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Friday - August 15, 2008

From: Coon Rapids, MN
Region: Midwest
Topic: Diseases and Disorders, Soils, Trees
Title: Leaf drop from maple tree in Minnesota
Answered by: Barbara Medford

QUESTION:

I have about a 30 ft maple tree in my yard, last fall I trimmed it pretty good because the branches were getting low where you could not walk under it or get grass to grow. This is the 2nd time in about 6 years I did this. It filled out nice this spring and looked normal and healthy, but the last couple days green leaves started falling off, not a lot but enough to notice with more everyday. Is this tree dying, if so is there anything I can do to save it?? I live in Minnesota. Thanks

ANSWER:

Out of a list of 18 members of the genus Acer, there are 7 that are listed as growing in Minnesota, so we think it's safe to assume that you have planted a tree that is appropriate to your area. We have selected Acer rubrum (red maple) as the one to research, assuming that most maples native to Minnesota would have pretty much the same characteristics and potential problems.

One of the possibilities we found was that the maple family is prone to Verticillium Wilt. This University of Minnesota Extension website on Verticillium Wilt of Trees and Shrubs has an extensive discussion, with pictures, of the symptoms and possible treatments of this disease. It was noted that Verticillium Wilt is most apt to appear in July and August. The Acer can tolerate some periodic flooding, but, especially under other urban stress conditions, the flooding will enhance the chances of contracting Verticillium Wilt.

The maple tree is considered inappropriate as a street tree; it does not respond well to urban stress, can get quite large, and has surface roots which will interfere with paving, sidewalks and lawns. Two other problems that may be causing your leaf drop are leaf scorch and leaf chlorosis. If your maple is growing in an alkaline soil, the roots may be unable to access the magnesium in the soil, and thus become nitrogen deficient. This will cause yellowing of leaves, and may stunt the growth of the tree. Treatment with nitrogen or amending the soil around the roots with organic materials such as shredded bark can help to alleviate those problems. Leaf scorch is browning of the leaf margins. Scorch symptoms are often more severe on outer, more exposed leaves. Often, leaves on one side of the plant may be affected, while the rest of the plant is normal. This may occur on a side of the tree where the roots are limited by paving, etc. Leaf scorch is caused by failure of the tree to provide enough water to the leaves at a critical time, usually in July or August.

We have given you several possibilities for the problems your tree is having; at least two of them frequently occur in July and August. However, we don't know what your soil is-alkaline or acidic, or if there is Verticillium Wilt present in the area. Your best source of information would be the Anoka County Extension office, associated with the University of Minnesota. If there are more problems similar to yours in the area, they will know about it, and can help you with possible treatment.