Honeylocust plant bug is being reported in large numbers in DuPage County in northeastern Illinois. I appreciate the calls from several professional horticulturists to correct my earlier statement that these plant bugs seemed to be low in number. Treatment at this late date, when the insects are in the adult stage, may not be very profitable; however, treatment should keep the damage from getting worse. The adults will fly away when spray is applied but will return to be killed by the active residue. Therefore, synthetic pyrethroids should be effective, but insecticidal soap and summer spray oil are less effective because they must come into contact with the bug to achieve control.
Masses of webbing two to three inches across filled with frass (insect feces) are numerous in some areas of northeastern Illinois. It appears that this is caused by the pine false webworm (a sawfly). This caterpillar-like larva is light in color with three pairs of true legs but no prolegs. Pine webworm causes similar damage but is brownish with five pairs of prolegs, as well as three pairs of true legs. The important thing to remember is that sawflies are not controlled with Bacillus thuringiensis kurstaki (Dipel, Thuricide) but are controlled with various chemical insecticides. Use high pressure to penetrate the webbing.