The twigs and branches of hardwood trees are often attacked by various longhorned wood boring beetles and clearwing moths. Two common beetle species are the twig girdler, Oncideres cingulata, and the twig pruner, Elaphidionoides villosus (Figure 89 & 90). Both species attack oaks, hickories, pecan and many other species of hardwoods. Damage is often severe in pecan and other fruit tree orchards.
The twig girdler beetle chews around the outside of the twig until it is almost severed (Figure 89). Eventually these twigs will break and fall to the ground or may bend at the girdle and swing in the tree. The twig pruner’s girdle is made from within the branch or twig by the grub and there is no visible outside girdle (Figure 91). In both situations, however, the result is the same. Both twigs and branches are girdled.
The larvae of both species spend the winter in the girdled twig. A good method of control is to collect the twigs and branches that fall to the ground and burn them. Those hanging in the tree should be collected and burned as well. This should begin soon after the damage is noticed and continued through the winter months.
The dogwood twig borer, Oberea tripunctata, is a beetle that breeds in dogwood, sourwood, elm and various fruit trees. The adults appear in the spring and the females lay eggs in the smaller twigs of the tree. The larvae bore down the center of the twigs feeding towards the trunk (Figure 92). Infested twigs will often break. Local infestations can become severe on trees. Infested twigs should be pruned and destroyed.
The dogwood borer, Synanthedon scitula, is a clearwing moth that resembles a wasp (Figure 93). It is blue-black in color with two yellow abdominal bands. Adult emergence begins about the time dogwood flower petals fall and continues until September. Eggs are laid in damaged bark areas or in crotch areas of branches. Signs of borer infestation will be sloughing of bark, dieback and adventitious growth. Coarse brown frass is often pushed from the larval galleries and can be seen on the outside of the bark. The dogwood borer attacks numerous other hosts including pecan, oak, hickory, flowering cherry, willow, birch, and apple. Black knot fungus galls on Prunus spp. are also attacked. Populations of the dogwood borer can be monitored with pheromone traps.
The peachtree borer, Synanthedon exitiosa, is a clear winged moth that attacks several species of fruit and ornamental trees (Figure 94). The females lay eggs in bark crevices and scar tissue near the ground. The larvae upon hatching bore into the tree just above the ground line. Trees can be killed or severely weakened by the girdling action of the larvae. Trees skinned by lawn mowers or string trimmers are highly susceptible. Signs of attack are sap mixed with boring dust at the tree’s base.
The lesser peachtree borer, Synanthedon pictipes, is very similar in appearance to the peachtree borer, however, it attacks trees at many points along the trunk or larger branches. Therefore, any borer attacks occurring above the tree’s base will be that of the lesser peachtree borer.