Although these two plant diseases are not caused by the same fungus, they are so commonly found in association that they are usually described together. Sooty blotch is caused by the fungus Gloeodes pomigena, and fly speck is caused by the fungus Schigothyrium perexiguum. These fungi spend the winter on the twigs of apples and many other woody plants. During mild, wet weather in spring, the fungi produce spores that are blown to and infect the developing apples. About a month after the initial infection, specks and blotches appear on the maturing fruit. Although these diseases are unsightly, they are external and do not generally affect the taste of the apples. Spores are not produced when temperatures rise above 85°F, so infection generally occurs during the spring and late summer or fall, but rarely in midsummer.
To prevent the possible infection of healthy fruit, spray with a fungicide containing captan. Infected apples are edible; rub them vigorously to remove the specks and blotches. Next spring, spray again with captan when the new growth appears.
Plant Care for Apple