What is laying eggs on my bur oak and should I worry

Asked June 15, 2020, 8:38 PM EDT

For the past several years, my bur oak has been host to...something. At this time of year (mid-June), I see bright red balls on the leaves the size of grape seeds. As the weeks go by, I will begin seeing yellow puff balls on many of the leaves.
My concern is that it is either harmful to the tree or harmful to other nearby parts of my landscape. I have a lot of butterfly-friendly plants, such as milkweed and bee balm, near this tree so I want to know what is making a home in the bur oak.

Washtenaw County Michigan

3 Responses

Thank you for reaching out. Would it be possible for you to attach a couple photos/images below in this message? That would really help our experts provide a better answer/response.

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Thank you for the pictures.

These ‘eggs’ are galls and they do not affect the health of the tree, unless the tree is very young and its leaves are covered with galls. Oak tree leaves always have a few galls.

The missing leaf tissue is from insect feeding by something else, probably caterpillars. Unless you can find some caterpillars on the leaves, it isn’t possible to identify them.

Trees can lose 30 percent or so of their total leaf canopy and still survive. Keep your tree watered during hot dry weather, without flooding or drowning it.Too much water can be just as bad for a tree as too little. If in doubt, carefully dig down into the soil 6-9 inches and check soil moisture.

The yellowish slightly fuzzy galls may be young hedgehog galls. The red shiny galls are made by a different insect, although I couldn’t locate which one here in Michigan causes them. Each gall protects a tiny insect larva of a cynipid wasp, the main oak gall making insect family.

This response by MSU Entomologist Howard Russell explains more about oak leaf galls-

“Hedgehog galls, formed by the wasp Acraspis erinacei (Hymenoptera: Cynipidae).

Wherever oak trees grow, they are hosts to a group of tiny insects called gall makers. These insects cause abnormal growths or deformities, known as galls, of all manner of sizes, shapes and colors on leaves, twigs, bark, buds, flowers, acorns and even roots of the tree. The galls formed by Acraspis erinacei are just one of several hundred types of galls that form on oaks in the eastern US. The galls are far better known than the insects that cause them. Most of the oak gall makers are tiny wasps in Cynipidae family but there are a few that are caused by midges (Cecidomyiidae). Galls are caused by powerful chemicals or stimuli produced by the insect that interact with the tree hormones to produce the gall. The inner wall of the galls is rich in protein and other nutrients, which provides the developing larvae inside the gall with concentrated food supply. The galls also serve to protect the larvae, but not completely, from parasites and predators.

Each gall-maker induces the growth of its own distinctive gall that is unlike the galls formed by other species. Galls are so common on oaks that many people regard them as typical structures of the tree. Many gall makers have complicated life cycles with a phenomenon known as heterogamy or alternation of generations. The offspring of these gall makers produce galls that are quite different than their parents but that are identical to the galls produced by their grandparents. The alternating generations often produce galls on different parts of the oak tree. And, more amazingly, the alternating generations of wasps often differ in body structure to the extent that they appear to be two different species.

Oak leaf galls do not cause serious injury to the tree and I do not recommend attempting to control leaf gall makers with insecticides. Oak tree and gall makers have been getting along together for 1000’s of years. Insecticides should only be employed when the health of the tree is threatened.”

So, no, you have no need to worry about these interesting galls!