Lasiodiplodia walnut dieback

Lasiodiplodia walnut dieback (Lasiodiplodia regiae) is a serious fungal disease characterized by necrotic lesions and progressive tissue death in walnut trees. This pathogen is a member of the Botryosphaeriaceae family, known for causing significant decline in orchard health.

The primary host for this disease is the walnut tree (Juglans regia). While it most frequently affects mature trees under stress, nursery stock can also become infected, leading to poor growth and high mortality rates in young plantations.

Symptoms include visible cankers, bark splitting, and the oozing of dark fluids from trunk and branch fissures. Internally, the wood displays dark staining or browning, which indicates the pathogen is colonizing the vascular system, ultimately hindering the tree's ability to transport water and nutrients.

The development of Lasiodiplodia regiae is favored by warm, humid conditions. The fungus acts as a wound pathogen, typically invading the host through pruning cuts, hail damage, sunscald, or insect-feeding sites, which serve as entry points for the fungal spores.

To control the impact of this disease, an integrated management strategy is essential to prevent the pathogen from spreading throughout the orchard. Best practices include:

• Sanitary pruning of infected branches during dry weather to prevent spore spread.
• Sterilization of pruning equipment with ethanol or bleach between trees.
• Application of protective wound sealants on major cuts.
• Maintaining optimal tree vigor to enhance natural resistance to secondary infections.