How to Manage Pests
UC Pest Management Guidelines
Phytophthora Root Rot
Pathogen: Phytophthora parasitica and P. capsici
(Reviewed 12/13, updated 12/13)
In this Guideline:
The most distinctive symptoms of Phytophthora root rot are the brown lesions on roots of all sizes. The xylem of the roots above the lesions often turns yellowish or brown. In severe cases, nearly all roots may be girdled or rotted off. Aboveground, infected plants are slow growing and may wilt or die in hot weather. When fruit in contact with the ground are infected, the disease is called buckeye rot. Symptoms include tan or brown spots with concentric rings. Phytophthora capsici also causes greasy, purple-brown stem lesions.
Comments on the Disease
Phytophthora parasitica and P. capsici occur in most soils. Infection of plants occurs at any stage of growth when there is free water in the soil. Damage is greatest in poorly drained, compacted, or overirrigated soils.
Good water management is key to managing this disease and avoiding the need for fungicide treatments.
Provide good drainage and prevent flooding. Avoid wide fluctuations in soil moisture, which predisposes plants to infection. Keep tops of bed dry to avoid buckeye rot of the fruit. Planting cereals as a rotation crop may reduce the level of infestation in the soil. Resistant varieties are not yet commercially available.
Organically Acceptable Methods
Cultural control is acceptable in an organically certified crop.
Fungicides are needed only in poorly drained soils or where root rot is historically a problem.
UC IPM Pest Management Guidelines: Tomato
R. M. Davis, Plant Pathology, UC Davis