Clomazone is a carotenoid biosynthesis inhibitor commonly used as a preemergence and postemergence herbicide in rice for the control of grass weeds. Rice injury can occur and symptoms are often associated with soil characteristics and environmental conditions. The objective of this research was to investigate how environmental conditions and planting density influence clomazone injury in rice plants. Also, different fertility treatments were assessed to determine if remediation from clomazone injury occurred. Field studies were conducted in 2008 and 2009 to determine the role of planting date, planting density and soil characteristics on clomazone injury in rice plants. Also, another field study was conducted in 2010 to assess any clomazone injury remediation benefits selected fertility treatments might have in rice cropping systems. In the 2008 and 2009 field studies, hybrid rice was seeded at three densities that comprised a range of slightly lower, slightly higher and commonly recommended planting rates. Two planting dates, March and April, were a test parameter to simulate early and optimal planting dates. Two locations with different soil characteristics, near Eagle Lake and Beaumont, TX, were the study sites. Clomazone herbicide treatments were applied at different rates and timings following planting. Visual injury ratings and yield data were collected during this two-year, two location study. Clomazone injury in rice was more severe in the coarse-textured soils planted at the early, March planting date near Eagle Lake. Visual injury ratings as high as 90% were observed in some plots. Injury was less severe in the April planting date near Eagle Lake, and at both planting timings near Beaumont. In both locations, clomazone injury did not translate into yield loss at any seeding rate or planting timing. In 2010, field studies were conducted near Eagle Lake and Ganado, TX to assess fertility-based clomazone injury remediation. In one experiment, hybrid rice plots were subject to linearly increasing rates of clomazone herbicide to produce a standard curve of clomazone injury. In the second experiment, a uniform, label rate of clomazone was applied to induce injury for the assessment of the effect of fertility amendments on clomazone-injured rice. Fertility treatments consisted of nitrogen-based fertilizers and foliar-applied iron sulfate and magnesium sulfate. Visual injury ratings, plant height, and yield were collected during the study. Also, tissue samples were collected three times for laboratory analysis of chlorophyll content. In the standard curve experiment, herbicide injury increased with increasingly higher rates of clomazone applied. The highest visual injury was observed in plots receiving the highest rates of clomazone. In the remediation experiment, fertility treatments had a significant effect in only one tissue-sampling event at Eagle Lake as determined by laboratory analysis for chlorophyll content. Fertility amendments did not have a significant effect on visual injury ratings at either location at any assessment event. Specific fertility treatments significantly increased plant height in three measurement events, and yield at the Ganado locations. Plots receiving treatments containing nitrogen fertilizers produced taller plants at both locations, and increased yield at the Ganado location.

Lack of technical knowledge and proper soybean cultivars are barriers for organic farmers to take advantage of increased organic soybean demand in Manitoba from domestic and international markets. The objective of the present study was to evaluate the performance of 12 early season non-GM food grade soybean cultivars under organic management in southern Manitoba. Cultivars were seeded on four organic farms and one transition to organic farm in southern Manitoba in 2014 and 2015. The mean cultivar yield ranged from 1384 to 1807 kg ha-1, with a mean of 1536 kg ha-1. Cultivars ‘Savanna’ and ‘Toma’ were high performers, but exhibited low stability across sites. Partial Least Squares Regression Analysis indicated that soybean mature height, and biomass at R5 positively contributed to final grain yield. Early height positively contributed to biomass at R5 but negatively affected final grain yield. Soil nitrate content negatively contributed to final grain yield. Weed competitiveness was of particular interest in this study. Contrary to previous reports, cultivars that exhibited early season vigour often resulted in lower yields, biomass accumulation, and increased weed presence as compared to other cultivars. / October 2016

Giant reed (Arundo donax L.) is a candidate to provide feedstock for the Portland General Electric power plant in Boardman, Oregon. Giant reed is a fast perennial grass, producing 23-27 metric tons ha⁻¹ of biomass and has the ability to adapt to diverse environments making it a good candidate for biomass production. This study tested postemergence and preemergence herbicides for controlling weeds in giant reed during the establishment year in which giant reed plants are more sensitive to weed competition. The greenhouse study demonstrated that among the tested herbicides, bromoxynil plus MCPA at 0.841 kg ai ha⁻¹, nicosulforun at 0.035 kg ha⁻¹, and dimethenamid-p at 0.735 kg ha⁻¹ did not injure giant reed. In a field study, preemergence application of dimethenamid-p at 0.735 kg ha⁻¹ followed by a postemergence application of 2,4-D amine at 0.560 kg ha⁻¹ and a postemergence application of bromoxynil plus MCPA at 0.841 kg ha⁻¹ did not injure giant reed. The presence of weeds in a field does not always mean that crop yield will be reduced and there are some periods during the growing season when weeds will not cause considerable yield loss. Therefore, predicting a critical period of weed control (CPWC) that includes the best time for weed control in giant reed could improve weed management in the field. The length of the CPWC could be different depending on the level of acceptable yield loss (AYL). Our results are reported for AYL of 5 and 10%. The CPWC started at 290 accumulated growing degree days (GDD) and ended at 820 for a 5% AYL, while for a 10% AYL, it started at 333 GDD and ended at 727 GDD. Based on the results, there are some herbicides which could be selected for further study for weed control in the giant reed and the estimated CPWC which could be used to inform weed management practices in giant reed production. / Graduation date: 2013

