What can be done for a birch that has leaves with bumps and turning black?

September 14, 2022 Ask the Expert, Managing Insect, Diseases, and Animal Pests

Question:

My question is about a Fox Valley Dwarf River Birch.   In 2021, we noticed bumps on the leaves. We went to nursery and it was suggested we use a systemic product which we did. Bumps remained but the tree continued to thrive. This year, the bumps came back immediately. We again asked from the nursery what to do. We were told once the bumps appeared, there was nothing we could do and it would not hurt the tree.  Again, the tree grew and thrived.
Now, tree is loaded with the bumps and some turning black. What to do?

Answer:

Lynne M. Holland, Horticulture and Social Media Professional

That certainly sounds frustrating and it seems to be progressing.  Without a picture it is hard to diagnose, however please look at the picture on this page and let me know if this is what you are seeing on your tree.  If it is then what you have are leaf galls.  There is an expert explanation on that page is this is what you have.

It is true that once you see the bumps there is little you can do for the leaves that season.  It is also true that the galls do not hurt the tree, they are the tree’s defense against an invader.  Identification of that invader should be done by an arborist in the spring and then perhaps a spray or dormant oil can be used but there are risks with any application of anything to a tree.

The galls tuning black indicate that the invader may be an aphid that produces “honey do” which then attracts a fungus or bacteria. That would be considered a secondary infection.  But again without a picture that is just a guess.

I suggest reaching out to the nursery one more time and bring in a sample branch (or part of a branch) and ask them for an expert to determine what the invader is that is causing the tree to produce galls.  Then see if they recommend an arborist for preventative application next spring.  This season clean up all affected leaves and remove them from the area.  Pay close attention to the bark and branches of the tree in the early spring to see if there is an adult insect laying eggs on the budding leaves.