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Scouting Report 5/6/98

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 not recommended.

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 names.

(Other contributors to the article: staff at The Morton Arboretum)

Author: Phil Nixon Fredric Miller


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