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Weed Control Strategies for North Dakota and the Northern Great Plains


Objective 1: Investigate new herbicides in minor crops to fill existing weed control gaps. Although minor crop acreage has increased over the past decade, the process for herbicide registration in minor crops moves very slowly and has not filled weed control gaps that exist across the northern plains. Crop protection product manufacturers base their registration priorities on crops with the largest number of acres. Many North Dakota crops do not fall into the major crop category, so registration of herbicides for these crops is much lower on the priority list. Research is needed to document that a product is safe on a given crop and that it can provide better weed control than currently labeled herbicides. Some new active ingredients have become available in recent years. These materials are available for universities to conduct research to determine how they may fit production practices in minor crops. The specific agronomic and economic strengths and weaknesses of each product need to be identified. This research can lead to herbicide registrations in minor crops to help growers control problem weeds. <P>Objective 2: Determine the effectiveness of fall-applied herbicides for winter annual and summer annual weed control. A shift to winter annual weeds has been observed in recent years. Winter annual weeds have increased because more farmers are using no-till systems as well as growing more minor broadleaf crops where effective herbicides are not available. Tank mixing a soil residual herbicide with glyphosate in the fall may provide better control of winter annuals and give growers application flexibility. Removing fall emerging weeds would result in fewer weeds to control in the spring, likely increasing the effectiveness of the spring burndown. Effective fall weed control would also preserve precious water resources and would allow soils to warm up faster in the spring.<P> Objective 3: Determine if pulse crop cultivars differ in their sensitivity to PPO-inhibitors. Dry pea, lentil, and chickpea production are hampered by the lack of herbicides to control weeds. North Dakota farmers have listed weeds as their number one problem and top research priority. Three herbicides that can now be used for certain pulse crops include sulfentrazone, flumioxazin, and saflufenacil. Each herbicide differs slightly in spectrum of weeds controlled. Some crop injury has been observed in certain soils and environmental conditions. Pulse growers have questioned whether pulses differ (green vs. yellow pea, green vs. red lentil, kabuli vs. desi chickpea, etc.) in their sensitivity to these herbicides. Differential tolerance among soybean and dry bean cultivars has been reported for sulfentrazone and flumioxazin. Given this evidence of differential sensitivity, it is possible that pulse crop cultivars also may respond differently to these herbicides. This project will evaluate pulse crop cultivar sensitivity to PPO inhibitors through field and laboratory studies.

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Non-Technical Summary: Weeds generally are considered one of the greatest problems in crop production. Changes in weed species, weed densities, and weed resistance to herbicides have made weed control more challenging. These changes are especially important for crops that do not compete well with weeds such as lentil, chickpea, and flax. About 85 percent of all pesticides used in North Dakota are herbicides. However, the major herbicide manufacturers focus most of their resources on major crops such as corn, soybean, and wheat. Minor crops in North Dakota such as canola, safflower, dry pea, lentil, chickpea, and flax receive much less attention and thus have few registered herbicides. The State of North Dakota has appropriated money to fund research that will lead to new product registrations in minor crops. Herbicide efficacy and crop tolerance data gathered by this project will help register new weed control products. New herbicide registrations will provide growers with more choices to solve weed control issues in minor crops. Many ND growers have adopted variations of direct seeding or no-till. As growers moved away from tillage, winter annual weeds that typically were controlled by tillage now need to be controlled through the use of herbicides or cultural methods. This research may provide growers with options to control winter annual weeds more effectively through fall applications. This will lead to cleaner fields in the spring and ultimately higher yields, crop quality, and profitability. Dry pea, lentil, and chickpea acres have increased significantly over the past decade. However, grower surveys still say that weed control remains their top priority. Growers want herbicide options that control weeds effectively without causing crop injury. The most effective herbicides we currently have or will have in the near future are influenced by soil and environmental conditions. It is important to understand these conditions to maximize weed control and crop safety. The objectives of this project will address ways to maximize weed control through fall and spring applications as well as determining crop sensitivity to commonly used herbicides. <P> Approach: Objective 1: Investigate new herbicides in minor crops to fill existing weed control gaps. We will conduct field studies to optimize herbicide use patterns (timing, rate, adjuvant) for controlling weeds in minor crops such as pea, lentil, chickpea, canola, flax, dry bean, safflower, and sunflower. A standard experiment will consist of 3 by 9 m plots arranged in a randomized complete block design with three or four replications. All data will be subjected to analysis of variance. Treatments will be applied with either a tractor-mounted or bicycle sprayer. If a new product is found to be safe on a specific crop and adequately controls a problem weed, we will consult with commodity groups to determine if registration should be pursued. Products that exhibit good safety will be submitted to IR-4 for residue studies and development of tolerance petitions. Objective 2: Determine the effectiveness of fall-applied herbicides for winter annual and summer annual weed control. We will conduct field studies that target problem winter and summer annual weeds. Fall and spring applications of various soil residual herbicides will be evaluated. These studies will be conducted over multiple years to verify consistency of results. A standard experiment will consist of 3 by 9 m plots arranged in a randomized complete block design with three or four replications. Objective 3: Determine if pulse crop cultivars differ in their sensitivity to PPO-inhibitors. Field and laboratory studies will be conducted to determine if pulse crop cultivars respond differently to PPO inhibitors sulfentrazone, flumioxazin, and saflufenacil. At least two cultivars from different market classes will be selected for dry pea, lentil, and chickpea. The field experiment statistical design will be a split plot arrangement in a randomized complete block design with four replications. Cultivar will be the whole plot and herbicide concentration the sub-plot. Each treatment will be evaluated visually for crop tolerance and crop height will be measured twice during the season. Crop yield and test weight will be determined following harvest with a small-plot combine. In the laboratory, seeds will be surface-sterilized in a 5 percent sodium hypochlorite solution, rinsed, and dried at room temperature. Seeds will be imbibed in distilled water spiked with herbicide at various concentrations. Four imbibed seeds will be transferred to the upper trough of individual seed germination pouches that contain 40 ml of the appropriate herbicide solution in the lower reservoir of the pouch. Soil potting mix will be placed over the top of the seeds to simulate soils conditions and prevent seeds from drying out. The pouches will be placed in the darkened growth chamber for four days after which hypocotyls and root lengths will be measured. Variables will include cultivar and herbicide concentration. The study will be a completely randomized design with four replications, and the study will be conducted two times. All data will be subjected to analysis of variance.

Jenks, Brian
North Dakota State University
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