Issue 8, June 11, 2010

Scouting Watch

Bagworms have hatched throughout Illinois. Look for bagworms one-eighth to one-quarter inch long feeding on the foliage before treating. Also look at the top of the tree for evidence of silk strands about three feet long. When bagworms hatch, they climb to the top of the tree, spin out long silk strands, and ride it to new hosts. They typically do this for about two weeks and then start to feed. In southern Illinois, usually ballooning stops and feeding starts around the middle of June, occurring in early July in central and northern Illinois. This year, with our accelerated spring, the bagworms appear to have stopped ballooning and started feeding heavily already in southern and central Illinois. Scout for this in northern Illinois. Once ballooning stops and feeding starts, spray with Bacillus thuringiensis 'Kurstaki' (Dipel, Thuricide, others) or other labeled insecticide to provide season-long control with one application. Spraying too early usually requires more than one application.

Earwigs are already numerous throughout Illinois, a couple of weeks earlier than usual. Earwigs feed primarily on dead organic matter, but are also predators and plant feeders. Severe leaf and petal feeding can occur on roses and many thin-leaved herbaceous flowers such as daylilies, impatiens, hosta, violets, petunias, salvia, and pansies. Carbaryl (Sevin) or labeled pyrethroids are effective on the foliage for control. Do not treat the blossoms, even if the earwigs are eating them, to avoid killing bees and other pollinators.

Grass sawfly larvae are feeding on various species of Lysimachia, sometimes called loosestrife or creeping jenny in northern and central Illinois. These plants should not be confused with purple loosestrife, which is in a different genus. The sawfly larvae are whitish to pale green with light tan heads and obvious black eyes. Fully grown larvae are a little over one inch long. Although sawfly larvae look similar to caterpillars, they have more than five pairs of prolegs. Not being true caterpillars, they are not controlled with Btk. Spraying the foliage with carbaryl, Sevin, or a labeled pyrethroid will provide control. Do not spray the blossoms to avoid killing bees and other pollinators.

--Phil Nixon, Greg Stack, Mike Greifenkamp

Phil Nixon

Return to table of contents