What is Scab on Avocado Fruit?
Avocado scab disease is caused by the fungus Sphaceloma perseae. Scab symptoms on avocadoes present as oval to round, raised areas of corky scab. The first lesions that appear are generally black/brown and scattered across the fruit’s skin. The lesions begin to coalesce and merge, potentially affecting almost the entirety of the fruit. Symptoms of scab on the leaves are more difficult to ascertain, as the most visible signs are in the uppermost portions of the tree’s canopy. Young leaves may become distorted and stunted with reddish spots on both the upper and lower sides of the foliage. Scab symptoms on avocado may be confused with physical damage. Fruit is most susceptible right after fruit set and during the early stages of development. When the fruit is at about half its mature size, it becomes resistant to the infection, as do leaves once they are about a month old. The disease is most prevalent after long periods of rain, especially when the tree is in its initial stages of fruit set.
Avocado Scab Control
Although the disease is primarily cosmetic, affecting the exterior of the fruit but not the interior, it is a portal for other diseases, so treating avocado scab before any sign of infection is necessary to the health of the tree and resulting fruit. Also, since scab is spread by the dispersal of spores produced at the early stages of infection and then spread through the movement of wind, rain, and tools or equipment, the pathogen can travel over long distances. Fungicides should be used to mitigate the spread of the fungus. Treatment involves the application of copper fungicide when flower buds appear, near the end of bloom time and again 3-4 weeks after.
