Lawn Tips & Tricks

The Gall

We recently received a phone call from a customer on Cape Cod looking for information and spraying for Winter Moth caterpillars on her Oak Trees. The call was unusual because it was late summer- Winter Moth Caterpillar are a spring pest. The woman  had only recently noticed  the leaves on the ends of the limbs were sparse along with  clusters of leaves and broken twigs strewn around her property.  She, as many local residents were not pleased to hear there is a new pest in town that is doing  a tremendous amount of damage to oak trees. The culprit was not a caterpillar but a far less conspicuous predator, the 1/16 of an inch Bassettia ceropteroides or more commonly known, the Crypt Gall Wasp. Females lay eggs into the vascular system of tree branches, where larva develop. Encased in the branch, they are protected from predators and are fed by the tree. The wasp secretes saliva which sends a genetic message to the tree to produce woody material instead of producing leaves. This is what forms the tell tale gall that appear to be just swollen twigs on the tree. The twig gall prevents nutrients and water from getting to the leaves and branches of the trees. It also prevents the exchange of sugars vital for the life of a tree and is the perfect hiding place for these tiny parasitic insects. While insecticide treatments are still being investigated, there are cultural practices that can increase the vitality of your trees.  First, keep your trees well watered.  Remember, roots reach out to the drip line of trees so a good soaking is important.  Second, fertilize.  Extra nutrients will help the trees to recover from a pest like this.  Finally, treat for pests and diseases that can be controlled.  Often times it is secondary pests like the Gall Wasp that will give the final death blow to a tree that has been suffering from defoliation, drought stress or disease that has gone untreated.

Swollen twigs also known as galls protect the invasive Crypt Gall Wasp.

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