Several borers will attack dogwood. Try to keep the trees healthy with regular fertilization. Indications of borer problems are holes in the trunk ,leaves smaller than normal, and dieback of the crown.
Dogwood club gall midge causes galls at the branch tips. The leaves on affected branch tips may be distorted and the branch may fail to form a flower bud. Prune out the galls as soon as they are seen. No chemical controls are listed for this insect.
Leaf miners cause brown blister-like mines on the undersides of leaves. The adult leaf miner skeletonizes the leaves.
Scales can build up to large numbers before being detected. Dormant oil will control overwintering stages. Active crawlers are controlled with Sevin or malathion. Identification of the specific scale will aid in timing crawler sprays.
Aphids may be controlled with sprays of malathion.