Saturday, September 19, 2009

You Have a Lot of Gall! Ask the Snarky Farmer...

Dear Farmer Fred,

Can you identify the pink and little brown balls growing now on our oak tree? I don't remember seeing these before.
Is it some kind of parasite? If so, what should we do? Thank you. We enjoy your weekly show very much.

Margaret of Shingle Springs (CA)

Yep, it's gall season in the California foothills! Galls are interesting creations of several variety of (usually harmless) wasps. No action is necessary on your part, except to enjoy the show.

The Integrated Pest Management Project at UC Davis says this about galls: "Most galls are caused by cynipid wasps and gall midge flies. The adult gall wasp is a small, stout, shiny insect with very few wing veins and a purple or black body. Adult gall midges are tiny, delicate flies, often with long, slender antennae. Galls are distorted, sometimes colorful swellings in plant tissue caused by the secretions of certain plant-feeding insects and mites. These unusual growths may be found on leaves, flowers, twigs, or branches. Most galls are not known to harm trees. Prune and dispose of galls if they are annoying. This may provide control of some species if pruning is done when the immatures are in plant tissue and before the adults begin to emerge."

State entomologist Baldo Villegas chimes in:
"Your picture of a blue oak tree have several types of oak galls made by several species of small, non-stinging wasps in the wasp family "Cynipidae". As an entomologist, we refer to the members of this family as "cynipid wasps". They are unique among the wasps in that they lay their eggs on plant tissue resulting in a distinctive plant gall encasing the egg/larva. Each cynipid wasp species make different and distinctive galls and one can identify them based on the gall type. Obviously, your blue oak sample had several types of galls and therefore several species of wasps. There is not much you can do to control these gall wasps. They are native species that co-evolved with the blue oaks in the area. The wasps are not killing the trees and they also don't appear to weaken them; so, my recommendation is to just let them be.

1) The most obvious are the "echinid galls" produced by the wasp "Dryophanta echina".  These galls vary from pink to bright red and have the spiny galls.

2) The second gall that you asked for was for the small brown galls that look like little brown balls? These are probably "jumping oak galls" caused by the wasp "Neuroterus saltatorius.

Thanks, Baldo!

Other interesting oak galls:

And here's more fun with jumping oak galls.


  1. Our big, beautiful valley oak appears to be dead. The leaves turned brown in about a week and are still hanging on the tree. Almost every leaf is covered with pink, spiney balls, which look like the picture at the top of this article. I'm being told to do nothing and wait until next spring, it might not be dead. However, small branches appear to be brittle. What happened? And will this effect our other oaks?

  2. That was good advice, wait and see. The galls should not be adversely effecting your oak tree. Was there a radical change in the watering in that area this year? That may have a bearing on the problem. Also, check this link for other oak problems, especially the section labeled "environmental disorders":