Some arborists reported an unusual number of Norway and sugar maples with a few wilting branches or
July 24, 2009 - Author: Dave Smitley, Michigan State University Extension, 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.
Some arborists reported an unusual number of Norway and sugar maples with a few wilting branches or isolated branch dieback in June and early July this year. Many trees have been examined and quite a few samples sent to Diagnostic Services at MSU, examined by myself and Gerry Adams.
Some samples examined had branch dieback, most likely from 2008, with branches infested with ambrosia beetles (similar to a bark beetle). See Howard Russell’s article. Two species of ambrosia beetles, the black stem borer, Xylosandrus germanus and the European shot-hole borer Anisandrus (=Xyleborus) dispar have been recovered from these samples. So far these ambrosia beetles appear to have only been found on branches that appeared to have wilted or scorched last year. This is typical of bark beetles and ambrosia beetles being a secondary pest of compromised branches or trees.
So far, we suspect there are multiple causes of the branch scorching, wilting and dieback symptoms observed this spring and early summer. Several arborists and extension educators have commented that it is relatively easy to find a little branch dieback on maple tree street trees with restricted root systems, poor soil, drought stress, or girdling roots. We hope to receive more samples from maple trees that are examined for Verticillium wilt by scraping bark from the base of wilted branches and trace back to larger branches that feed them until some vascular discoloratioin is found, and also from trees examined for bark beetle, ambrosia beetle and borers. As more information and samples come in, we will keep you informed of the results of the diagnoses.