Question
I too have an infestation of hershey kiss galls on my Quercus lobata that I planted in my back yard about 20 years ago. The tree is now about 30' tall and every year there are more and more hershey kiss galls. There must be over 1,000,000 of these on the bottom of the leaves and they are starting to get annoying. There are about 10 on the bottom of every leaf in the tree. I have been hesitant to do anything about them because I really don't like using pesticides in my yard. It seems the native birds do a pretty good job at keeping most insects at bay except the hershey kiss gall. So this spring I am planning on using a systemic on the tree to try to slow the Hershey kiss gall down. But I really don't now if this is the best way to stop them, or when is the best time to apply the systemic. Any ideas here would be appreciated.

Answer
Gall insects are difficult to control because usually controls are aimed at the adult insects. Timing would be a problem since the adults are not around long--usually just during egg laying. Spray insecticides are aimed at adults and would do little to control the larvae in the galls. The gall insets lay their eggs on the leaf surface and secrete a chemical that cause the cells on the leaf surface to expand and grow over the eggs forming the gall. The young then feed inside the gall until grown.
I would try a systemic insecticide that is applied to the soil around the tree and the roots take it to the leaves and when the young feed they are killed. You still will get the galls this year but the population will greatly be reduced next year. The best time to apply this type treatment is in the spring as the leaves are budding out. The roots are pulling more liquid up this time of the year. The insecticide I recommend is Bayer Advanced Tree and Shrub Insect Control. You should be able to get it at a local nursery/garden type store. Here is a web link to more information on this insecticide.
http://www.bayeradvanced.com/product/Tree-Shrub-Insect-Control/concentrate.html