds at increasing rates throughout the soybean growing season, with each species shattering over 50% of captured seed during the simulated harvest delay. Compared to broadleaf weeds, grass species shattered relatively more seed early in the growing season. This experiment indicates that broadleaf weeds may be more suited to control by HWSC. HWSC was also used in organic and conventional winter wheat fields infested with Italian ryegrass. These experiments compared two HWSC techniques, windrow burning of field residue and residue removal to standard weed management programs in each system. Windrow burning incinerates field residues, eliminating weed seeds within. Residue removal takes all field residues off the field for disposal elsewhere. While the standard organic weed management program involved tillage by default, the conventional cropping system featured both no-till and full-till standard weed management programs. Italian ryegrass populations were monitored through population counts, biomass collections, and counting of seed remaining at harvest. Wheat yield was also recorded. These measurements were taken both before HWSC application and after the first year of HWSC, to compare year-to-year changes. In the organic cropping system, Italian ryegrass populations grew and wheat yield decreased at similar rates for both HWSC treatments and the standard weed management program. In the conventional cropping system, Italian ryegrass populations declined and wheat yield increased for HWSC and the no-till standard treatments. Tillage, however, boosted Italian ryegrass populations, keeping them at similar levels to the previous growing season. These results suggest that HWSC treatments did not enhance Italian ryegrass control compared to standard practices in either the organic or no-till conventional systems. Though these results indicate that broadleaf weeds may retain enough seeds to be viable targets for HWSC, more research is needed to optimize HWSC for Italian ryegrass control, especially for organic growers. Incorporating best agricultural practices, such as a timely crop harvest, is key for improving HWSC’s efficacy. Commercial implementation of HWSC depends on further understanding of how specific HWSC practices, such as windrow burning, interact with the agricultural landscape, including effects on landscape aesthetics and soil nutrition. HWSC holds promise for diversifying weed management and limiting reliance on herbicides, but its true potential is yet to be revealed.

Russian knapweed (Acroptilon repens) is an invasive perennial forb that has become well established in much of the western United States and Canada since the late 1800s. Aminopyralid is a relatively new pyridine carboxylic acid herbicide registered for use on rangelands and has provided excellent control of Russian knapweed in many studies. Research trials were conducted on two adjacent plot sites at Dinosaur National Monument to evaluate the effects of a single spring goat grazing paired with a fall application of aminopyralid at 0, 53, 70, 88, and 105 g ae ha-1 on Russian knapweed control. Russian knapweed density, canopy cover, and biomass were reduced to 0 or near 0 by all rates of aminopyralid, regardless of grazing treatment. Conversely, desirable grass cover and biomass increased at all rates of aminopyralid regardless of grazing treatment. Aminopyralid provided excellent control of Russian knapweed at all rates tested. Desirable perennial grass species have the potential to be injured when growth regulator herbicides are used for broadleaf weed control. Greenhouse trials performed at Utah State University and field trials performed in Logan, UT from 2009&ndash2011 evaluated tolerance and response of six native perennial bunchgrasses to growth regulator herbicides. Grasses used in the study included tall wheatgrass, bluebunch wheatgrass, Great Basin wildrye, Indian ricegrass, big bluegrass, and bottlebrush squirreltail. Two rates each of aminopyralid, aminocyclopyrachlor, and clopyralid were evaluated. Herbicide test rates were based on the labeled rate for control of Russian knapweed and other creeping perennials. Tolerance to herbicides varied among grass species. Petri&ndashdish trials showed reductions in root length by all three herbicides in all six speceis 14 days after treatment (DAT). Shoot length was significantly reduced by both rates of aminopyralid (123 and 246 g ae ha-1) and 280 g ai ha-1 of amincyclopyrachlor. The same species were evaluated in the field and greenhouse in response to postemergence applications of the same herbicides. Of the six grass species tested, &lsquoSherman&rsquo big bluegrass appeared to be highly tolerant to aminopyralid, clopyralid, and aminocyclopyrachlor, and &lsquoMagnar&rsquo Great Basin wildrye and Anatone bluebunch wheatgrass appeared to be the most sensitive to aminopyralid and aminocyclopoyrachlor in both the field and the greenhouse.

