How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

If inoculum levels of Fusarium are high, seedlings may wilt in the field. More commonly, however, Fusarium wilt symptoms occur after fruit set and consist of yellowing and wilting of one runner or one side of the plant. External lesions on the runner extend from the crown to the runner tip, which is bright yellow. Other runners soon collapse and the plant dies. External lesions may develop on roots accompanied by red gumming at or just below the soil surface. Internally a dark vascular discoloration occurs.

COMMENTS ON THE DISEASE

There are three races of Fusarium oxysporum f. sp. niveum, but only Race 1 occurs in California. There is polygenic resistance to Race 1 in many varieties, but high inoculum levels can overcome the resistance. It is common to find a few infected plants in a field even if a resistant variety is grown.

MANAGEMENT

Use resistant cultivars. To reduce the inoculum load, it is necessary to rotate out of watermelon for 10 years, because the fungus may reproduce on resistant watermelons even if there are no wilt symptoms.

PUBLICATION

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Diseases
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
B. J. Aegerter, UC Cooperative Extension, San Joaquin County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgment for contributions to Diseases:
W. D. Gubler, Plant Pathology, UC Davis

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