Common Blight of Bean

Common Blight of Bean

Common blight also referred to as common bacterial blight is a major disease of bean in the U.S. (east of the Rocky Mountains) and many other parts of the world. The causal organism of this disease is Xanthomonas campestris pv. phaseoli (Smith) Dye. The bacterium infects many types of beans including snap, field, hyacinth, lima, moth, mung, Scarlet runner and Tepary. In addition to beans, white flowering lupine and fenugreek are susceptible hosts. X. campestris pv. phaseoli overwinters primarily in and on infected seed. Bacterial cells in the seed are able to remain viable longer that the seed itself. In temperate climates it may also overwinter on infected plant debris, with the best rate of survival occurring in debris remaining on the soil surface under dry conditions. Bacteria associated with the seed provide a source of primary inoculum for both local and long distant spread of the disease while infected debris (including cull piles) is more important in local spread of the disease. Infection and disease development is favored by warm (28-32^oC), wet weather. Seedlings grown from infected seed develop lesions containing bacteria on their stems, cotyledons and first set of primary leaves. The bacteria in these lesions are commonly spread by wind blown rain and infects other bean plants via stomata, hydathodes and wounds. Other means of bacterial dispersal include wind blown dirt particles, contaminated irrigation water, physical contact between plants, humans and animals and insects including white flies and certain other leaf feeding insects. Once the disease is established, numerous lesions are produced on aerial plant parts as serve as an inoculum source for secondary spread of the disease. Seed may become infected in two ways: the bacterium may enter the seed via the vascular system or by external pod infections. The bacterium is also capable of growing epiphytotically on weedy hosts.

Symptoms

Common blight symptoms are initially visible as small water-soaked spots on leaf margins or between the veins. Spots eventually dry and turn brown. They are surrounded by narrow band of lemon yellow tissue. Spots enlarge with age and blight large areas of leaf tissue. Heavily infected leaves may become tattered when wind whipped. In severe cases they die and remain attached to the plant. Pod infections also begin as water-soaked spots. Pod lesions may be reddish-brown at the margins or in entirety. A slimy bacterial exudate may be present in pod lesions. The exudate eventually dries giving the lesion a glazed appearance. Pod lesions ultimately turn brown and vary in size depending on the age of the pod when infection occurs. In severe cases the entire pod shrivels. Seed produced from infected plants may be shriveled, discolored or nonexistent if a severe pod infection occurs. Infected seed produced on white-seeded varieties generally shows some degree of yellow discoloration and appears shiny. Some very distinctive symptoms are associated with this disease, however, it important to note that the bacterium can be present in large numbers on symptomless hosts and can still serve as a source of secondary inoculum from these hosts.

Plant Health Management

Use pathogen free seed

In the United States this seed is generally grown west of the Rocky Mountains

Use Disease Tolerant Varieties

There are no varieties available that are totally resistant to common blight but some varieties of dry bean that are tolerant have been developed by researchers (Drs. Coyne and Schuster) In the Horticulture Department at the University of Nebraska. Tara, Valley and Jules are Great Northern types that show varying degrees of tolerance to the disease.

Crop Rotation

Allow at least 2 years between bean crops

Apply Copper Fungicides

Avoid working and fields and gardens when foliage is wet

Eliminate alternate hosts including weeds and volunteer beans

References

Hall, R. ed. 1991. Compendium of bean diseases. American Phytopathological Society. St. Paul, MN. 73 pp.

Schwartz, H.F. and G.E. Galvez, eds.1980. Bean production problems: disease, insect, soil and climatic constraints of

Phaseolus vulgaris. Centro Internacional de Agricultura Tropical (CIAT), Cali, Columbia. 424 pp.

Sherf, A.F. and A.A. Macnab.1986. Vegetable diseases and their control. John Wiley & Sons. New York, NY. 728 pp.

Useful Links

University of Guelph, Canada

Highlighted Area

Common blight is often found in association with fuscous blight, another bacterial disease of bean. The symptoms and epidemiology of the diseases are the same. The causal organisms of the two diseases also have the same scientific name. The only distinguishing characteristic between the two is that one produces a brown pigment in culture (fusdous) and one does not (common). Since the two diseases occur simultaneously in many cases, it has been difficult to asses the amount of yield loss caused by each individual disease.

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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