Chestnut phytophthora

Pathogen and type of disease. This disease is caused by the oomycete Phytophthora castaneae, a serious pathogen that attacks the root system and the root collar of chestnut trees. Often referred to as a root rot or collar rot, it is an soil-borne infection that can survive in the environment for years, making it difficult to eradicate once it is established.

Susceptible crops. The primary host for this pathogen is the genus Castanea. It poses a significant threat to commercial chestnut orchards, as well as native forest trees and ornamental chestnut varieties. The susceptibility varies depending on tree age and environmental stress, but all chestnut species should be considered at risk.

Symptoms and signs of infection. Infected trees exhibit canopy thinning, chlorosis of leaves, and dieback of branches. The most diagnostic sign is the presence of brown, sunken necrotic lesions at the base of the trunk or on the main roots. When the bark is removed from the affected area, the inner tissue often appears reddish-brown or water-soaked, indicating active fungal decay.

Conditions for development and severity. Phytophthora castaneae thrives in wet, poorly drained soils where stagnant water allows for the movement of mobile zoospores. The disease spreads rapidly during heavy rainfall or over-irrigation events. The severity of the damage is high, as the destruction of the fine root system prevents the tree from absorbing water and nutrients, leading to rapid decline.

Protection and prevention measures. Integrated management is essential to control the spread of the pathogen:

• Improve soil drainage to eliminate waterlogged areas.
• Implement strict sanitation practices when handling infected tree material.
• Use disease-resistant rootstocks if available for local varieties.
• Apply systemic fungicides containing fosetyl-aluminum or metalaxyl as preventive treatments.
• Regularly monitor the root collar of trees for any signs of discoloration or oozing.