Walnut blight
Xanthamonas campestris
What is Walnut blight (Xanthomonas arboricola)?
Walnut blight, caused by Xanthomonas arboricola previously known as Xanthamonas campestris is a bacterial disease that primarily infects English walnut trees. Symptoms include black lesions on catkins, shoots, and leaves. Infected nuts develop black, sunken lesions at the flower end (end blight), progressing to lesions on the sides as they mature (side blight).
How does Walnut blight (Xanthomonas arboricola) occur?
It reproduces through bacterial cells present in infected plant tissues and cankers. The bacteria overwinter primarily in dormant buds. Rain plays a critical role in spreading the bacteria and aiding infection. Splashing rain, wind, or insects facilitates entry into the tree through natural openings or wounds.
Symptoms
1 - Impacts on Plants
Xanthomonas arboricola causes significant damage to walnut trees, reducing nut quality and yield, thereby impacting the overall health and productivity of the plants and affecting the economy.
Solutions
1 - Prevention
• Use disease-resistanttree varieties when available. • Practice good orchard sanitation by removing and destroying infected plant debris and fallen nuts. • Promote good airflow and sunlight penetration within the orchard through proper tree spacing and pruning. • Avoid overhead irrigation methods that create a conducive bacterial growth and spread environment.
2 - Treatment
• Apply protective sprays during critical periods of infection, targeting buds, flowers, and developing nuts. Consult with local agricultural extension services for recommended bactericides. • Consider using spray prediction models, such as XanthoCast, to aid in determining the need for additional treatments. • Implement a regular spray schedule, particularly during prolonged wet springs. • Monitor the disease levels and adjust treatment frequency based on disease risk assessments.
