Avocado Diseases
Avocado diseases can result from fungal, bacterial or viral infections. Of these, fungal diseases are by far the most numerous. The point of attack can vary from the roots, leaves or trunk to the fruit. The symptoms may be similar – for example small and deformed leaves or wilting can occur as a result of many different fungal infections. A tree that is small, with few leaves and low yields, is more likely to be suffering from environmental problems than disease.
Disease Symptoms
- A healthy avocado tree has glossy, dark green leaves, intact bark and plenty of blossoms. Common symptoms of disease include:Leaves: small leaves that are pale green, yellowed, blotched or blackened. Leaves may turn brown but hang on the branches for months. Few leaves or excessive leaf fall.
- Trunk/Bark: Mottled, streaked, cracked or rough bark. Bark may peel back easily or exude a white powder. Cankers may be present.
- Fruit: Black spots, rotting (interior or exterior), early fruit drop or deformed fruit.
- External: Mushrooms and other fungal growths may appear on the trunk or around the base of the tree, particularly after watering or a heavy rain.
Environmental Conditions
Since avocados never go dormant, growing conditions and moisture levels are critical to keeping the tree healthy. Certain environmental conditions can predispose to disease, especially fungal diseases. Although avocados prefer moist soil as they do not sink deep roots, too much water greatly increases the risk of disease. Drip irrigation is preferred, partly to prevent over-watering and partly to keep bark dry. Trees that are stressed or have nutrient deficiencies are more susceptible to disease.
Preventing Avocado Disease
Disease prevention begins with good drainage, especially in preventing fungal diseases. Avoid over-watering – soils should be uniformly moist but not wet, to ensure proper oxygenation. Choose nursery stock that is certified disease-free and select resistant rootstocks. Provide adequate nutrients in the form of fertilizer and/or compost. Fungicides can help prevent or treat infection – obtain expert advice before using.
