Dogwood trees are heavily used as ornamental plants and some species are commonly found as a native component of many woodlands. Dogwood trees are regularly attacked by borers, especially in ornamental landscapes. Examples of insect borers of dogwood trees include the dogwood borer, flatheaded appletree borer and the dogwood twig borer.
Borers typically lay eggs on a tree's bark. Soon the eggs hatch and the larvae chew into the tree. The borers feed on the tissue under the bark. The damaged tissue prevents water and nutrients from moving inside the tree, which can cause tree death or increase a dogwood's disease susceptibility. Additionally, some borer activity, such as from the flatheaded appletree borer, can reduce structural integrity and lead to main stem failure.
Several borer species attack dogwood trees. The clearwing moth Synanthedon scitula is the insect most commonly known as the dogwood borer. Other borers include the flatheaded appletree borer, Chrysobothris femorata; other flatheaded borers such as Chrysobothris azurea and Agrilus cephalicus; and the dogwood twig borer, Oberea tripunctata. Even though each of the aforementioned borers is a different species, they all cause the same type of damage.
Because the various borer species cause the same type of damage, signs and symptoms of infestation are generally the same. Symptoms of wood-boring insect activity include crown dieback and wilting shoots. Signs of borer activity include circular or oval exit holes, callus tissue, cracked bark, and sawdust-like material at the base of the tree or at bark cracks.
The most common control methods for dogwood boring insect are bark sprays and systemic insecticides. Pyrethroid sprays are the most commonly used treatments and must target egg hatching. Timing of spray application varies depending on species. Systemic, soil-applied insecticides such as imidacloprid can be used for some borers. Because borers often attack less healthy trees, maintain tree health with adequate watering, plant in an appropriate site, and prevent damage to the trunk.
Many insecticides are dangerous chemicals and all recommended safety precautions should be followed. Even though insecticides are developed for use against insects, severe toxicity can occur in humans and animals. Always follow label directions, and never use more than the recommended amount for the target insect listed. In many cases, using more of an insecticide than is recommended on the label does not provide better control.