The fungi is carried by wind or water and splashes or floats onto the surface of previously healthy apple fruits. Spore production stops once temperatures have reached the mid-eighties so most infections of microthyriella rubi and gloeodes pomigenia occur in spring or late summer. The fungal spores of sooty blotch and fly speck infect the developing apple fruits and the actual signs of damage such as the smudgy blotches and black specks do not typically show up on the apple fruits until approximately one month after the initial fungal infection from spores. Typically these plant diseases remain external to the surface of the apple fruits which can make the apples appear unsightly. However, sooty blotch and fly speck do not alter the taste of the apple fruits, and do not make them inedible.
Infected apples are edible, despite being unsightly.
To remove the smudges, and spots, rub the apple fruits vigorously either up and down on a cloth or in a circular motion. You will need to apply some pressure, but not too much or you will just end up bruising the tender apple fruits on the inside. Once you see the appearance of the characteristic specks and spots you can spray the fruit as it develops with a fungicide. Your local cooperative extension office can tell you which fungicide works best for apple trees infected with gloeodes pomigenia and microthyriella rubi in your area. If these two plant diseases are problematic in your geographical region you can also spray the apple trees as soon as new fruit appears on the apple trees each spring.