Dry Bean – Diseases
Research underway with Dr. Syama Chatterton, a Plant Pathologist with Agriculture and Agri-Food Canada is looking at spore trapping to help predict disease risk in bean fields. Please see the one page research summary document “Better Tools in Sight for Dry Bean Disease Management“.
Dry beans are very susceptible to a number of diseases and few chemical control measures are available – it’s important to use an integrated management program in dry bean production. Disease prevention recommendations include:
- Crop Rotation– Follow a diverse rotation with at least four years between dry bean crops which can reduce pathogen loads in the soil. There may be no safe rotation length for some diseases. Avoid planting adjacent to last year’s bean field because many diseases are wind-borne and very mobile (shorter rotations are acceptable as long as diseases are not a problem).
- Field Preparation: Plow residue into the soil to avoid it scattering. Burying it will reduce survival of the pathogens, but take care to avoid erosion issues.
- Seed Source and Handling – Plant clean seed that is disease free, in particular, avoid seed with Bacterial Blight. Planting certified seed produced in arid regions is an effective technique for controlling Bacterial Blight. Seed should be handled gently both in storage and seeding operations to avoid damage to the seed coat. Mechanically damaged seed is prone to fungal diseases during germination, and young seedlings are less vigorous and more susceptible to fungal diseases – Baldhead is also a symptom of mechanically damaged seed.
- Seed Treatments – Seed treatments will help protect seeds and seedlings from seed-borne and soil-borne pathogens and help ensure good establishment of a strong, vigorous crop.
- Variety Selection – Resistance to Common Blight and White Mould is minimal. However, growth habit can affect how wet the canopy stays, greatly influencing the development of diseases like White Mould. Choosing varieties that are more upright may result in a drier canopy with less disease.
- Weed Control – Keep the crop weed free, which will help reduce canopy cover and provide a drier canopy. Some weeds can host pathogens, increasing disease pressure.
- Proper Fertilization – Balanced nutrition is important to avoid nutrient deficiencies that may stress the plant and make it more susceptible to disease. In particular, zinc deficiencies can result in more disease concerns. Over application of nitrogen can also increase disease risk, as a lusher canopy can create a favourable environment for disease.
- Row Spacing and Tillage – Wider row spacing in row crops, compared to solid seeding systems, will have more airflow through the canopy, reducing disease pressure. If soil is compacted and hard, root diseases can be more problematic. Tillage near bean rows to break soil up and allow improved root growth can reduce the severity of root diseases.
Scouting Your Field for Diseases
Scouting is one of the most powerful practices to effectively manage crops. It allows early detection of disease symptoms, provides opportunity for mitigation of spread and minimizes the impact on yield.
- Develop a systematic approach beginning soon after crop emergence.
- ALWAYS bring along a shovel to dig up plants. Pulling plants will not work when assessing root and nodule health.
- Scout weekly beginning after the crop emerges until maturity, first looking at plant stand, then root/seedling diseases, and as the crop develops for foliar diseases.
- Take photos, mark problem areas in the field, collect whole plants (leaves, stems and roots) for identification of the disease (put in plastic Ziploc, label with date and location and keep cool until sent to lab).
- Check in a ‘W’ shaped pattern in the field stopping at 5-10 locations,
- Take note of yellowing patches, and problem areas in the field, these are often the source of disease spread and if recurring problems are noted these areas may benefit from a separate management strategy.
Keeping crops healthy and disease free is a priority for producers and one practice that can help achieve these goals is applying fungicide. Producers need to consider both disease risk and economics when deciding whether to apply a fungicide.
Disease risk is influenced by the field history (crop rotation, levels of disease in previous susceptible crops; the environmental conditions such as temperature and precipitation levels that may favour disease development; and the level of variety resistance to the disease. A fungicide should only be applied if the risk of disease is high and an economic return is expected.
Once a decision has been made to apply fungicide, the two most important considerations are timing and coverage. Plant growth and disease progress can be very rapid so it’s essential to be ready to apply the fungicide when it’s needed. Missing the ideal window is very costly and a fungicide applied at the wrong time can lose much of its effectiveness
Good coverage is also critical for a fungicide to be effective. To achieve this, target the plant part that needs protection, be it the leaves, stems, or leafstalks, and do so with adequate droplet density. This is because most fungicides do not move from one part of the plant to another very well. That is why it is important to understand the disease, including which plant parts must be covered by spray and where – top, middle, or bottom – they are in the canopy. Then assess how easy it will be for a spray to reach the target zone.
Determine if more than one application should be done by scouting. If applying more than one application, make sure to rotate fungicide groups and do not use a single mode of action more than once. Consult the product’s label. (Forsythe, Trudy K. “Timing and Coverage are Important Factors in Fungicide Application”)
Management of Fungicide Resistance
Just as with different herbicide groups, fungicide groups also have the potential to develop resistance in the disease population. Any fungal pathogen population may contain some strains naturally insensitive to various fungicides. A gradual or total loss of disease control may occur if these fungicides are used repeatedly in the same fields. Other resistance mechanisms that are not linked to site of action, but are specific for individual chemicals, such as enhanced metabolism, may also exist.
To delay fungicide resistance/insensitivity
- Use a fungicide rotation – rotate the use of fungicides with others from different groups that control the same pathogens.
- Tank mix fungicides that have a higher risk of developing insensitivity with other fungicides from a different group.
- Do not apply more than the maximum number of applications listed on the label. Avoid consecutive sprays of the same fungicide, or other fungicides in the same group, in a season.
- Fungicide use should be based on an integrated pest management (IPM) program that includes scouting and accurate record keeping of fungicide use and crop rotation. An IPM program also considers cultural, biological, and other chemical control.
- Monitor treated fungal populations for signs of fungicide insensitivity. If disease continues to progress after treatment, do not reapply the same product with a higher rate.
- If you observe fungicide insensitivity, discontinue use of the product and switch to a fungicide with a different mode of action.
- Contact your local regional crop specialist or certified crop advisor for any additional pesticide management and/or IPM recommendations for specific crops and disease. problems in your area.
Top 3 Diseases Impacting Dry Beans
- White Mould (Sclerotinia sclerotiorum), for a full description go to Foliar Diseases.
- Root Rot Diseases (Seed Rot, Seedling Blight, Root Rot, Rhizoctonia Root Rot, Fusarium Root Rot, Aphanomyces Root Rot), for a full description go to Seed or Soil-Borne Diseases.
- Common Blight and Halo Blight – for a full description go to Foliar Diseases.
- Alberta Blue Book – Crop Protection 2020
- Canadian Plant Disease Surveys
- Dry Bean Disease & Insect Identification & Scouting Guide
- Fungicide Decision Tool for Managing White Mould in Dry Bean
- Maximum Residue Limits
Special thanks to Saskatchewan Pulse Growers and Manitoba Pulse Growers.