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Scouting Watch

June 5, 2002

The warmer weather of last week is speeding up the insects, so be on the lookout for not only new insects but also some that came out a couple of weeks ago.

Periodical cicada remains active in southern areas of the state where this brood has emerged. Numbers are high in southwestern Illinois in Randolph, Madison, and St. Clair counties. We have reports from Crawford and Lawrence counties in the southeast. Typically, males sing and mate with females for about 2 weeks, males die (causing the singing to stop), and then females lay eggs. As the singing abates, it is time to protect young trees with trunks less than 2 inches in diameter. Wrap the trunks with tree wrap or mesh. If using mesh, let it stand off the trunk an inch or two to avoid the cicadas' laying eggs through the mesh. Fe-males lay eggs for 2 to 3 weeks, so keep protection on at least that long. In heavily infested areas, the ground becomes littered with dead cicadas. Remember, insec-ticide use may look impressive, but cicadas flying in later are still likely to cause serious trunk injury.

May beetle adults are feeding at night on the leaves of crabapple, oak, ash, and other trees. If you are see-ing the edges of leaves eaten away, sometimes to the midvein, with no insect in sight, look at the tree after dark. You may see hundreds of beetles feeding; during the day, they burrow into the soil. The most common species of adult May beetles, or true white grubs, is about 1 inch long, heavy bodied, and reddish brown to dark brown. One species is tan and 1/2 inch long--looking like the adult masked chafers or annual white grubs. We had a likely report of this insect in northeastern Illinois; they occur throughout the state, particularly in southern Illinois. Carbaryl (Sevin), as well as several other labeled insecticides, is effective against this feeding.

Bronze birch borer is still treatable with dimethoate (Cygon), imidacloprid (Merit), and permethrin (Astro, Ambush, Pounce). Birch leafminer is active; treatment may be needed in far northern Illinois, where damage can be severe. Cygon is effective, and Merit should also provide good control. Hawthorn and alder leafminers are also active, but populations are typically too low to merit treatment. Woolly alder aphids and larch adelgids are active in northeastern Illinois.

Author: Phil Nixon Jim Fizzell Morton Arboretum


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