How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Symptoms of Fusarium yellows or wilt usually appear on medium-aged or older plants and begin as a yellowing and wilting of the lower leaves. 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). Discoloration of the vascular system is a diagnostic symptom of Fusarium yellows, 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 yellows was first described in California in 1928 and it has subsequently spread throughout the United States and into Central and South America. Although the disease is not uncommon in California, it has not become a major problem. The pathogen is a specialized form of F. oxysporum that infects common bean but not lima beans, cowpeas, soybeans or other crops. Like other Fusarium wilt pathogens, it can survive in soil for long periods of time, and continued cropping of bean will result in the build-up of soil populations of F. oxysporum f. sp. phaseoli. 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, specific control measures for Fusarium yellows are usually not used. However, many of the controls recommended for Fusarium root rot may minimize Fusarium yellows, such as crop rotation and seed treatments. 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. Resistance to Fusarium yellows has been identified in a number of bean accessions and could be incorporated into California varieties if the disease becomes a major problem.

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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