Early Spring 2012, Oak trees all along the coastal areas of Falmouth, Yarmouthport and Brewster began showing very serious signs of die-back and stress. It was not very clear at first what
was going on with these distressed trees. Perhaps these trees were suffering from the salty blasts of wind they received from Hurricane Irene the previous year. After all, it didn’t rain again after that storm for quite a few weeks. And then we had such a mild winter here on Cape Cod. Or maybe the successive years of defoliation from the Winter Moth “plague” we’ve been experiencing here have taken their toll on these trees. Many theories as to why these trees all seemed to be suffering so suddenly and so drastically, but it wasn’t until Robert Childs, Plant, Soil and Insect Sciences with the UMass Amherst Landscape, Nursery and Urban Forestry Program, announced the discovery of a very small insect that the answer became clear.
Cynipid Gall Wasp otherwise known as the Crypt Gall Wasp (Bassettia ceropteroides) was confirmed to be the culprit of all of this Oak die back. The chief symptoms of infection are the clearly visible lack of leaves, early flagging (or leaves losing green color), and swollen twigs. Closer examination of the swollen twigs reveal small exit hole created by the adult wasps emerging. The loss of foliage can be up to 90% in some trees.
There are over 700 species of gall wasps in North America that form galls on Oak, but none seem to be so destructive as this new comer to Cape Cod. Very little is known about the habits and life cycle of this small pest. It is thought that female wasps lay eggs in early spring before foliage is completely unfolded, and the eggs hatch out larvae that feed into the twig as the tree grows. This feeding forms an enclosed chamber within the twig and the saliva of the larva actually produces a genetic mutation in the tree. This is how the swollen gall is formed. The larvae go on to feed on nutrients within this enclosed chamber. The larvae mature into an adult
female wasp, which then chews thru the twig to emerge on the surface. The damage that the larva inflicts on the vascular system of the trees twigs is what cuases the loss of leaves and weakened canopy. Read full fact sheet about Bassettia ceropteroides here.
Trees that have experienced previous stress seem more likely to suffer die-back from the Gall Wasp. Therefor steps should be taken to increase the health of susceptible Oak trees, particularly, along the coastline. Avoid drought stress and defoliation from Winter Moth feeding. Also improving soil fertility may help to alleviate stress on affected or susceptible trees. There are treatment strategies that may help to protect your trees from infestation, but as we are still learning about the life cycle of this insect, specific controls are still being developed.
Contact Forest Keepers to help manage the health of your shade trees this coming season as this outbreak continues to develop. We will keep you updated as more is learned about this destructive pest.