Abstract Ecological based weed management strategies are imperative in cropping systems when herbicide use is limited or prohibited. Herbicides are not applicable in controlling wild oat (Avena fatua L.) in oat (Avena sativa L.) cropping systems, as they are closely related. Moreover, herbicide use is prohibited in organic oat cultivation, resulting in a need for developing alternative weed management strategies. Enhancing the crop competitive ability (CA) can be an essential strategy in managing weeds in such instances. Two studies were carried with the objectives to: 1) evaluate newly developed oat genotypes for their CA against wild oat; and 2) develop a competitive organic oat cropping system integrating mechanical and cultural weed control practices. In the first study, seven oat lines deliberately bred for enhanced CA and their two parental cultivars were evaluated for the CA with wild oat. The genotypes yielded similarly in the presence and in the absence of wild oat competition. The tall oat line SA050479 with greater seedling leaf size was more wild oat suppressive among all lines. Moreover, SA050479 had greater yield potential and grain quality; thus, it has the potential to be developed as a commercial wild oat suppressive cultivar. The second study used two contrasting levels of genotype, row spacing, crop density and a post-emergence harrowing and a non-harrowed control in two organic oat fields to develop an integrated weed management system. High crop density and harrowing increased the grain yield by 11% and 13% respectively. The competitive cultivar CDC Baler and high crop density (500 plants m-2) reduced weed biomass by 22% and 52% respectively. Harrowing reduced weed density by more than 50% in three site-years. The cultural and mechanical weed control practices when combined were additive in increasing grain yield and reducing weed biomass. Oat seed yields were increased by 25% when high crop density planting and harrowing were combined. Similarly, the combined effect of competitive cultivar, high crop density, and post-emergence harrowing were greater as weed biomass was reduced by 71%. The outcome of this project implies the importance of enhancing the crop CA by means of crop breeding and integrating cultural and mechanical weed control strategies. Furthermore, this study was able to identify the importance of ecological based weed management strategies in order to overcome the constraints in weed management in present oat cropping systems.

Abstract Ecological based weed management strategies are imperative in cropping systems when herbicide use is limited or prohibited. Herbicides are not applicable in controlling wild oat (Avena fatua L.) in oat (Avena sativa L.) cropping systems, as they are closely related. Moreover, herbicide use is prohibited in organic oat cultivation, resulting in a need for developing alternative weed management strategies. Enhancing the crop competitive ability (CA) can be an essential strategy in managing weeds in such instances. Two studies were carried with the objectives to: 1) evaluate newly developed oat genotypes for their CA against wild oat; and 2) develop a competitive organic oat cropping system integrating mechanical and cultural weed control practices. In the first study, seven oat lines deliberately bred for enhanced CA and their two parental cultivars were evaluated for the CA with wild oat. The genotypes yielded similarly in the presence and in the absence of wild oat competition. The tall oat line SA050479 with greater seedling leaf size was more wild oat suppressive among all lines. Moreover, SA050479 had greater yield potential and grain quality; thus, it has the potential to be developed as a commercial wild oat suppressive cultivar. The second study used two contrasting levels of genotype, row spacing, crop density and a post-emergence harrowing and a non-harrowed control in two organic oat fields to develop an integrated weed management system. High crop density and harrowing increased the grain yield by 11% and 13% respectively. The competitive cultivar CDC Baler and high crop density (500 plants m-2) reduced weed biomass by 22% and 52% respectively. Harrowing reduced weed density by more than 50% in three site-years. The cultural and mechanical weed control practices when combined were additive in increasing grain yield and reducing weed biomass. Oat seed yields were increased by 25% when high crop density planting and harrowing were combined. Similarly, the combined effect of competitive cultivar, high crop density, and post-emergence harrowing were greater as weed biomass was reduced by 71%. The outcome of this project implies the importance of enhancing the crop CA by means of crop breeding and integrating cultural and mechanical weed control strategies. Furthermore, this study was able to identify the importance of ecological based weed management strategies in order to overcome the constraints in weed management in present oat cropping systems.

