Falling Limbs Caused by an Insect

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Have you ever found a nearly perfectly cut tree branch, about the size of your little finger, falling out of trees and on the ground?

Each fall I’ll get more than a few calls about such an event. Many times, the caller is just a little hesitant or maybe reluctant to say to say that something peculiar has been trimming their trees.

Even without seeing the offending insect, this can easily be identified as a twig girdler, Oncideres cingulate.

Twig girdlers are a pest of pecan and hickory, and to a lesser extent several other hardwood trees. The adult beetles girdle twigs and small branches causing the injured portions to break away or hang loosely on the tree. It is not uncommon to see the ground under infested trees almost covered with twigs that have been cut off.

Girdling affects the beauty and aesthetic quality of ornamental plantings. With pecans, the fruiting twigs of heavily infested trees are often reduced, resulting in lower nut yields the following year or years.

During late summer and fall, the presence of severed twigs on the ground or hanging loosely attached or lodged in the canopy is good evidence of twig girdler activity. Most girdled twigs are from 1/4 to 1/2 inch (occasionally up to 3/4 inch) in diameter, and 10 to 30 inches long.

The nature of the girdle itself distinguishes the twig girdler from other branch pruners. The cut by the twig girdler is the only one made from the outside by a beetle and is seldom complete, leaving a small central cylinder (this leaves a central jagged area when the twig breaks).

The girdling extends through the bark and well into the wood in a complete circle around the stem and leaves only a thin column of the center wood attached. Since the twigs are girdled while the leaves are present, the severed twigs retain the brown leaves for some time. Severed twigs lodged in the tree canopy or on the ground and often retain leaves even after the tree sheds its leaves in the autumn.

Close inspection of the severed twigs will reveal tiny egg niches and many mandible marks or grooves made in the bark by the female beetles. Large trees usually sustain the most girdling, but young trees are sometimes heavily damaged.

The adults emerge from late August to early October. They feed on the tender bark near branch ends and mate before ovipositing and girdling the twigs. The branches are apparently girdled by the female so that proper conditions will be provided for the development of the larvae.

Eggs are laid during or after the cutting process, but never before the beetle makes part of the cut. They are inserted singly beneath the bark or slightly into the wood, usually near a bud scar or adjacent to a side shoot. The number of eggs per twig varies from 3 to 8 but may range up to 40.

Adult twig girdlers live 6 to 10 weeks. Females deposit 50 to 200 eggs each, which hatch in about 3 weeks. After overwintering, the larvae grow rapidly in the spring and tunnel toward the severed end of the twig by feeding only on the woody portion and leaving the bark intact.

Your best method of control is picking up the severed twigs on the ground as well as those lodged in the trees. Gather them and burn them or simply throw them away. If possible, be sure to do the same in nearby wood lots containing oak and hickory when nearby plantings have a history of serious damage from this insect pest.

Insecticide is rarely justified or practical. Insecticides may be necessary to prevent damage from heavy infestations in some hardwood tree nurseries. These may be applied once or twice in September and again in October as a protectant to reduce the majority of the twig girdlers.

Picking up the affected twigs can greatly reduce the interesting pest in one or two seasons.

Author

Cary Sims
Cary Sims

Cary Sims is the County Extension Agent for agriculture and natural resources for Angelina County. His email address is cw-sims@tamu.edu

Educational programs of the Texas AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin.

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