Hendersonula branch wilt

Hendersonula branch wilt, caused by the fungus Neoscytalidium dimidiatum (syn. Hendersonula toruloidea), is a destructive disease affecting the vascular system of woody plants. The pathogen colonizes the branches and trunk, ultimately blocking the flow of water and nutrients, which results in characteristic wilting and dieback.

While the disease is particularly notorious for its impact on Citrus species, it also affects a wide array of hosts, including almonds, walnuts, and various ornamentals. The fungus acts as a facultative parasite, meaning it can survive on dead plant debris, making it a persistent threat in orchards.

Symptoms typically include bark discoloration, the formation of cankers, and significant gumming on affected branches. When the bark is peeled back, one can often see a layer of dark, powdery spores, which is a diagnostic sign of the pathogen's presence and activity.

Environmental conditions such as high temperatures and water stress are the primary drivers of disease progression. The fungus invades the plant through wounds caused by pruning, insects, or environmental damage, and spreads through the air as spores or via contaminated agricultural equipment.

The economic impact of this disease is significant, as it can lead to the total decline of infested trees if not managed properly. Effective strategies for control include:

• Strict sanitation by pruning and destroying infected branches well below the visible lesion.
• Disinfecting pruning shears and saws with alcohol or bleach after each cut.
• Maintaining tree vigor through appropriate irrigation and nutrient management.
• Applying protective copper-based fungicides to pruning wounds.