avocado scab

Plants affected

• avocado

Easily confused with

• anthracnose

  How to tell them apart: Avocado anthracnose (Colletotrichum gloeosporioides) starts as small brown specks on leaves and fruit but the fruit lesions deepen into circular, SUNKEN, dark-brown to black spots that soften and may show salmon-pink spore masses in humid weather; rot extends into the flesh, especially after harvest. Avocado scab (Sphaceloma persae) instead makes lesions that stay SUPERFICIAL and RAISED — corky, rough, brown to purplish oval scabs with a star-shaped cracked surface — that stay on the skin and do not rot the flesh. The key field tell: press the lesion. Anthracnose is sunken and soft; scab is raised, dry and corky. On leaves scab also causes small holes and distorted, puckered young foliage, which anthracnose does not.

• avocado cercospora spot

  How to tell them apart: Pseudocercospora purpurea (avocado cercospora spot) makes small, flat, angular-to-irregular brown lesions on both leaf surfaces and on fruit; the spots stay sunken or level with the skin, often have a faint purplish margin, and on fruit they may crack and join into larger dark blotches without ever rising above the surface. Sphaceloma persae (avocado scab) instead produces lesions that quickly become raised, corky and rough: on fruit you see scattered brown-to-purplish spots that turn into hard, scabby, often star-shaped corky islands you can feel with a fingertip, and on leaves the spots are smaller, oval and tend to drop out leaving shot-holes along the veins. The decisive test is texture: run a finger over the lesion. Cercospora is smooth and flat; scab is rough and raised. Scab is worst on young expanding fruit and flushing leaves in wet, humid spring weather, while cercospora spotting builds up later on older leaves and maturing fruit.

Common questions

Do I have to report avocado scab?

No. avocado scab is not a notifiable organism, so there is nothing to report to an authority. Treat it as a normal garden problem.

How is avocado scab treated?

Mainly with biological and cultural measures — removing affected material, changing the conditions that favour it, and treating with agents approved in your country. The exact steps and their timing depend on the plant, the season and where you live: Dr. Phyto works them out in a free diagnosis.