Apple Tree Diseases: Sooty Blotch And Fly Speck

Lauri Jean Crowe explains fly speck and sooty blotch - two apple tree diseases caused by microthyriella rubi and gloeodes pomigena. Learn about these apple tree diseases.

What is it?

Sooty blotch and fly speck are two plant diseases which occur in apple trees that are caused by two seperate fungi. Fly speck in apples is caused by the microthyriella rubi fungus while sooty botch is caused by the gloeodes pomigena. Both gleodes pomigena and microthyriella rubi are more often found together infecting apple trees rather than found individually which often causes apple growers to at first think they have one manifestation of the same plant disease when they actually have two overlapping disease processes occurring in their apples.

What does it look like?

Sooty blotch, caused by gloeodes pomigenia fungus usually manifests as the appearance of brown or olive green colored spots. These spots are smudgy looking in appearance and will manifest anywhere on the surface of the apple fruit. Fly speck caused by microthyriella rubi fungus usually appears as anywhere from ten to thirty clusters of raised spots which can appear anywhere on the surface of the apple fruit. The variable clusters of raised spots are black and tends to be very shiny and reflective compared to the rest of the surface of the apple fruit. Although both gloeodes pomigenia and microthyriella rubi fungi show damage on the apple fruit, they actually infect the body of the apple tree often over wintering on the twigs and branches of apple trees.

How does it manifest?

Both fly speck and sooty blotch over winter on apple tree twigs, braches and mummies, or fallen fruits that have mummified. The fungi remains dormant throughout the winter until springtime when wet weather erupts in conjunction with mild temperatures. These climactic changes allow for the production of and spread of spores of the microthyriella rubi and gloeodes pomigenia fungi. 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.

What can you do about it?

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.

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