Why Are My Apples Covered in Sooty Blotch?

Apples harvested with dull, dark grey, olive or smudgy brown blotches on the skin surface — as if someone has rubbed soot across the fruit — have sooty blotch, a superficial fungal surface disease caused by a complex of several fungal species. A related condition, flyspeck, produces groups of tiny black dots (individual fungal fruiting bodies) scattered across the skin surface. Both conditions affect only the outer surface of the skin — the flesh underneath is completely unaffected and perfectly edible. However, the cosmetic damage is significant and makes fruit unappealing for fresh eating or sale.

Conditions that favour sooty blotch

Both sooty blotch and flyspeck require prolonged wet weather and high humidity — a wet summer with extended leaf wetness is the main risk factor. They are more severe in: dense, overcrowded canopies where air circulation is poor and surfaces stay wet longer; orchards with a history of these diseases on surrounding trees and hedgerows; and years with high rainfall from July onward. Both diseases develop slowly — visible symptoms typically appear in late summer as the fungi have had the entire season to colonise the fruit surface.

Can it be removed?

Yes — the fungal growth is on the surface of the waxy cuticle layer and can be scrubbed off with a clean damp cloth or vegetable brush under running water. Wiping firmly removes most of the discolouration. The fruit underneath is clean and sound. Sooty blotch does not penetrate into the flesh and does not affect storage life of otherwise sound fruit.

Prevention

Open the tree canopy with annual pruning to improve airflow through the centre. Avoid creating very dense growth by removing crossing and congested branches. Apply captan, copper or sulphur fungicide sprays from petal fall onward in seasons with consistently wet summers — these prevent the surface fungal colonisation if applied preventively rather than curatively. Harvest at the correct time and do not leave ripe fruit on the tree through autumn wet weather.