Succulent oak galls are common in southern
Illinois on pin oak and shingle oak. These green,
marble-sized galls will shrivel and turn black in a few
weeks. No control is recommended.
Eriophyid mite galls are starting to appear on wild plum in
northern Illinois. They will develop into slender galls
about 1/8 inch long on the upper leaf surface. Control is
Cooley spruce gall eggs have been found on Douglas-fir in
northern Illinois. On Douglas-fir, this insect appears
throughout the summer as white, pinhead-sized, fluffy
aphidlike adelgids on the needles. This insect also attacks
spruce, causing galls to form on the ends of the branches.
Most contact insecticides will provide control.
Large numbers of eastern tent caterpillar have been found in
southern Illinois; smaller numbers have been seen in central
and northern Illinois. Control these insects by pruning or
pulling out the silk tents they spin in twig crotches. (Do
this during the night or on cloudy or rainy days when the
caterpillars are in the tents.) Control can also be achieved
with many insecticides, including Bacillus thuringiensis
kurstaki, sold as Dipel, Thuricide, and various other trade
(Other contributors to the article: staff at The Morton Arboretum)