Bacterial blight of dry beans in Michigan
Where it comes from, how to spot it, and what to do about bacterial blight on dry beans.
Bacterial blight, a term used to describe similar disease on beans caused by one or more species of bacteria, is an important problem on Michigan dry beans. Common bacterial blight, caused by Xanthomonas campestris pv. phaseoli or Xanthomonas axonopodis pv. Phaseoliand, and halo blight, caused by Pseudomonas syringae pv. Phaseolicola, are normally the most common pathogens. These diseases can overwinter in plant debris from a previous dry bean crop and in bean seed from infected plants. The following year, emerging plants from clean seed can pick up the pathogen and become contaminated. Volunteer beans from a diseased previous crop or seed beans contaminated with these pathogens will harbor the bacteria. The bacteria can also be spread to uninfected plants by wind, rain, irrigation water and contaminated equipment.
Bacterial disease development on dry beans is influenced greatly by environmental conditions and cultural practices. Common bacterial blight is favored by temperatures over 80 degrees Fahrenheit and humid, rainy weather. Halo blight outbreaks are more serious when temperatures are cooler, or below 80 F. Outbreaks often occur a week or so after a period of humid, rainy weather. Hail and high winds, including blowing soil, cause wounds in plant tissue that allow for entry by bacterial pathogens. Cultivation and spraying equipment, as well as field workers and sucking insect pests, can also create wounds with the same results. Spread from plant to plant can be very rapid under warm weather conditions.
Ability to diagnose bacterial disease in dry beans is essential to determining proper corrective actions. A picture tour of dry bean diseases from the Michigan State University Saginaw Valley Research and Extension Center gives a good visual aide, including diseases caused by bacteria, fungi and viruses. Common blight foliar symptoms include small, water-soaked spots on the underside of leaflets that enlarge and merge, becoming dried and brown. A narrow, bright lemon-yellow border of tissue often encircles the lesion. Halo blight symptoms are similar with lesions typically somewhat smaller. Weather conditions can be a useful tool in distinguishing between these two similar diseases. You can also request assistance from your local Michigan State University Extension field crops educator to identify these diseases. The MSU Diagnostic Services lab is also a great option for identifying this and many other crop problems.
Bacterial disease in dry beans can be managed successfully, but not totally eliminated. Here are a few suggestions:
- A three- to four-year rotation with beans planted every third or fourth year. Corn, small grains and vegetables make good rotational crops.
- Proper sanitation of bean crop residue including thorough incorporation of residue into the soil and elimination of any volunteer beans the following year. Residue from diseased beans may also be found in bean “dust” on contaminated harvest, seed-cleaning and storage equipment.
- Always plant certified seed and treat seed with streptomycin if bacterial disease problems are anticipated.
- Avoid cultivation of beans when plants are wet or when plants are too tall to allow cultivation equipment to pass by without causing plant injury. Thoroughly clean equipment before moving to another field.
- Avoid reuse of irrigation runoff water.
- Use varieties resistant to common and halo blight if available.
- Copper-based bactericides may be used, but have had limited effectiveness as suppressing these diseases in the field.
The dry bean section of MSU Extension Bulletin E1582, “Insect, Nematode, and Disease Control in Michigan Field Crops,” contains good descriptions and control suggestions for common dry bean disease problems in Michigan, including common blight and halo blight. Note: There are parts of this publication that need updating.
For more information, contact your MSU Extension field crops educator.