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I have an older crab apple tree that is focal point of my small yard. About 3 years ago the leaves became infected with powdery mildew. I have been told to not do anything with this, as it will eventually go away and the tree will fine - but over the years it has gotten much worse each spring. There are only about 60% of the leaves that are starting to look healthy by mid-June. Over all, the leaves are withered and this year we have very few blossoms. Another problem: The tree also has four large limbs that come out of the trunk. I noticed that there seemed to be wood pulp inside a place where a branch was cut off years ago. I scooped out the pulp and found that some bug or other creature has created a cavity that goes 6” into the 10-12” diameter limb and a large man’s fist could easily fit into the hole that has been created. While inspecting the hole I discovered a ¼” or so hole in the very back of the cavity, but no sign of the culprit. The limb seems to be doing fine, as the leaves on the branches from this limb are in no better or worse shape than the rest of the tree. I had my tree pruned by a highly recommended person this spring, in hopes that this would help with my powdery mildew problem. I love my tree, what should I do next about my perpetual powdery mildew problem and the unknown culprit who is dinning on my tree limb?

Answer(s)

A

Years when we receive a lot of rain and have cooler temperature makes powdery mildew harder to control.  While the weather can't be controlled some there are some things that you can do to help your tree. If the canopy of the tree is dense thin out some of the branches to help increase air circulation.  If your tree is watered by sprinklers, water earlier in the day so the leaves can dry before nightfall.  There are also commercially available fungicides that can be used to treat powdery mildew.  If you do choose to use a fungicide make sure to read and follow all of the instructions on the label carefully.  Below is a link about Apple Powdery Mildew that has more information. 

http://extension.usu.edu/files/publications/factsheet/apple-pm00.pdf

As for insect damage you would need to bring a sample in to our office for identification.  If possible a sample of the insect would be best.  If you are unable to find the insect you could bring in a sample of the damaged portion of the tree.   We are located at 2001 S. State Street S1200. 

Posted on 29 Jun 2009

Heidi Wayman
Horticulture Intern, Salt Lake County

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