Are these two "growths" on my tree a gall?

Asked August 28, 2020, 11:43 AM EDT

These two (each about the size of a small lime) "growths" have appeared near the top of a vine maple in my yard in Portland. I'm guessing they're galls, but I haven't been able to verify. Wondering if you happen to know what they are and if I should do anything to protect the tree or just let nature run its course.

Multnomah County Oregon

2 Responses

Galls that form on leaves are less harmful to the tree than those that form on twigs. Plant galls are formed in response to an interaction with insects, (mites, nematodes, viruses or fungi) and the plant tissues. Egg-laying, salivary secretions or mechanical injury initiate production of localized plant hormones which cause accelerated growth (larger plant cells or increased number of cells) of the growing tissue. The plant tissue grows around the insect or mite protecting it from weather and natural enemies. Galls can form in the developing tissues of any plant structure including leaves, buds, stems, flowers, shoots or roots. Generally, damage is not significant to the plant, but may be considered unsightly by homeowners, or may be excessive in some years. Occasionally, infestations flare up to significant numbers and the plant will form abscission cells which cause infested leaves to drop from the host along with the insects or mites inside. Insect galls rarely kill plants and they are heavily parasitized in most years. Low numbers are not harmful to trees.

Most galls can be viewed as an interesting partnership between plant and gall maker. Rarely are they numerous enough to warrant control. Most homeowners find they can tolerate gall insects once they know the plant is not going to die. Prune out or remove galls on infested twigs, buds or leaves if they are found to be objectionable.

Hope this helps!

Thank you for the response, and I hope you're safe from wildfires.