Cape Cod Insect Alert

The Cynipid Gall Wasp: What it is, what to look for, and what to do

The cynipid gall wasp, identified in Cape Cod by Russ Norton, Horticultural Specialist at Cape Cod Cooperative Extension, has become a dangerous threat to the beautiful red and black oak trees common to the area.

Based on the known lifecycles of other cynipid gall wasp species it is believed that this tiny wasp lays its eggs on the new growth early in the spring. As the larvae feed on the tissue, growth from the tree forms a woody chamber (gall) around them. When they are finished feeding they pupate into an adult wasp and chew their way out of the galls. The process of feeding and gall formation disrupts the vascular system of the branches and twigs, reducing the flow of water and nutrients. Damage is expressed as browning of foliage during the growing season, and dieback of twigs and branches that do not leaf out in the spring. Particularly heavy infestations may even result in the death of the entire tree.

While there was a similar outbreak in Long Island during the mid-1990’s there is still much to be learned about the treatment of these insects. Specific controls are being researched but it is believed that healthy, vigorous trees will remain more resistant to damage.

With this in mind, the first line of defense against this pest is to remove any other sources of stress to the trees. Proper irrigation during long dry spells, aggressive fertilization to deliver nutrients that aid in tree growth, the use of biostimulants such as ArborKelp^® and other soil amendments, and control of other insects and diseases will help to maintain vigor and reduce damage.

For trees that are particularly valuable, under stress, or that have been previously attacked, additional treatments may be needed in an attempt to control the insect directly.

Since this destructive insect is only susceptible to treatment early in the spring, SavATree recommends to clients that they talk to their arborist now to have their oaks inspected and a treatment plan developed that is tailored to their specific property.

To learn more about the cynipid gall wasp or discuss treatment options, contact your SavATree Cape Cod arborist.