Landscape - Borers that Attack Trees and Shrubs

There are a number of borers that attack trees and shrubs in Delaware. The following is an article on the subject.

Most borers only attack stressed, injured, or diseased trees and the drought we experienced last year stressed trees for this season's emerging borers.

CLEARWING BORERS: Adult clearwing borers are day-flying moths often looking like bees or wasps. The larvae are usually cream colored with five pairs of prolegs on the abdomen and are found in either trunks or stems. Peachtree borer (adults: 340-2757 GDD), lilac/ash borer (adults: 159-4642 GDD), dogwood, and rhododendron borer (adult: 509- 3040 GDD) are all examples of clearwing borers. Old pupal skins may be found sticking out from the trunk or branch and emergence holes are round.

FLATHEADED BORERS: Metallic wood borers are elongate somewhat flattened beetles with a metallic sheen. The first thoracic segment is enlarged and legs are greatly reduced. Larvae feed just under the bark and often have zigzag tunnels filled with tightly packed sawdust-like frass. Bronze birch borer (adult: 513-2276 GDD) and two-lined chestnut borer (early June August) are examples. Emergence holes are often D-shaped.

ROUNDHEADED BORERS: These beetles are generally large and have long antennae, sometimes longer than the body of the insect. Adult color varies between species, dull brown or gray to bright coloration. Larvae have greatly reduced legs, are cream to light yellow colored, and relatively uniformly cylindrical. This group tunnels into the heartwood of the tree and the galleries are oval-shaped in cross section. The roundheaded apple tree borer (June July), locust borer (adult: 2597 3070 GDD), and redheaded ash borer (June) are examples. Emergence holes are oval-shaped to round.

CONTROL: Control is difficult especially once insects are inside the tree. Natural enemies include birds and a couple of parasitoids. Bark/trunk sprays of binfenthrin (Onyx) and permethrin (Astro) are often used. Imidacloprid as a soil drench has been efficacious against the flatheaded borers when applied shortly after egg hatch. Tree injections may also be used to control borers.

Information from Brian Kunkel, Ornamental IPM Specialist, UD