Maple scorch, wilting and dieback remain a mystery

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.

We have recently confirmed that this season’s unusual and widespread maple problems in Michigan have also appeared widespread in New Jersey. Samples of leaves submitted for testing to MSU and Rutgers University have shown interveinal necrosis or cross-vein and marginal necrosis on the leaves which are typical symptoms of leaf scorch. However, several reports of terminal branch wilting and dieback have lead to confusion about the etiology of this disease or disorder. A number of samples have now been tested for the presence of the bacterial pathogen, Xylella fastidiosa, which causes bacterial leaf scorch [BLS] and all have been negative. These samples included Norway, Sugar, and Red maples, plus variegated and ‘Red sunset’ cultivars. The negative test results were expected because the sudden and widespread occurrence of the scorched and wilting terminal leaves are more characteristic of an abiotic or physiological disorder brought on by unusual climatic conditions, as earlier suggested by Dr. Dave Smitley. The reports from New Jersey also are suggestive of a climate-related disorder.

Where do we go from here in improving our understanding and the accuracy of our diagnoses?

We hope to put a special effort in confirming or denying whether verticillium wilt is a contributor in some portion of the damaged trees. One reason for this approach is based on the reports and samples of currently dying branches, or branches that were reported as dead only this season. An abiotic scorch is unlikely to lead to branch wilting and dieback, other than some wilting of the most succulent shoots at the very terminus of the branches. Additionally, we need some careful observation on whether the “dead branches” are actually setting new buds and thus likely to recover fully next year. To continue this diagnosis, we need your help.

Please send in samples of the maple scorch, wilting and dieback that include the leaves attached to an affected branch (say five to 10 inches long). We will help in isolations aimed at recovering Verticillium from the vascular systems. Samples can be sent to:

Gerry Adams Lab
268 Plant Biology
Michigan State University
East Lansing, MI 48824

What can you do now?

We can predict that most of these maples will return to a healthy appearance next season if no branches are currently wilting or recently dead. Such information may moderate the homeowners and landscapers immediate concerns. For those experiencing recent branch dieback and wilting, a recommendation of pruning aimed at balancing the foliage to the apparently inadequate root absorption, and removing unsightly dead branches, could not hurt. Such treatment is likely to help the trees recover more quickly in health and esthetic appearance. Currently, we assume that weather conditions that favored the occurrence of this malady will be as rare in future years as our memory of past years and maple disorders. However, if the climate is changing, then only future observations will be informative for predicting correlations of climate and the maple problem.

Dr. Adams's work is funded in part by MSU's AgBioResearch.

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