Diaporthe dieback

Diaporthe dieback is a serious fungal disease caused by the ascomycete Diaporthe nobilis (formerly known as Phomopsis nobilis). This pathogen acts primarily as a bark-colonizing fungus that disrupts nutrient and water transport within the host plant. It often affects plants that have been stressed by environmental factors, drought, or poor cultivation practices.

The host range of this fungus is extensive, including a variety of woody ornamentals, fruit trees such as citrus, and laurel species. The pathogen survives in dormant infected tissues and crop debris, allowing it to remain present in nurseries and gardens from one season to the next, waiting for favorable conditions to infect new growth.

Symptoms typically start as localized necrotic spots on twigs or small branches, which eventually expand into larger, sunken lesions. As the infection progresses, the leaves above the affected area may wither, turn yellow, and drop prematurely. In advanced stages, small, pinhead-sized black fruiting bodies called pycnidia emerge from the bark, serving as the source of inoculum for further spread.

Disease development is highly dependent on humidity levels and temperature. Spore production is prolific during wet, mild weather, and the spores are easily dispersed by rain splashes or wind to healthy susceptible tissues. In addition to natural vectors, the pathogen is frequently spread by contaminated pruning tools and the movement of infected nursery stock across different regions.

The impact of Diaporthe nobilis on plant health can be severe, causing branch death and potentially killing the entire plant if left untreated. Integrated pest management strategies are crucial for control:

• Pruning out infected branches well below the necrotic area.
• Sterilizing all cutting tools with alcohol or bleach after each use.
• Applying preventative fungicides to protect wounds after pruning.
• Improving site hygiene by removing and burning all infested plant material.