How to Manage Pests
UC Pest Management Guidelines
Pathogens: Various fungi (Acremonium cucurbitacearum, Pythium spp., and Rhizopycnis vagum)
(Reviewed 11/05, updated 6/12)
In this Guideline:
SYMPTOMS AND SIGNS
Symptoms of sudden wilt begin when the crown leaves yellow, followed by a rapid collapse of the entire plant. Plant death quickly proceeds across a field. Pythium spp. cause a watersoaked, brown root rot. Acremonium causes corky bands on primary and secondary roots. Infected roots are straw colored or slightly darker than healthy roots. Rhizopycnis causes a reddish tinge to the upper tap root. Infected tissue may be corky.
COMMENTS ON THE DISEASE
All pathogens are soilborne. The disease usually occurs just before harvest, and the foliage and roots in affected fields may appear healthy for the majority of the season. Pythium infection generally follows a period of cool weather, rain, or heavy irrigation. However, in low desert production areas, P. aphanidermatum and P. myriotylum often cause sudden wilt, and both of these pathogens are favored by warm, wet soil conditions.
Start looking for sudden wilt during the vegetative growth stage.Note infections to make management decisions before the next crop. The disease is unpredictable. The development of the disease occurs so quickly and without warning that control measures are impossible to implement. Practice long-term rotation (at least 2–3 years out of cucurbits) to help prevent the build-up of these pathogens. For Pythium control, provide good drainage and avoid excessive soil moisture by extending intervals between irrigations and avoiding long irrigation periods. Fungicides have not proven effective in controlling sudden wilt.
UC IPM Pest Management Guidelines:
R. M. Davis, Plant Pathology, UC Davis
Acknowledgment for contributions to Diseases:W. D. Gubler, Plant Pathology, UC Davis