How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Seedlings may wilt in fields where inoculum is high. More commonly, symptoms are expressed after fruit set and consist of yellowing of a runner on one side of the plant followed rapidly by wilting of the infected runner. Runner lesions develop externally and extend from the crown to the yellowed tips. Other runners collapse in a similar manner and whole plant collapse occurs rapidly. External lesions may develop on roots accompanied by red gumming at or just below the soil surface. Internally, a dark red-brown vascular discoloration extends from roots to runners.

COMMENTS ON THE DISEASE

The pathogen can cause a serious disease of susceptible varieties. It attacks only varieties of Cucumis melo (i.e., melons and muskmelons) and weeds are not considered to be a host. In California, race 2 predominates but race 1 occurs in limited areas of Merced, Fresno, and King counties. The pathogen survives in soil as chlamydospores, which are thick-walled asexual spores that can survive in soil for over 20 years. The fungus enters plants through roots and disease develops rapidly when soil temperatures are warm.

MANAGEMENT

Resistance to race 2 is available and should be used in fields with a history of the disease. Most cultivars currently in use in California do not have resistance to race 1. Steam clean equipment after working in an infested field. Crop rotation isn't very effective: rotation for 20 years did not work entirely although the disease level was reduced.

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
W. D. Gubler, Plant Pathology, UC Davis
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier

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