By: Liz Baessler
Beans are some of the most gratifying vegetables you can have in your garden. They grow vigorously and reach maturity quickly, and they produce new pods all through the growing season. Keep reading to learn more about bacterial blight of beans and the best methods of bacterial bean blight treatment.
Bacterial Blight of Beans
There are typically two types of bacterial blight affecting bean plants the most – common blight and halo blight.
Common blight in beans is the most prevalent of bacterial bean diseases. Also called common bacterial blight, it shows up in misshapen leaves and pods. The leaves first start to develop small wet lesions that grow in size and dry out, usually becoming over an inch (2.5 cm.) wide, brown and papery, with a yellow border. These spots usually stretch to the edges of the leaves. The pods develop similar wet patches that then dry and shrivel, and the seeds inside are usually small and malformed.
Common blight is often spread through moisture. The easiest and most effective way to prevent its spread is to avoid coming into contact with your plants while they’re wet. It’s also a good idea to control weeds and pests, like beetles and whiteflies, which are known to spread the bacteria.
Controlling common bacterial blight of beans isn’t always easy. If a plant does become infected, it may be best to remove and destroy it to prevent further spread.
Halo blight is the second of the major bacterial bean diseases. Its symptoms are similar to those of common blight and begin as small wet lesions on the leaves. The lesions will turn red or brown and are surrounded by a much larger yellow ‘halo.’ Unlike with common blight, these lesions stay very small. The pods are affected in much the same way as with common blight.
Prevention and treatment methods are basically the same as well – try to keep foliage dry and don’t touch it when it’s wet. Try not to wound the plants, as this is how the bacteria gets inside. Keep weeds and pests to a minimum. As with treating common blight in beans, destroy affected plants.
Spraying copper based bactericides should stop the spread of bacteria and is a good preventative measure for containing eventual outbreaks of both types of bacterial blight of beans.
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Where it comes from, how to spot it, and what to do about bacterial blight on dry beans.
Bacterial blight on dark red kidney bean foliage, Aug 15, 2012. Photo credit: Fred Springborn, MSUE
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.
This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).
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There are three bacterial diseases of bean which are very similar, Common Blight (Xanthomonas campestris pv. phaseoli), Halo Blight (Pseudomonas syringae pv. phaseolicola), and Fuscous Blight (a variant of X. campestris pv. phaseoli). In general, they affect only beans and closely related plants. The host range for Common Blight includes field and snap beans, lima bean, Scarlet Runner bean, hyacinth bean, soy bean, mung bean, Tepary bean, urid bean, moth bean, white flowering lupine, and fenugreek (Trigonella). Fuscous Blight can affect field and snap beans, civet bean, and Scarlet Runner bean. Halo Blight affects field and snap beans, especially cranberry, red kidney, and yellow eyed beans. Lima bean and Scarlet Runner bean are also hosts. All three diseases cause symptoms on leaves and pods, and are able to survive in contaminated seed. Halo Blight infection can occur early in the season, and is favored by moderate temperatures (75–83° F). Common Blight and Fuscous Blight occur later in season, and are favored by warmer temperatures (82-90° F).
Symptoms. The symptoms for all three diseases are very similar, and it generally takes an experienced diagnostician to differentiate them. On the leaves, spots begin as small water-soaked areas. As the spots expand, the center dries and the edges often have a narrow bright yellow band, called a halo. The halo may be present in all three diseases, but is usually wider in Halo Blight. The halo may be small or absent in all three diseases as well, especially if the temperature is above 80 F. On a susceptible variety, the spots will continue to expand until they merge, and can take up large portions of the leaf. The unaffected portions of the leaf can survive without drying. The dry centers of the spots may tear and fall out. In Halo Blight, very severe infection may cause defoliation, wilting, and death of the plant. In Common Blight, dead leaves generally stay on the plant. Common Blight may also cause water-soaked spots to appear on the stems at any time during the season, usually at the lower nodes. These may kill the plant if they girdle the stem, or may weaken it so that it breaks off in a storm.
On pods infected with Common Blight or Fuscous Blight, small round water-soaked spots appear which grow to large irregular patches that may have a reddish border or even be entirely reddish. The spots become brown as they age. During very humid weather, there may be a yellowish crust of bacteria on the surface of the spots. Halo Blight causes similar symptoms on pods, although the spots are smaller, sunken, and brown. The bacterial ooze is white. In severe infections with any of these diseases, the entire pod may shrivel, and the seeds may either not develop or be shriveled. In less severe infections, especially if the suture of the pod is not affected, the seeds develop normally although they may be slightly wrinkled or have a yellowish polished appearance, which may be blotchy or follow veins. Seedlings grown from infected seed have the characteristic spots on stems, cotyledons, and first true leaves. Symptoms may appear later if weather is unfavorable for disease development. In Halo Blight, an older plant grown from infected seed will have yellow areas on the leaves between the veins, with the veins remaining dark.
Similar Diseases. Pod symptoms are similar to anthracnose, which causes a tan to salmon-colored ooze to form in the spots, while the bean blights cause white or yellow ooze.
- These pathogens survive in diseased seed, it is important to use ONLY western-grown certified disease free seed. One or two infected seeds in a lot are enough to cause a severe outbreak in the field.
- Use seed that has been treated with antibacterial chemicals as well, since dust from processing may contain the pathogen.
- A rotation of 2 to 3 years with no beans is recommended.
- Avoid working in fields with wet leaves.
- Control weed hosts, which include goosefoot, pigweed, and amaranth.
- Plow after harvest to bury debris the pathogen may survive in debris in mild winters.
- Clean equipment between fields.
- Sanitize equipment if blight has been a problem on a farm.
- Resistance is available for halo blight, but there are not many resistant varieties for common or fuscous blight.
- See current recommendations for chemical control measures.
- Saettler, A. W. Common Bacterial Blight. pp. 29-30 in Compendium of Bean Diseases. R. Hall, ed. APS Press, St Paul, MN. 1991.
- Saettler, A. W. Halo Blight. p. 30 in Compendium of Bean Diseases. R. Hall, ed. APS Press, St Paul, MN. 1991.
- Sherf, A.F. and A. A. MacNab. Vegetable Disease and Their Control. John Wiley and Sons, New York. 1986.
By: Pamela S. Mercure, IPM Program Assistant, University of Connecticut
Updated by: Mary Concklin, UConn IPM. 2012
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.
Other bacterial diseases on green beans
Blight is the most important bacterial disease on green beans, especially bush bean that is planted the most. There are other bacterial diseases but they are not that common and more of academic importance than commercial. The following bacterial diseases occur rarely:
- Bacterial wilt – Corynebacterium flaccumfaciens (Hedges) Dows. – Mostly confined to vascular system.
- Gall blight – Pseudomonas viridiflava (Burk) Clara. Hardly happens in South Africa.
- Bacterial Soft Rot – Ervinia carotovora (Jones) Holland. – Mostly a problem in pack houses as it requires very high humidity to grow.