Update on the reports of upper branch dieback in Norway and sugar maples around Ann Arbor
September 18, 2009 - Author: Dave Smitley, Michigan State University, Department of Entomology
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
In late May and June of this year several arborists from Ann Arbor and
the western suburbs of Detroit reported seeing an usual number of Norway
and sugar maples with some upper branches that were dead, wilting or
had stunted leaves. The affected branches were usually scattered about
the crown, among other relatively healthy branches. The branch dieback
was usually observed on stressed street trees that were either old,
growing in poor soil, or restricted by pavement. Symptoms appeared
before water stress became an issue this year. After a Landscape Alert article
on this problem, people from other parts of the state reported some
similar symptoms, including Paul Schwarz, head arborist for MSU grounds.
When Bert Cregg and I looked at the maples on campus with Paul Schwarz we noticed that the worst-looking trees tended to be on poor sites or to have some lower trunk damage. In some cases, we found signs of borer activity on the trunk or at the base of some branches. When we followed those branches up they were the same ones with dieback symptoms. We will be removing one or more of these trees to scrape branches and look for borers and fungal diseases.When Bert Cregg and I looked at the maples on campus with Paul Schwarz, we noticed that the worst-looking trees tended to be on poor sites or to have some lower trunk damage, in some cases, apparently followed by a borer infestation. We will be removing one or more of these trees to scrape branches and look for borers and fungal diseases.
At this point, we don’t have any common cause for the scattered branch dieback observed on Norway and sugar maples this spring and summer. Some of the things to consider are drought stress, girdling roots, basal wounding, and trunk cracking, all of which can make trees more susceptible to attack from borers. Verticillium wilt is another common problem on maple trees, but the symptoms are not usually restricted to individual branches, and once Verticillium causes branch wilting, the entire tree often dies within a year or two.
We are still investigating this problem, and we would appreciate any observations or thoughts that you have that will help us. Email me at email@example.com. Meanwhile, you may want to check the base of branches showing dieback (or the trunks of smaller trees, under 8” dbh), and look for sunken areas of bark, cracking, swelling, and emergence holes. If these symptoms are present, scrape the bark and look for borers.
Gerry Adams would also like to know if you see any Armillaria root rot on Norway and sugar maples with branch dieback. Armillaria root rot has killed some large old trees in other parts of the state, following multiple years of drought stress. However, these were not necessarily maple trees, and maple trees are not usually considered to be one of the more susceptible tree types. Contact him at firstname.lastname@example.org.
If we learn any more about this problem during the off-season, we will provide an update via the Landscape Alert on-line and in the first print version this spring. Thanks for sharing your observations.