This time of year, it is not uncommon to see the valley oak trees
(Quercus lobata) with their leaves yellowed and splotchy with numerous small seed like balls on the underside. These are called Jumping oak galls and they are made by a small Cynipid wasp larva (
Neuropterus saltatorius) that is developing inside the gall. Don’t worry-the wasp doesn’t sting humans. In fact, you would be lucky to actually see the critter. While the galls do cause some defoliation, they are not particularly harmful to the trees. They may cause some serious leaf loss in some years and this year seems to be one of those years. The adult female wasp, in order to be able to create a gall that contain an egg, must sting the leaf at precisely the right time. If the leaves are too fully expanded and hardened off, the galls will not form. That is why you might see one tree with millions of these galls and yet the one nearby might not have any. Their foliation times may be somewhat different. There are many types of oak galls including yhose that look like chocolate kisses and some that look like apples,
and still others that look like horned or fuzzy balls. We do not normally recommend any type of control of these insects. However, some research indicates that if one leaves the infested leaves on the ground, the parasites of these little wasps are not raked away and it may moderate the population over time. As well, there is more “mulch” on the ground around the trees, which is a good thing.
One of the fun things to do with the galls as they are beginning to fall off the tree is to just bring them into the house. As the galls warm, they begin to jump and wiggle around and make a snap crackle and pop noise….
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