Aphids of various types feed on hickory causing distorted and stunted growth. The hickory leaf stem gall aphid causes the formation of hollow green galls on leaves, stems, and twigs. The galls form in June and turn black in July. The galls are up to a half inch in diameter. Aphids are controlled with a dormant oil spray applied in early spring. At other times use malathion.
Hickory bark beetles mine the bark and sapwood. The boring cause wilting of young twigs or trunks may be girdled and trees killed. Keep trees healthy by fertilizing regularly and by watering during dry weather. No chemical control is registered for this pest.
The twig girdler larva girdles twigs causing weakened twigs to break off and drop. The larva is about a half inch long and rides the branch to the ground where it overwinters. Gather the fallen twigs and destroy them. No chemical control is registered for this insect.
June beetles eat the leaves of hickory at night. The injury is usually not severe but can be mysterious since no insects are seen during the day. No chemical controls are listed.
Caterpillars of various types feed on hickory. Some caterpillars can be controlled with sprays of Bacillus thuringiensis, a bacterial disease affecting some types of caterpillars.
Scales of various types attack hickory but can be controlled with sprays of dormant oil. Crawlers can be controlled with sprays of Sevin.