Gypsy moth is becoming more numerous in northeastern Illinois. Infestations have risen high enough in Lake County, the most northeastern Illinois county, that it is in the process of being quarantined. The quarantine will restrict the movement out of the county of nursery stock, firewood, household belongings, and other materials.

Lake, Cook, and DuPage counties, including Chicago, and many suburban areas may contain too many gypsy moths for meaningful eradication efforts. The southwestern portion of DuPage County, including Naperville and some nearby townships, has low enough numbers for trapping and eradication efforts to continue.

The Illinois Department of Agriculture (IDA), in cooperation with the USDA Animal and Plant Health Inspection Service, USDA Forest Service, and local groups, has operated an eradication program in Illinois since the 1970s. The program has reduced tremendously the amount of tree injury that would have occurred due to gypsy moth and the amount of insecticide that would have been used to control the insect in Illinois during that time. Their aggressive program in detecting, delineating, and eradicating small, pioneer populations of gypsy moths has been copied by many other states, and Illinois residents should be very proud and appreciative of its activities.

However, over the last decade, a long-standing infestation in central Michigan has spread to include much of southwestern Michigan with relatively high numbers of gypsy moth. Strong evidence exists to suggest that caterpillars have blown across Lake Michigan into Illinois and Wisconsin, particularly in Door County, Wisconsin. Increased appearance of gypsy moths in northeastern Illinois, due to influx of gypsy moth from Michigan, Wisconsin, and other areas by natural and incidental human activities, has resulted in the establishment of this insect in parts of Illinois.

In response, IDA has had to change its approach to a program called “Slow the Spread.” This involves the reduction of pheromone trapping and eradication activities in areas such as Lake, Cook, and most of DuPage counties, where gypsy moth numbers are too high for eradication to be practical. It allows the concentration of financial resources and personnel efforts on detection and eradication of gypsy moth in Illinois outside of that area. IDA remains committed to assisting local residents, governmental units, and community groups in suppressing and locally eliminating gypsy moth infestations in Lake, Cook, and DuPage counties but is unable to totally fund and execute these programs.

Residents, landscapers, governmental units, and others who wish to provide their own control efforts directed at gypsy moth are free to do so in Lake, Cook, and most of DuPage counties. IDA is very interested in finding out where these activities occur and where infestations of gypsy moth are located in these counties and anywhere else in Illinois. Contact the IDA office in Des Plaines at (847)294-4343, or contact your local University of Illinois Extension office and they will contact IDA. Again, IDA is willing to assist in control efforts in these three counties but recognizes that others are able to respond quickly to infestations and provide quality control as well.

At this point, gypsy moths have laid their egg masses, and most of the adult moths have died. The egg masses are about 1 inch long by 1/2 inch wide and look like buff to tan felt patches. Females lay egg masses on tree bark and other exposed surfaces but also commonly underneath loose bark, beneath house siding, within hollow areas of swing sets, in car wheel wells, and in other hidden locations. Egg masses should be scraped off and dropped into rubbing alcohol or soapy water. Dispose of them in the trash.

Next spring, the eggs hatch, with spray applications most effective when the oak leaves are expanded about halfway. In northeastern Illinois, this is usually in mid-May. Effective insecticides against the larvae include Bacillus thuringiensis kurstaki (Dipel, Thuricide), cyfluthrin (Tempo), diflubenzuron (Dimilin), tebufenozide (Mimic), and many others.