Taphrina gall on River Birch? #659963

Asked July 05, 2020, 1:31 PM EDT

Every year I have what looks like a gall that forms on the leaves of my River Birch 'Heritage'. It does not affect the tree leafing out and growing. I clean up all the leaf debris & water the tree at the base only. Is it a Taphrina species or an insect gall?

Sussex County Delaware

Expert Response

That looks like an insect gall. It won't harm the tree you just need to clean up the fallen leaves as you are doing.  In order to control it next year, you would need to ID the insect and spray in early spring targeting the particular insect.  An insecticide will kill beneficial insects as well, though, so since it is not harming the tree, I do not recommend controlling this problem.

Image of galls on leaves

Susan Barton, PhD, SITES AP Replied July 06, 2020, 9:19 AM EDT
Thank you, Do you think if I place some leaves on a branch in a closed terrarium I would be able to find out what insect it is.  I have searched for 2 years and cannot find an insect. i assume the crawler stage would be very tiny?
The Question Asker Replied July 06, 2020, 12:35 PM EDT
I asked our IPM specialist and this is his reply:

I would say it most likely is an insect. It is also an insect that does not warrant treatment. Treatments for gall forming arthropods (insects in particular) require application during early leaf formation (bud break usually) or shortly thereafter. If it is a contact insecticide they are usually broad spectrum and negatively impact the beneficial arthropod community. Work with other gall forming insects has found that treatments with these broad spectrum insecticides provide no more control than the natural enemies provide on their own (i.e., no net benefit, and most likely loss because the natural enemies are not around for other possible pests it may target). Systemic products may provide some control, but I haven't heard anyone using them for this purpose and it may not be on the insecticide label. Additionally, the systemic products are usually organophosphates (older compounds and issues associated with those) or neonicotinoids (possible impacts on pollinators if applied near flowering plants). Since the galls really do not impact tree health, it really is not worth the time, effort, or money needed for treating the tree for this pest. A possible option (although not likely very effective) would be to rake leaves up from underneath the tree in the fall. I don't think this will have much impact because I think that when the arthropod matures it leaves the gall and lays eggs for next year on those buds.

Susan Barton, PhD, SITES AP Replied July 08, 2020, 10:50 AM EDT

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