How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms of Fusarium wilt usually appear on medium-aged or older plants and begin as a yellowing and wilting of the lower leaves, sometimes more pronounced on one side of the plant. The wilting and yellowing then progress up the plant until the entire plant turns yellow. At this stage, the yellow plants are readily observed in the field. Plants also may be stunted, particularly if infected at a younger age.

The root and stems show few external symptoms (in contrast to Fusarium root rot caused by F. solani). Infected plants often have a swollen root compared to uninfected roots but otherwise may appear healthy on the surface. Discoloration of the vascular system is a diagnostic symptom of Fusarium wilt, and it can be readily seen by cutting into the lower stem and looking for a red-brown streaking in the vascular tissues. The discoloration is usually present in plants showing foliar symptoms and is particularly evident in the lower stem and at stem and petiole nodes.

COMMENTS ON THE DISEASE

Fusarium wilt has been a major problem in California blackeye production. It is the reason why the variety CB 5 was replaced in the 1980's by CB 46 which is resistant to the race 3, the predominant race of Fusarium oxysporum in the state. The pathogen is a specialized form of F. oxysporum that infects only cowpea but not lima beans, common beans, soybeans, or other crops. Like other Fusarium wilt pathogens, it can survive in soil for long periods of time, and continued cropping of blackeyes will result in the build-up of soil populations of F. oxysporum f. sp. tracheiphilum . It also has been reported to be an external contaminant of seed, which has likely facilitated the long distance dissemination of the pathogen.

MANAGEMENT

At this time in California, variety selection is the recommended management. CB 46 is resistant to Race 3, the most common race of Fusarium oxysporum in CA but is susceptible to Race 4, which has been identified in a few locations. Whenever practical, take efforts to minimize spread of the pathogen from infested to uninfested fields via farm machinery, irrigation equipment and water, and contaminated seed. If resistant plants are infected with root knot nematodes, then they may become susceptible. New varieties are being developed with resistance to both Race 3 and 4 and root knot nematode.

PUBLICATION

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Diseases
R. M. Davis, Plant Pathology, UC Davis
C. A. Frate, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Abiotic Disorders:
A. E. Hall, Botany and Plant Sciences, UC Riverside
Acknowledgment for contributions to Diseases/Abiotic Disorders:
S. R. Temple, Plant Sciences, UC Davis
Acknowledgment for contributions to Diseases (viruses):
R. L. Gilbertson, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases (Late-season decline):
J. Deelo, Plant Sciences, UC Davis

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