made of plant tissue. They are
produced in response to attacks by a gall making insect.
|In the war
between insects and plants, gall making represents a truce. Most gall makers do not harm plant health.
oak gall (pictured) is an exception.
GALLS Callirhytis cornigera (Osten Sacken). This tiny wasp gall
maker causes trees to produce large numbers of woody galls up to 2 inches in
diameter around the stems of pin and willow oak trees. These galls will
girdle and cause significant branch dieback. Female wasps emerge from woody
galls in early spring (April) and lay eggs into the
swelling leaf buds. Eggs hatch
into larvae that cause a blister like gall along the veins
superficially resembling the vein pocket gall of pin oak. In summer
(June) adults fly from leaf galls and lay eggs into twigs. The
resulting galls become visible the
following spring and finish development in about 3 years. Dogwood
borers may also feed in young woody galls. Control.
Remove young expanding twig galls as soon
as they are visible in the spring. Cutting off old dried galls is not
necessary. Applications of insecticides can kill leaf galls, but do not
reduce the number of new stem galls produced.