Nattrassia disease

Nattrassia disease is a serious fungal infection affecting a wide range of woody plants, caused by the pathogen Nattrassia mangiferae (formerly known as Hendersonula toruloidea). This fungus is a opportunistic pathogen that thrives in warm and arid environments, impacting both orchard crops and ornamental trees.

Host plants commonly affected by this pathogen include mango, grapes, citrus species, walnuts, and almonds. The infection typically establishes itself through entry points such as pruning wounds, mechanical bark damage, frost cracks, or sites affected by sunscald, where the tree's natural defense barriers are compromised.

The primary clinical signs include bark necrosis, canker formation, and severe branch dieback. As the fungus colonizes the inner bark and cambium, it often produces a characteristic dark, powdery mass of spores under the outer bark layers. Affected branches eventually lose their foliage, become brittle, and may perish if the disease girdles the branch or trunk.

Environmental conditions play a critical role in the severity of the disease. Prolonged drought and excessive heat stress the trees, significantly reducing their ability to compartmentalize the infection. The spores are primarily dispersed by wind and splashing water, while contaminated pruning tools represent a major vector for spreading the disease within an orchard.

Management strategies focus on minimizing host stress and preventing the spread of inoculum:

• Regular pruning of infected branches with immediate disposal (burning).
• Strict sanitation of tools using disinfectant solutions between trees.
• Application of white latex paint to trunks to prevent sunscald.
• Proper irrigation management to maintain tree vigor during heat waves.
• Use of copper-based fungicides during the dormant season to reduce spore pressure.