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Scouting Watch

June 9, 2004

Gypsy moth larvae are getting large enough in northeastern Illinois to cause noticeable feeding injury. Look for branches at the tops of oaks and other trees being stripped of foliage. Bacillus thuringiensis kurstaki (Dipel, Thuricide) should still be effective on smaller caterpillars, but spinosad (Conserve) or a pyrethroid may be needed to control larger larvae.

Mimosa webworm first generation should be noticeable in the southern half of Illinois and along the Lake Michigan shore. Other areas in northern Illinois where there has been previous damage should also be checked. Honey locust is attacked throughout the state, as well as mimosa in southern Illinois. Damage of this first generation appears as a few leaflets webbed together, with window-feeding damage on the leaflets. Separating these webbed leaflets reveals green to gray caterpillars up to one inch long. From a distance, damaged trees appear to have light or reflective spots in the foliage where feeding damage is occurring. Insecticides suggested for gypsy moth are effective, but coverage must be thorough to get the insecticides to the larvae. Treating now reduces the more damaging second generation in July.

Flea beetles continue to be reported damaging rose, evening primrose, hosta, and other flowers throughout Illinois. Tiny holes rapidly expand to large brownish areas. Carbaryl (Sevin) and labeled pyrethroids are effective against these insects. Be sure to avoid spraying blooms to avoid killing beneficial nectar and pollen-feeding insects.

Ash flower gall is being sent in to the Plant Clinic from several areas of the state. Eriophyid mites attack the male flower on ash, causing clusters of prickly, roundish, green galls up to 1/2 inch across, which appear somewhat like miniature sweet gum balls. These galls soon shrink and turn brown, with no harm to the tree; treatment is typically not warranted.

Author: Phil Nixon


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