Many pathogens can cause diseases in dry edible beans. Diseases can reduce yield and quality, and add to production costs. Disease management tools and strategies are available and can reduce the potential impact of diseases.
This section describes the general principles of disease management, followed by a discussion of the most problematic diseases in the North Dakota and Minnesota production regions. Photographs at the end of this publication provide examples to identify common diseases in dry edible beans.
1. Assess your greatest threats
While many diseases impact dry edible beans, each disease is not a threat every year and in every location. Try to determine which diseases are more likely to cause you problems. Proactive management of the most likely disease threats in each field may reduce the chances of yield and quality losses due to disease.
Field history: If you consistently have problems with a specific disease on a specific field (for example, root rots) or have had a recent outbreak of a disease on your farm (for example, anthracnose or white mold), put greater emphasis on managing that disease when preparing for the season (for example, plant a cultivar resistant to that specific disease of concern or budget for a fungicide application).
Environment: Although climatic trends exist, nobody can predict the weather accurately and consistently in an upcoming growing season. However, assessing your local environmental conditions, and responding appropriately to them, is very important.
For example, if rain and cool temperatures are forecast as your beans begin to flower, a foliar fungicide for white mold may be very important. If heavy dews and fog occur frequently, you should look for rust and prepare to respond with a fungicide if it is found.
Adapt: Every year is different, and the greatest disease threats can change quickly. For example, frequent thunderstorms may create conditions favorable for bacterial blight outbreaks, even if the month before had been hot and dry.
2. Keep pathogens and beans separated
Certified disease-free seed: Certified seed must meet certain quality standards concerning seed-borne pathogens. You have no guarantee that the seed is pathogen-free; however, planting certified seed is the best way to minimize the introduction of bean pathogens to the seed. This is particularly important for the pathogens that cause bacterial blights and anthracnose.
Crop rotation and geographic separation: A rotation of three or four years out of beans is recommended, and longer rotations may be beneficial in some cases. Avoid planting next to last year’s bean field, especially if disease pressure was severe. Some pathogens overwinter and can be blown in the wind to adjacent fields the following season.
Avoid cultivating or moving through a field when plants are wet: This helps prevent the spread of pathogens, especially those that cause bacterial blights and anthracnose.
3. Identify the disease or pathogen
Active scouting and correct identification of diseases in the field are critical to mitigating outbreaks. This is true not only in the current growing season but in future growing seasons in that field as well.
Scout: You have no substitute for proper scouting (walking the fields). Many diseases are not seen unless you are examining leaves actively by hand
Identify: Take advantage of many knowledgeable Extension agents, crop consultants, or seed company agronomists.
As an example of the importance of proper identification, if you misidentify halo blight (a bacterial disease) as rust (a fungal pathogen) and select a fungicide to manage rust, you will not manage halo blight and will add significant production costs needlessly.
4. Strengthen the bean plant
Plant disease-resistant cultivars: Genetic resistance is a cost-effective way to manage diseases.
Manage fertility: Provide adequate soil fertility (based on soil test results) and adequate trace minerals such as zinc.
Avoid excess nitrogen levels that stimulate lush plant growth, which can enlarge the canopy and provide a microclimate conducive to disease development.
Control weeds: Weeds can be hosts to pathogens that cause diseases in the dry beans.
Control volunteers: Volunteer bean plants often harbor pathogens, which limits the effectiveness of your rotation to reduce inoculum and may facilitate pathogen race changes (for example, rust).
5. Attack the pathogen
Scout fields for disease: For many diseases, early detection is critical for effective management.
Foliar fungicide selection: Fungicides may aid in disease management by limiting new infections; however, fungicides are not equally effective on all pathogens. For example, some fungicides are effective on rust but have minimal efficacy on white mold, and vice versa. Match the more effective fungicide with your target disease.
Foliar fungicide timing: The timing of an application is critical and different for every disease. For example, an application to manage white mold should occur at the beginning of flowering (R1), while an application to manage rust should occur shortly after pustules are first identified. An application later than these two recommended times greatly reduces the efficacy of the application and increases the likelihood of a disease epidemic.
Seed treatments: Fungicide seed treatments may limit damping-off and root rots and aid the establishment of a robust stand. The use of seed treatments is particularly important in fields with a long history of bean production.
6. Stay engaged and adapt
Disease prevalence, pathogen races, management tools, and information strategies change constantly. Staying engaged will help you manage the most critical diseases with the most current and effective tools.
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