Shallow bark canker

The causative agent of the disease is the bacterium Brenneria nigrifluens. This plant pathogen is primarily known for causing bark canker in walnut trees, leading to tissue necrosis that compromises the vascular system and overall vitality of the tree.

The disease primarily affects walnut trees (Juglans regia). While it can occur in various orchard conditions, it poses the greatest threat to established trees, often impacting productivity and structural integrity in commercial nut plantations worldwide.

The typical symptoms include longitudinal cracking of the bark on the trunk and primary limbs. A dark, blackish fluid (exudate) frequently oozes from these cracks during the growing season. Beneath the affected bark, necrotic lesions form, often spreading laterally and eventually girdling the branches or trunk.

• Prolonged periods of high humidity and rainfall.
• Mechanical injuries to the bark caused by farm equipment or improper pruning.
• Optimal temperature ranges that favor rapid bacterial multiplication.
• Lack of proper orchard sanitation and pruning tool sterilization.

The damage caused by Brenneria nigrifluens is severe, often resulting in limb dieback and reduced nut production. If the cankers girdle the trunk completely, the entire tree can perish. This leads to significant economic losses for growers who must manage or replace affected orchard blocks.

Management strategies focus on prevention and sanitation. Pruning should be performed during dry weather to prevent infection entry. Infected bark and limbs must be carefully removed and destroyed. Preventive sprays with copper-based compounds can help manage bacterial populations on the bark surface and limit the spread of the pathogen.