Why Are the Tips Falling Off of My Tree Branches?

Every fall, Extension offices around the state receive calls from homeowners concerned about branch tips on oaks, hickories, persimmons and various other tree species falling to the ground. While there are several possible causes for this annoying phenomenon, the most common are two "long horned" beetles commonly called the twig girdler or twig pruner. The name "long horned" refers to the long antennae of these insects, which are as long as the body. The terms "girdler" and "pruner" refer to the damage done by the insects leading to breakage and falling of branch tips. For both insects, the end result of their activities is the creation of dying branch tips suitable for overwintering of larvae within.

Twig girdler differs from twig pruner in that the girdling is performed by the adult female beetle as she prepares the branch tip for egg laying. During this process, the twig girdler chews a V- shaped groove encircling the branch tip, thus weakening the tip and making it susceptible to breakage by wind. However, before the tip falls, the female deposits an egg under the bark of the soon-to-fall branch tip. The eggs hatch, burrow into the fallen twigs and overwinter as small larvae. The larvae feed during spring and summer of the following season, pupate and then emerge in late summer as adults to start the cycle again.

While the twig pruner also causes branch tips to fall, it does so in a different way. Rather than cutting grooves to lay eggs, the female twig pruner chews holes near the branch tips in spring to deposit eggs. When an egg hatches, the larva bores toward the center of the twig. When mature, in late summer, the larva chews outward from the center of the branch, stopping at the outer bark. As with the twig girdler, branch tips weakened by twig pruner damage often snap off, either falling to the ground or hanging down by attached pieces of bark.

For both of these insects, diagnosis is reasonably straight forward. It should be possible to find a larva in each fallen branch. In the case of twig girdler, the broken twig will have a smooth outer edge with the center of the break being ragged. In the case of twig pruner, the break on the branch tip will have a smooth center and a ragged outer edge. Fallen branch tips created by twig pruner damage may be up to 2 inches in diameter. In either case, the most effective control is to destroy all fallen branches to break the life cycle of the insect. It is generally not practical to use chemical controls.

For more information on twig girdler and twig pruner, see the following web page: http://muextension.missouri.edu/xplor/agguides/pests/g07276.htm.

Chris Starbuck, Woody Ornamental Horticulture, UMC (573) 882-9630 Center, (573) 443-4893