Sooty blotch and flyspeck are two different diseases caused by several fungi that commonly occur together on the same fruit. Neither disease actually damages the fruit. The discoloration is superficial and can commonly be wiped off.

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Causes:

  • Both diseases are caused by a complex of several different fungi.

  • The fungi only grows on the fruit surface

  • Rain and wind spread the spores onto developing fruit.

  • Most common during years with a cool, wet spring, followed by rains in late summer and low temperatures in early fall.

Symptoms:

Sooty Blotch:

  • Gray, green, brown, or black smudges on surface of apple

  • Smudges can be rubbed or washed off the fruit fairly easily

Fly Speck:

  • Clusters of tiny block dots on surface of apple; cannot be easily cleaned off fruit

How to Avoid:

  • Select an orchard site that always has full sunlight, good air circulation, and good soil (water) drainage.

  • Prune trees annually to maximize air circulation. Both diseases are most prevalent in the damp, low, shaded areas of the orchard.

  • Keep ground cover mowed short to decrease humidity and lessen fungi on fruit in the lower canopy.

  • Avoid planting blackberries and raspberries close to apple trees (brambles serve as an alternate host for the fungi that cause sooty blotch/flyspeck.

Treatment:

  • Successive spray solutions of coconut oil (made every ten days in late July, August and early September) may help abate serious problems with these fungi.

  • Remember that the disease is superficial on the skin of the fruit and seldom damages the flesh. Remove the fungus by washing/rubbing the fruit, or peeling.

  • Utilize potassium bicarbonate sprays

  • Is considered a cosmetic issue and spots can be wiped off or washed off. Fruit is still edible and marketable.

Sources: Ohio State University Extension, University of Minnesota Extension, UMass Extension Fruit Program, Patrick L. Byers, Horticulture Specialist, and Michael Phillips, “The Holistic Orchard.”