Knowledgebase

Trim an Elm in August #878235

Asked July 22, 2024, 11:37 AM EDT

Hello Master Gardener: We have an ~ 100 year old elm tree in our yard. We treat the tree with fungicide injections every two years. Recently an employee of the treatment service trimmed several dead branches and suggested that the tree now has Dutch Elm disease (he removed bark from a trimmed branch and showed us brown streaking). He suggested that the best course of action is to immediately remove one of the four main branches of the tree to stop the infection. However, the tree trimming service we use said that removing a branch this time of year (late July or August), could invite even more rapid spread of Dutch Elm. My question: Should we remove the main branch now (in early August), or wait until October / November when the beetle is dormant? Thank you.

Hennepin County Minnesota

Expert Response

Thank you for writing.
The instructions on this are not clear. Dead branches or dying branches with intact bark or structurally unsound branches may be taken down promptly.
https://www.alberta.ca/dutch-elm-disease-prevention-what-you-can-do
https://extension.umn.edu/plant-diseases/dutch-elm-disease
Elm disease infected branches should be completely removed anytime if the signs of infection are is at least 5 feet from the trunk.
All such wood from trees with Dutch Elm Disease should be disposed of as if infected with the disease.
Without seeing all of the base of this tree, it appears to have three trunks at highly acute angle. Such trees are at increased risk of catastrophic failure if disease gets to the core. I suggest that you urgently address this matter with your arborist.

Steve Miles, Hennepin County MN (I am a human being, neither a bot nor AI). I am happy to receive follow-up questions if my responses are incomplete or unclear. This is the University of MN' garden soil testing service. https://soiltest.cfans.umn.edu/testing-services/lawn-garden This is guidance on how to find a tree expert. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional The Minnesota Landscape Arboretum is a wonderful place to see and learn about plants that grow in Minnesota. https://mngardens.horticulture.umn.edu/minnesota-landscape-arboretum Replied July 22, 2024, 11:55 AM EDT

Hi Steve:

Thank you for your response. It helps.

You seem to be suggesting that the risk of trimming infected branches (5 feet from the last sign of streaking) in August is LOWER (in your opinion) than the risk associated with waiting until October. Correct?

Note: We realize that the ultimate decision is ours.

Ed Parker

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The Question Asker Replied July 22, 2024, 12:28 PM EDT

Thank you for writing back.
I am conveying the finding on proper management of a governmental and university authorities. I am a messenger in the sense that I found those relevant authorities.
In my opinion and given an incomplete photo of the base of the tree, the primary danger here may be catastrophic splitting of the three trunks of this tree. Arborists have specialized tools for assessing this risk. I would appreciate hearing your arborists opinion. Note: you should rely on the view of an ISA certified arborist. https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional

Hello Steve:

Thank you for your response. We will find an ISA-Certified arborist for another opinion and forward you the information when we have it.