There is little information published on red sorrel (Rumex acetosella L.), a perennial weed that is considered a serious problem in wild blueberry production. Hexazinone, a photosystem II inhibitor, has been used in wild blueberry fields for more than 30 years. Hexazinone efficacy on red sorrel has declined over time. Therefore, a two year study was conducted to examine hexazinone alternatives that can be sprayed in wild blueberry fields. Red sorrel ramets from mature blueberry fields were tested to determine whether long-term spraying of hexazinone selected for resistant red sorrel. The results show that hexazinone+rimsulfuron/nicosulfuron may be a alternative for hexazinone. Red sorrel from some blueberry fields is hexazinone-resistant and the resistance is caused by a Phe255 to Val mutation in the psbA gene.

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.

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

Cover crops not only improve soil conditions, but can also suppress weed growth. In a field experiment the influence of two cover crops, Secale cereale (stooling rye), and Lolium multiflorum (annual ryegrass), on the growth of Zea mays (maize) and C. esculentus (yellow nutsedge) was compared to the latter crop and weed’s growth at three control treatments which involved weed residues left on the soil surface, application of herbicides and weed control by hoeing. Maize emergence and growth were delayed in the presence of residues of both cover crop species, especially in annual ryegrass residues. C. esculentus growth was significantly inhibited in the area between the maize planting rows by the cover crops for the first 14 days after maize emergence, but this growth suppressing effect diminished after 28 days. In a controlled environment study, the influence of the same cover crops, together with Avena sativa (oats) and three cultivars of annual ryegrass were evaluated. Maize and C. esculentus growth were suppressed, especially by the root residues of the cover crops with the annual ryegrass cultivar ‘Midmar’ being the most suppressive. Chemical analysis of the leachate of root residues indicated the presence of phenolic acids and benzoxazolin-2(3 H)-one (BOA). It is suggested that weed growth could be reduced by the allelochemicals leached from cover crop residues but in order to achieve prolonged, effective weed control the combination of mulch retained on the soil surface and the application of herbicides will required. In an integrated weed management approach a possible reduction in the type and number of herbicide applications required for effective weed control, could be implemented. / Thesis (PhD)--University of Pretoria, 2012. / Plant Production and Soil Science / unrestricted

Early planting soybean (Glycine max L.) strategies across the mid-southern United States has complicated weed management in the form of post-harvest weed control. Research has investigated the use of cover crops to aid in management of weed populations during winter months, but conventional cover crops provides minimal weed management benefit immediately following cash crop harvest. Inter-seeding cover crop into crop canopies has potential to promote earlier cover crop establishment, thus creating higher potential for post-harvest weed management. However, factors such as inter-seeding timing, herbicide residue, as well as harvest aid applications must be considered. Therefore, studies were conducted in Mississippi in 2017, 2018, and 2019 to determine if cover crops inter-seeded through soybean could improve weed control used in conjunction with common management strategies in Mississippi production systems. Conclusions drawn from these studies indicate inter-seeded cover crops can be utilized in soybean production systems to improve weed management after harvest.

Weed control is the primary challenge in organic dry edible bean (Phaseolus vulgaris L.) production, however no previous Canadian studies have considered cereal cover crops for organic pulse production. The objectives of this study were to characterize the effects of fall rye (Secale cereal L.), barley (Hordeum vulgare L.) and oat (Avena sativa L.) cover crops and tillage management on weeds and the soil microclimate in organic dry beans. Above ground weed biomass was significantly lower in fall rye (3778 kg ha -1) and NT treatments (4867 kg ha -1). Fall rye significantly lowered spring soil nitrate-N by 72% and 74% in 2011 and 2012, respectively. Cover crops did not affect soil moisture or soil growing degree day (GDDsoil ) accumulation in early spring. Further research is needed on fall-seeded fall rye termination in organic conditions to reduce its competitiveness with the main crop. / October 2015

Weeds are considered a major problem for organic wild blueberry (Vaccinium angustifolium Ait.) production due to their excessive growth and limited management options available. Therefore, the primary objective of this study was to investigate burning in combination with sulphur application as a weed management option for organic blueberry production. In addition, Finalsan® and EcoclearTM as potential candidates for perennial weed control in organic production were evaluated. Burned and sulphur plots produced higher blueberry stem density, blueberry cover and yield compared to mowed and no-sulphur plots, respectively, although, the interaction was not significant. Similarly, low weed density and cover were observed in burning and sulphur application plots. Mycorrhizal colonization in blueberry roots was significantly higher in burned plots than mowed plots. A single application of Finalsan® and EcoclearTM effectively controlled goldenrod, sweet fern and bracken fern. However, a single application of either product did not control wild raisin or moss.