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Red spikes growing on tree leaves #868769

Asked May 16, 2024, 4:50 PM EDT

Hello. I have a tree in my front yard, in southwest Minneapolis, that was slower than other trees on my property to leaf out this spring. Now, as the leaves are coming in, I noticed that they have these red spikes growing on them. A Google search tells me that they might be "leaf galls" but I wanted to get your opinion. What are these red spikes, and should I be worried about them? In case it's helpful to know, last year this tree had aphids. I sprayed down the tree really well with a hose, which seemed to remove most of the aphids for the rest of the season. Would these galls be related to the aphids, or something else? I do not notice any aphids on the leaves currently.

Hennepin County Minnesota

Expert Response

Thanks for your question.

You are correct in your conclusion that these are galls on the leaves of your linden tree. They are harmless and no treatment is needed. The following should provide you with some background information:

https://hortsense.cahnrs.wsu.edu/fact-sheet/lindentilia-leaf-galls/ - :~:text=These tiny, worm-like or,on the upper leaf surface.

I was asked a very similar question in July 2023. This is how I responded then:

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Thanks for the question.

There is no worry; there is nothing you should do; your linden is still healthy. What you are observing on the leaves are called galls. They have small mite larvae within them. Here’s the deal. Last year (2022) eriophyid mites (hard to identify the exact species) were present on your linden tree where they overwintered under pieces of bark or some other nook or cranny of the tree. This spring (2023) all these mites emerged from their hiding places and mated with one another. Eggs were laid on the emerging leaves of your linden and larvae quickly hatched. These larvae burrowed into the leaf tissue. The leaves responded by enclosing the larvae with a form of leaf cancerous growth. A type of defensive response. This led to the appearance of the bumps and nodules which you are seeing. The tree is not harmed in this process. Soon from each gall will emerge an adult mite. They are incredibly small so don’t expect to see them. These adults will spend the rest of 2023 and through the 2023-24 winter living on your tree. In spring 2024 the cycle begins all over again. See:

https://horticultureforhomegardeners.ca/2021/06/21/spindle-galls-unusual-growths-on-linden-leaves-caused-by-eriophyid-mites/

https://www.torontomastergardeners.ca/askagardener/weird-stuff-on-my-linden-tree-leaves/

https://extension.umn.edu/yard-and-garden-insects/insect-and-mite-galls

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These galls have nothing to do with the aphids you observed last season.Thanks for using our forum. Get back to us with any questions.

An Ask Extension Expert Replied May 16, 2024, 8:44 PM EDT
Thank you so much for your detailed response and expertise! I really appreciate it.

Simon


On Thu, May 16, 2024 at 7:45 PM Ask Extension <<personal data hidden>> wrote:
The Question Asker Replied May 17, 2024, 11:23 AM EDT

Glad to be able to help.

Thanks again for consulting us.

An Ask Extension Expert Replied May 17, 2024, 2:29 PM EDT

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