Our Haralson apple tree has a white fungus growing on its south side. This is...

Asked September 9, 2013, 8:55 PM EDT

Our Haralson apple tree has a white fungus growing on its south side. This is an off year for its harvest. No apples made it through the summer, though there were a few that started growing before molding and falling off. The bark on the trunk is splitting a bit, likely caused by the sun above the snow line causing cracking. I've heard from another northern apple grower that a bit of white paint can help reflect sunlight. What is this and how can we help our tree? I'm really looking forward to cider, and would be sad to see it die.

Polk County Minnesota

1 Response

Although we can't be certain without seeing the tree, it's possible the mold on the trunk is growing on honeydew secreted by sucking insects such as scale or aphids. The generic name for such growth is "sooty mold." The trunk of the tree appears to have been blackened by sooty mold with white mold also present.

Go to the following websites to learn more about sooty mold and how to control the insects that deposit the honeydew.

http://www.extension.umn.edu/yardandgarden/ygbriefs/p440sootymold.html

http://www1.extension.umn.edu/garden/diagnose/plant/deciduous/linden/branchescolor.html (Scroll to 4th photo)

Sooty Mold on Trees and Shrubs
http://ohioline.osu.edu/hyg-fact/3000/3046.html

Go here to learn about sunscald and ways to control it:

Winter Injury on Trees
http://www.extension.umn.edu/yardandgarden/ygbriefs/P466winterinjury.html