Bagworms can still be treated. If the bags are 1 inch long or less, Bacillus thuringiensis kurstaki (Dipel, Thuricide) should still be effective. Cyfluthrin (Tempo) is more effective on larger bagworms, as well as being effective against smaller larvae.
Twospotted spidermites and related spidermites are likely to become prevalent with the recurring hot, dry weather. Cotoneaster, honey locust, oak, and maple are likely to show damage first, so keep your eye on them. Older foliage will appear somewhat grayish from a distance. Closer inspection will reveal whitish to brown stippling on the upper leaf surface, and the lower leaf surface will appear dirty. Using a hand lens will verify that the “dirt” on the underside consists of spidermites, their cast skins, and fecal matter. Abamectin (Avid), acequinocyl (Shuttle), befenthrin (Onyx, Talstar), etoxazole (TetraSan), hexythiazox (Hexygon), insecticidal soap, spiromesifen (Forbid), and summer oil are effective. Insecticidal soap and summer oil require through coverage and two weekly sprays.
Mimosa webworm is an annual problem in southern Illinois and sporadic in central and northern Illinois. Check honey locust for leaflets or leaves that are webbed together and are brownish from feeding damage. In southern Illinois, also check silk tree or mimosa. If infestations are numerous, apply acephate (Orthene), Bacillus thuringiensis kurstaki (Dipel, Thuricide), carbaryl (Sevin), or spinosad (Conserve). Spray thoroughly to get the spray inside the webbed leaflets and leaves. Small infestations create large damaged areas later in the summer.