Hickory Leaf Stem Gall Aphid
Contact: Eric Day, Manager, Insect Identification Laboratory
Publication 444-248, August 1996
Hickory Leaf Stem Gall Aphid
Plants Attacked
Hickory
Description of Damage
The Hickory Leaf Stem Gall Aphid (HLSG) damages trees by causing
the development of galls, or swellings, on petioles and
occasionally new shoots of hickory. In spring and early summer
the galls are green, leathery, and bullet shaped, varying in size
from a pea to 1/2 inch or more in diameter. The galls may be
round or irregular in shape. The tree owner becomes concerned
when in mid to late summer, the leaves fall prematurely.
Identification
The best way to identify the HLSG is by the gall or damage that
it makes. The actual aphid is very small and whitish to greenish
in color. The aphid produces considerable waxy secretions inside
the gall. The Hickory Leaf Stem Gall Aphid, Phylloxera
caryaecaulis, is in the order Homoptera, family Phylloxeridae.
Life History
Eggs hatch as new buds open and grow in the early spring. Young
aphids crawl to newly expanding foliage where they feed on the
new growth by piercing the epidermis and sucking cell sap. The
feeding causes the tissue to grow galls which enclose the aphids.
Several generations of aphids develop within the galls during
May, June, and into July. In late July, the galls split open,
turn black and jagged in appearance, and the aphids emerge. At
this time most of the affected leaves fall prematurely. There
are several generations of aphids per year. Eggs are laid in
late summer or fall in cracks and crevices of the bark and in old
stem galls. Aphids overwinter as eggs in the gall and bark
crevices.
Control
Malathion sprays have been suggested when the buds have expanded
to about 1/2 inch and are beginning to show green. However,
reports indicate this treatment may not be very effective.
Determining the exact timing is difficult and it is unlikely all
aphids will be hit with insecticides. No other control measure
have been developed. Late in the summer when leaf drop is
noticed, it is much too late to take action.
Remarks
This pest is not likely to cause serious damage to mature trees.
Premature leaf drop alarms tree owners, resulting in calls and
questions, but rarely is control needed on these large trees.
However, the HLSG can cause major damage to small, newly
established trees and trees in nurseries. Control should be
considered if the tree is not big enough to withstand attack.