Botryodiplodia branch dieback

Botryodiplodia dieback, caused by the fungus Botryodiplodia hypodermia, is a destructive plant disease primarily affecting the bark and cambium of woody plants. As a facultative parasite, the fungus typically attacks trees under environmental stress, rapidly colonizing necrotic tissue and spreading through the vascular system, which leads to branch mortality.

The host range for this pathogen is broad, encompassing various fruit trees and ornamental landscape species, including oaks, elms, and maples. In nurseries and commercial orchards, the presence of the fungus can cause significant economic losses, affecting tree vigor, wood quality, and fruit production potential.

Symptoms of the infection usually appear as elongated, sunken, dark-colored lesions on the branches or stems. Under favorable moisture conditions, the bark erupts with small, black, pin-head-sized fruiting bodies known as pycnidia. As the infection progresses, the leaves distal to the lesion turn yellow and wither, eventually leading to a complete "dieback" appearance of the affected canopy parts.

Environmental conditions play a critical role in the disease cycle. The pathogen thrives in warm temperatures between 20°C and 28°C and requires high humidity for spore production and germination. Mechanical injuries, drought stress, and winter damage significantly increase the susceptibility of trees, providing entry points for the fungus to establish its mycelium.

Managing the disease requires an integrated approach to maintain tree health and suppress the fungal inoculum. Key management practices include:

• Prompt excision of infected branches, cutting well into healthy tissue.
• Sanitizing pruning tools with alcohol or bleach to prevent mechanical disease spread.
• Maintaining optimal irrigation and soil fertility to reduce plant stress.
• Applying protective copper-based fungicides during the dormant season to inhibit initial spore colonization.