There are thousands of leaf and twig galls that impact numerous types of trees and plants. There are more than 500 different galls that impact oak trees alone! In almost all cases, leaf, twig, or any type of gall on a tree or plant is of minimal concern. The variety of galls though is quite amazing and can be fun to identify while we are out in our urban forest exploring.
Woolly oak leaf gall can often be found in our area. It is caused by a gall wasp, sometimes called a gall fly. These are tiny wasps that don’t sting humans but lay their eggs on oak leaves. It isn’t entirely known what causes the gall, but it is a result of the plant tissue abnormally growing around egg or larvae, helping protect it as it grows. The end result is this cool looking fuzzy ball on your oak leaf.
Spindle gall on linden leaves are also commonly found in our area. The majority of linden trees will have this occurring somewhere throughout their crown. It is a result of mites feeding on the leaves and the plant tissue growing abnormally resulting in a spindle or nipple looking structure. The feeding these mites do has a minimal if any impact on the health of the tree and the gall itself is of no concern.
As you explore your urban forest, see what kind of galls you can find and never stop learning about the environment around us!