Expert: Jim Hyland - 9/9/2006

Question
I have two live oaks in my yard and have found galls in varying sizes on both (1/4" up to 2" dia.)  I cut them off as soon as I see them, but wonder if there's a better way to deal with them.  In the past I've used a commercial liquid that you feed the tree which supposedly stops parasites.  After two years of this treatment I see no relief.  Also on these trees I find little 'balls' on the underside of the leaves.  They start out pale yellow and very tiny; they grow to about 1/4" in size and turn almost black in color.  Are these related to the galls or do I have two problems?  Thanks.  

Answer
They are all galls caused by an insect (small wasp) The wasp lays its eggs on the surface of the leaf or twig and secretes a chemical that causes the tissue of the leaf or twig to swell and cover the egg. the eg hatches and moves on. The galls themselves will not harm the overall health of the tree although they can look bad. Leaf galls may cause the leaves to drop permaturely. There are many types of these wasps some attack the twigs and others the leaves. Control is not usually needed and has to be timed with the wasp presence and not the galls themselves. Here are a web links to a couple of sites on gall wasp that discuss the wasps and control measures.
http://entomology.unl.edu/ornamentals/pestprofiles/gallwasps.htm
http://www.ces.ncsu.edu/depts/ent/notes/O&T/trees/note05/note05.html