Thousand Cankers Disease

Thousand Cankers Disease (TCD) is a serious and often fatal disease affecting walnut trees, primarily black walnut (Juglans nigra), though other walnut species can also be affected. The disease is caused by a complex interaction between a fungal pathogen, Geosmithia morbida, and the walnut twig beetle (Pityophthorus juglandis), which acts as a vector for the fungus.

Symptoms

1. Cankers on Twigs and Branches: The primary symptom is the appearance of numerous small, sunken lesions or cankers on the branches and twigs of walnut trees. These cankers are often surrounded by a yellow or brown discoloration.
2. Dieback: As the disease progresses, the affected branches may experience dieback, which can eventually lead to the death of entire limbs.
3. Reduced Growth: Trees suffering from Thousand Cankers Disease may exhibit reduced growth, thinning canopy, and overall decline in health.
4. Woodpecker Damage: Woodpeckers may be attracted to the affected trees and cause additional damage as they search for beetle larvae beneath the bark.

Disease Cycle

1. Beetle Activity: The walnut twig beetle carries the Geosmithia morbida fungus and introduces it into the tree when feeding and laying eggs. The fungus then spreads through the vascular system of the tree.
2. Fungal Growth: The fungus causes the formation of cankers, which disrupt the flow of water and nutrients within the tree, leading to dieback and decline.
3. Spread: The disease spreads through beetle activity and the movement of infected wood or plant material. It can also be spread by planting infected nursery stock.

Management

1. Preventive Measures
   • Avoiding Infested Wood: Do not transport or move walnut wood from areas known to have Thousand Cankers Disease, as this can spread the disease to new areas.
   • Monitoring and Early Detection: Regularly inspect walnut trees for signs of the disease, such as cankers and woodpecker damage. Early detection can help in managing the disease more effectively.
2. Cultural Practices
   • Proper Pruning: Prune out and properly dispose of affected branches to reduce the spread of the disease. Ensure pruning tools are disinfected to prevent cross-contamination.
   • Healthy Trees: Maintain overall tree health through proper watering, fertilization, and pest management to help trees withstand stress and disease.
3. Chemical Control
   • Insecticides: Insecticides may be used to control the walnut twig beetle. Consult with a local extension service or a professional arborist for recommendations on effective products and application methods.
   • Fungicides: Currently, there are no effective fungicides for controlling Geosmithia morbida once it is inside the tree. Management focuses on controlling the beetle and removing infected material.
4. Research and Extension
   • Stay Informed: Keep up-to-date with research and guidelines from local agricultural extension services or forestry departments. They may offer new strategies or management practices for dealing with Thousand Cankers Disease.