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Phytophthora root rot and crown rot (Phytophthora spp.) is a water mold disease that affects roots and crowns of raspberry, especially red raspberry. The first visible symptoms include wilt of both primocanes and floricanes soon after spring leaf emergence. In less severe situations, slow symptom development occurs with gradual chlorosis, wilting, and dieback during summer. Affected floricanes produce weak lateral shoots that may scorch along leaf margins and between veins. Water-soaked lesions are often visible at bases of affected plants. Scraping off the epidermis (bark) reveals characteristic red discoloration and necrotic (dead) cortical (inner) tissue. Necrosis sometimes expands into crowns. This pathogen favors soils with high moisture content, especially where soil is clay, poorly drained, or rain/irrigation keeps soil saturated for extended periods. Symptoms first appear on plants in low-lying areas and then expand upward or outward. High soil moisture accelerates pathogen reproduction and rate of infection. Some Phytophthora species have broad host ranges and may be present in soils prior to raspberry planting. Other species have more restricted host ranges and are likely introduced into planting sites via infected plant material. Once Phytophthora is established in soils, it persists for many years after host plants are removed.

Phytophthora root and crown rot symptomatic plants.

(Photo: HJ Larsen, Bugwood.org)

Infected roots with characteristic red discoloration.

(Photo: Wayne Wilcox, Cornell University)

Management:

• Select a growing site with good soil drainage and plant onto raised beds.
• Begin with disease-free stock plants.
• Consider selecting resistant cultivars.
• Rotate with non-susceptible crops, if needed.
• Apply fungicides to suppress disease if site has a history of disease.

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