Borers of Crab Apple Trees

Borer Types

• Crab apples are susceptible to infestation from the dogwood borer, the shothole borer, the roundheaded apple tree borer and the flatheaded apple tree borer. Borers are the larvae of moths and beetles that damage trees when they eat into the inner wood of twigs and trunks. The pests also infest and feed on roots.

Pest Description

• The dogwood borer moth is about 1/2 inch long with slightly longer white larvae with brown heads. The larvae create 3/4-inch-deep tunnels in the wood with their feeding. The shothole borer is a dark brown to black beetle with reddish brown legs. The white larvae with reddish-brown heads are legless with a body slightly enlarged right behind the head. The roundheaded apple tree borer is white and 1/2 to 1 inch long with equally long antennae. The larvae are 1 1/4 inch long, thin and cream colored with a brown head and a thickened area just behind the head. The flatheaded borer adult is a greenish-copper colored, oval, 1/2-inch-long beetle with a blunt head and a tapered end. The white larvae are about an inch long with a distinctly flat segment behind the head.

Damage

• The larvae of the dogwood borer create 3/4-inch-deep tunnels in the wood with their feeding. The larvae start to eat into the wood and aerial roots of the tree right after hatching. Shothole borers feed into sapwood and create round holes into the bark as they emerge at maturity. Shothole borer beetles are able to fly long distances. Roundheaded borers are likely to infest both unhealthy and healthy trees and infest the areas between the bark and sapwood, creating 3- to 4-inch-long tunnels as they feed. Flatheaded borer larvae also create 3-inch-long tunnels in the outer sapwood as they feed.

Control

• Keep trees in good health and avoid unnecessary damage to the trunk and roots. Plant tree varieties adapted to your area. Monitor trees regularly to start remedial strategies before the infestation gets worse. Do not prune trees between late winter and late summer as this is the time when adult borers are most active. For insecticides to be effective, you have to apply them at the time when the adults are laying their eggs. No insecticide will affect the borers once they are inside the tree. Recommended insecticides include carbaryl and pyrethroids.