A.: I have exactly the same problem, and for years I have blamed it on the squirrels. I have lots of them. After all, they do dig holes in my yard, dig up my pots, eat the plastic parts of my grill, eat holes in my cushions and pull the stuffing out, and even gnaw on my deck and porch railings. Imagine my chagrin when I recently found out that they are not responsible for chewing off the ends of my tree limbs!
The culprit is a twig girdler (Oncideres cingulata). The twig girdler is a ½-5/8-inch-long horned beetle whose antennae are longer than his body. Its cylindrical body is grayish-brown with a broad ash-gray band across the middle of the wing covers. It primarily infests pecan and hickory trees, but will also attack persimmons and hackberries, as well as other hardwoods.
The pattern of the girdle where the twig girdler cuts it from the branch is made from the outside of the branch inward, resembling mini beaver damage. It is the only branch pruning insect that has this pattern and is distinctive from squirrel damage. It girdles the branch tips while the leaves are still present and they remain on the severed section for a prolonged period of time.
It is most common in the southern states, but exists northward to New England and westward to Arizona. The adult chews the ends of the branches, causing them to fall off or hang loosely on the tree. The damage is not usually a big problem for the tree. It affects the appearance of ornamentals and reduces the fruiting of nut-bearing trees the following year. Their repeated girdling causes the limbs to develop excess branching and forking, resulting in deformities in young orchards.
The main symptom of infestation you will see is severed twigs hanging from tree limbs or laying on the ground under the tree in late summer or fall. The female lays her eggs in the tips of the branch and then chews around the branch leaving a small area attached, which breaks off in the wind. Most of the girdled twigs will be from ¼ to ½ inch in diameter and 10 to 30 inches long. The twig is seldom cut completely, but retains a small jagged center where the limb breaks. Close inspection of the twigs reveals tiny egg niches often near a bud scar or side shoot and bite marks or groves in the bark made by the female beetles. Large trees usually have the most girdling, but young trees may sustain more actual damage.
Twig girdlers produce only one generation per year. The adults emerge between late August and early October and feed on the tender bark near the ends of the branches. Then they mate, lay their eggs and girdle the twigs. They lay between three and 40 eggs per branch. The adults live six to 10 weeks with the females laying between 50 and 200 eggs each. The eggs take about three weeks to hatch. In the spring, the rapidly growing larvae tunnel toward the severed end the limb, eating only the woody portion and leaving the bark intact. They then pupate in August and September and begin the cycle again.
The best control is to pick up any twigs under the trees and discard or destroy them before the eggs hatch or the grubs emerge in the spring. This practice will greatly reduce the population in a season or two. It is rarely justified or practical to apply an insecticide.
For more information on twig girdlers, contact the Carroll County Office of the University of Georgia Extension Service 770-836-8546. Maybe they can help with the squirrels, too!