What's growing in my tree roots?

April 24, 2017 11:13 AM

While doing some yard work, I found that my tree (oak) had some shallow roots that were coming out of the ground. While pruning and digging around for a bit, I found there were some strange hollow things in the root system that I'm having a hard time identifying.

Pictures of the... whatever it is... are here. These things appear to have had insects in them, as I found larvae in one of them as I broke it apart.

So, now I'm worried I have a problem. Unfortunately, I don't appear to have the language required to get google to tell me what this is... Searching for permutations of "tree root" +"larva" + "hollow thing?" returns nothing that looks like this thing.

Does anyone know what this is, and whether I should be worried about it? Is this going to harm the tree? Can I get rid of them if so? What keywords could I use to find out what this stuff is?

Thanks!

posted by bessel functions seem unnecessarily complicated to Home & Garden (6 answers total)

Those look to be root nodules.

There are many plants which use root nodules to store nitrogen.

I don't know if oak trees do this.
posted by tomierna at 11:25 AM on April 24, 2017

Some sort of gall I think.
posted by exogenous at 11:25 AM on April 24, 2017

Yes, they seem to be galls. Galls can be caused by fungi, bacteria, or nematodes. Or they can be caused by insects. Since you found larvae in one and some of them have what appear to be holes where adult insects emerged, these seem to have been caused by insects. Many galls are caused by wasps but other insects like flies can also be responsible. The fact that your tree is an oak is important. Many galls are found only on a particular type of plant. I would start by searching something like "oak root galls." If you know what species of oak you have, you could include that in your query.
posted by Redstart at 11:40 AM on April 24, 2017 [2 favorites]

Agree on nitrogen fixing root nodules. Do you have lupine, peas, sweet ferns--anything else around the tree?
posted by A Terrible Llama at 1:14 PM on April 24, 2017

Or maybe not. The appearance of the galls on the roots can be confused with nitrogen-fixing nodules common in the legume family. However it is easy to distinguish between them, as the nitrogen nodules can be easily rubbed off while the nematode galls cannot be removed.
posted by A Terrible Llama at 1:17 PM on April 24, 2017

Oak (genus Quercus) trees do not form nitrogen fixing relationships with bacteria in root nodules.
posted by congen at 1:42 PM on April 24, 2017