How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

This particular Fusarium wilt only affects blackeye beans and other cowpea varieties. Symptoms usually first appear 6 weeks after planting, with diseased plants having pale green, flaccid leaves that turn yellow and drop off. Subsequently, patches of plants in the field will die, whereas surrounding plants that are not infected still retain green leaves and continue to grow and produce pods. Diagnosis involves slicing the tap root, stem, and branches with a sharp knife. Susceptible, infected plants will have a brown discoloration in the vascular tissue in the center of the root and stem, reaching the branches in some cases. Resistant varieties may have some brown discoloration in the vascular tissue of the roots, but not in the shoots. Susceptible, infected plants that have not died can exhibit a distinct swelling of the base of the stem and adjoining tap root.

COMMENTS ON THE DISEASE

This fungus survives in soil indefinitely, and crop rotation has not been shown to be adequately effective in suppressing the disease. Susceptible varieties can exhibit greater damage due to Fusarium wilt in the presence of root knot nematodes. In this case, soil fumigation with nematicides may increase bean yield, but it will not sufficiently suppress the levels of Fusarium in the soil. Four races of this Fusarium have been identified, but only races 3 and 4 have been detected in California, with race 3 being more widespread.

MANAGEMENT

Races 3 and 4 of Fusarium continue to spread to new fields in California in contaminated soil moved on equipment, during flooding or irrigation, or on the surface of seeds that are contaminated during threshing. The traditional variety CB-5 is susceptible to races 3 and 4 of Fusarium. Use resistant varieties in fields where the disease has been identified. The major blackeye variety grown in California, CB-46, is resistant to the commonly encountered race 3 of Fusarium and yields as well or better than CB-5. CB-46 has a compact, erect growth habit and smaller seed than CB-5. If symptoms of Fusarium wilt occur on CB-46, race 4 may be present in the field. Variety CB-27 is resistant to races 3 and 4 of Fusarium. CB-27 also has resistance to a broader range of root knot nematodes than CB-46 or CB-5. In some conditions, CB-27 is more compact and less vigorous than CB-46 and should be grown on 30-inch rows where it has first-flush yields that are similar to CB-46. CB-27 is a typical blackeye bean but has a bright white seed that is larger than CB-46 but smaller than CB-5.

PUBLICATION

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Diseases
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Abiotic Disorders:
A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to virus sections in Diseases:
R. L. Gilbertson, Plant Pathology, UC Davis
Acknowledgment for co-authorship of Ascochyta Blight:
C. A. Frate, UC Cooperative Extension, Tulare Co.

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