How to Manage Pests
UC Pest Management Guidelines
Crown and Spear Rot
Pathogens: Phytophthora megasperma var. sojae and other Phytophthora spp.
(Reviewed 6/09, updated 6/09)
In this Guideline:
SYMPTOMS AND SIGNS
Phytophthora spear rot is characterized by soft, water-soaked lesions on shoots at, slightly above, or below the soil level. The lesions elongate rapidly and become light brown. As the lesion collapses and shrivels, the affected side of the spear becomes flattened, and the shoot becomes extremely curved and may even collapse. This symptom is not diagnostic, however, as insect and mechanical injury can result in crooked spears. Infected young storage roots appear water soaked but firm.
Crowns infected with Phytophthora spp. have yellow-orange colored tissue. In severe infections the tissue appears waterlogged and fibrous.
COMMENTS ON THE DISEASE
Phytophthora is a soilborne fungus; it infects the shoot near or just below the soil line during very wet periods. Heavy spring rains can induce severe disease losses. Although crown and spear rot is erratic in California, the fungus is present in all production areas of the state. Desert areas, however, usually escape the disease unless conditions are unusually wet. Infected spears, if hydrocooled during packing for market, may contaminate the water and spread the pathogen to other spears, causing extensive rot during transit.
Whenever possible, plant in Phytophthora-free soil and use disease-free transplants. Provide good drainage and do not overwater. If symptoms occur, treatment may be necessary.
Organically Acceptable Methods
Avoid Phytophthora-infested soils and use disease free transplants when growing an organically certified crop.
UC IPM Pest Management Guidelines:
Acknowledgment for contributions to Diseases: