Q: My son has two beautiful oak trees (one in the front yard and one in the backyard) probably 25 years old. Both have what I believe are ‘gall’ balls. Both are loaded with them. Is there any way to get rid of them? Last year they were mostly smooth and not that hard to pick up when he was mowing. This year they have what are like thorns. He doesn’t want to cut them down as they shade his house really well, but these are horrible.
A. J. of Belleville
A: You are describing actually two different gall forming insects. The smooth one is commonly called the oak apple gall (Amphibolips confluenta), as it grows to the size of a medium apple, and when it first forms has a green skin. Later, this skin turns papery tan. When you cut it open, this gall contains a mass of fibers that has small areas that look like seeds, but are actually the larvae in a central cell. This gall causes very little damage to the oak tree. You can collect them easily when they fall, as you stated, and burn the galls to help eradicate them. If you look closely, these galls actually start on a midrib on the oak leaf.
The other spiny or thorny gall is a different story. It is actually called the horned oak gall (Callirhytis cornigera) and is found mainly on pin oak trees and some other oaks. This gall is caused by small wasps that lay eggs on young developing oak leaves in early spring (usually in May, but this can be earlier or later depending on spring weather temperatures). These form a small leaf vein fuzzy galls. You can control by spraying the developing leaves with Sevin insecticide.
Males and females develop from these fuzzy galls. After mating, the small female wasps lay eggs on the small twigs of the oak tree. These eggs form spiny galls and grow over a two-year period and usually kill the branches outward. These branches fall off the tree over time. Cleaning up the leaves and small branches that drop off helps break the life cycle. Use thicker gloves when handling the spiny galls to prevent injury. You can either burn the branches, if allowed in your area, or bag them in a plastic bag and leave these spiny galls in the bright sun to kill them.
Also, in some years when the galls, especially of the horned oak gall, are heavy, some people have been bothered by ‘itch mite,’ which bites and causes itches similar to a chigger bite. This is actually small wasps from the spiny gall.
There has been some research to develop resistant pin oak trees, as there are some non-infected pin oak trees growing now in the same area of infected pin oak trees. But over time, it has not been successful.
Charles Giedeman is a local contributing writer. Send your gardening questions to Lifestyle Department, Belleville News-Democrat, P.O. Box 427, 120 S. Illinois St., Belleville, IL 62222-0427, or email them to firstname.lastname@example.org.
Things to do this week
- Shade trees can be safely pruned now.
- If you notice wilting on trees and shrubs, apply one inch of water into the soil per week.
- Do not prune any spring flowering shrubs after July, as you will pruning off next spring’s flowering buds.
- Divide and transplant oriental poppies after they have finished blooming.
- Water roses before 10 a.m. Try not to spray the leaves with water as this could cause fungal diseases.
- Check you evergreen shrubs and trees for the need for water especially with this dry weather.