Field pea (Pisum sativum L.) is an important grain legume in western Canada. Growers can, however, be reluctant to include pulse crops such as field pea in their rotation because they are poor competitors with weeds. This thesis research was conducted to determine whether competitive differences exist among semi-leafless field pea cultivars and to determine the mechanism(s) driving competitive differences. Cultivars included in the studies were chosen on the basis of varying seed size and vine length, which are traits known to confer competitive ability. Differences in competitive ability were identified among cultivars as yield loss ranged from 9% to 31% and 14% to 31% for model weed seed return. However, cultivars were inconsistent in their competitive ranking as cultivars typically performed well for one metric, but not both. None of the traits measured in this study correlated with competitive ability. The greenhouse research was unable to identify the mechanism responsible for these competitive differences. Focal pea plants generally responded to the presence of below-ground neighbours by allocating more resources to shoot production. Therefore, semi-leafless field pea cultivars exhibit differences in below-ground responses to neighbours and it may be useful to include this as part of the selection criteria in breeding programs.

No description available.

Integrating cultural weed management practices with herbicides is an important strategy to reduce wild oat (Avena fatua L.) populations in Alberta, Canada. The purpose of this thesis is to expand the knowledge on wild oat seed banks and seedling emergence within integrated weed management systems. Field experiments were conducted from 2006-2007 to examine the impact of crop rotation, barley cultivar, barley seeding rate and herbicide rate on wild oat seed bank density, seed mortality, seedling emergence and seedling survivorship. Management systems consisting of diverse crop rotations, tall barley cultivars and increased barley seeding rates reduced wild oat seed bank density, seedling emergence and seedling survivorship, especially at low herbicide rates. Wild oat seed banks predicted subsequent wild oat emergence, whereas biomass and emergence strongly predicted seed banks. Lastly, 50% wild oat emergence was achieved at 537 and 509 growing degree days in 2006 and 2007, respectively, in Lacombe, Alberta. / Plant Science

Russian knapweed (Acroptilon repens) is an invasive perennial forb that has become well established in much of the western United States and Canada since the late 1800s. Aminopyralid is a relatively new pyridine carboxylic acid herbicide registered for use on rangelands and has provided excellent control of Russian knapweed in many studies. Research trials were conducted on two adjacent plot sites at Dinosaur National Monument to evaluate the effects of a single spring goat grazing paired with a fall application of aminopyralid at 0, 53, 70, 88, and 105 g ae ha-1 on Russian knapweed control. Russian knapweed density, canopy cover, and biomass were reduced to 0 or near 0 by all rates of aminopyralid, regardless of grazing treatment. Conversely, desirable grass cover and biomass increased at all rates of aminopyralid regardless of grazing treatment. Aminopyralid provided excellent control of Russian knapweed at all rates tested. Desirable perennial grass species have the potential to be injured when growth regulator herbicides are used for broadleaf weed control. Greenhouse trials performed at Utah State University and field trials performed in Logan, UT from 2009&ndash2011 evaluated tolerance and response of six native perennial bunchgrasses to growth regulator herbicides. Grasses used in the study included tall wheatgrass, bluebunch wheatgrass, Great Basin wildrye, Indian ricegrass, big bluegrass, and bottlebrush squirreltail. Two rates each of aminopyralid, aminocyclopyrachlor, and clopyralid were evaluated. Herbicide test rates were based on the labeled rate for control of Russian knapweed and other creeping perennials. Tolerance to herbicides varied among grass species. Petri&ndashdish trials showed reductions in root length by all three herbicides in all six speceis 14 days after treatment (DAT). Shoot length was significantly reduced by both rates of aminopyralid (123 and 246 g ae ha-1) and 280 g ai ha-1 of amincyclopyrachlor. The same species were evaluated in the field and greenhouse in response to postemergence applications of the same herbicides. Of the six grass species tested, &lsquoSherman&rsquo big bluegrass appeared to be highly tolerant to aminopyralid, clopyralid, and aminocyclopyrachlor, and &lsquoMagnar&rsquo Great Basin wildrye and Anatone bluebunch wheatgrass appeared to be the most sensitive to aminopyralid and aminocyclopoyrachlor in both the field and the greenhouse.