GYPSY MOTH ACTION ALERT

Gypsy moth caterpillars – which emerge from egg masses by the hundreds in the spring of the year – can feed on nearly 500 different kinds of trees, preferring oak, poplar, and birch. Approximately every 10 years or so, their populations explode and the damaging effects of their feeding is most evident. During these outbreaks, the caterpillars can strip entire trees bare in a matter of days, ravaging neighborhoods or even entire forests by late June. While most healthy trees can survive a single defoliation, trees that are already stressed by drought or other factors that same summer may die. At this level, the caterpillars themselves can be quite a nuisance for some people as the tiny hairs on the caterpillar can cause some people to suffer allergic reactions. These outbreaks may last as long as three years. And while it remains unclear what causes populations to explode, they always eventually collapse as a result of natural causes.

During these outbreaks or the period in between, homeowners and landowners alike can take steps to help reduce the damage that these insects cause. The time of year will dictate which strategy to employ as the different life stages of the gypsy moth require unique methods.

In the fall of the year, after leaves are off the trees, search out and destroy egg masses. Gypsy moth egg masses are teardrop-shaped and buff tan in color. They are covered with tiny hairs from the adult female moth’s abdomen. They are usually found in protected areas like the cracks and crevices of rough bark, but can be found on just about anything – including cars, picnic tables, grills and playground equipment – in your backyard or property. Use a knife to scrape them into a jar and cover them with an equal mixture of vegetable oil and water. Discard the contents of the jar into your trash after a few days. For egg masses that you can’t reach, spray them with a horticultural oil. This will coat and suffocate the eggs.

In the spring, prior to the middle of May, a "sticky band" around suspect trees can help stop caterpillars in their tracks when they try to crawl up the tree after falling out of it. Caterpillars frequently fall out of trees during dispersal or in reaction to disturbance or a threat. Wrap duct tape around the tree at chest height and several inches wide. Be sure to push it into the contours of the bark. Spread a band of a horticultural-grade sticky barrier material (like Tanglefoot®) or petroleum jelly on the tape. Be sure to check every few days to make sure that the band is not covered with dead caterpillars or debris which would allow caterpillars to safely cross over it. If that occurs, scrape off the debris and replace with fresh, sticky material. Never use automotive grease with your band; it can kill trees.

In June, when caterpillars are larger, a burlap collection band can replace the sticky barrier band. Wrap a piece of burlap, about two feet wide, around the tree and tie a piece of rope or twine around the middle to keep it in place. Let the material above the rope drape over the bottom part, making a shelter for caterpillars to hide during the day. Check under the burlap daily from mid-afternoon to early evening and collect all the caterpillars that you find. Place them in a jar of soapy water and discard after a few days. Or you can cut the caterpillars in half. Be sure not to handle the caterpillars with bare hands as their hair can trigger an allergic reaction in some people. Take the bands down in late July or August when gypsy moth caterpillars have pupated.

For a complete discussion of these methods and other control options, please visit the Wisconsin Cooperative Gypsy Moth Internet site at www.gypsymoth.wi.gov. You will find there a wealth of information regarding the management and control of gypsy moth, images to aid in identification, a list of contacts for assistance, and links to a variety of publications and resources from local, state, and federal agencies. Another resource is the statewide toll-free gypsy moth information line. The number is 1-800-642-MOTH (6684). Calls to this line are returned by a program staff person from the Wisconsin DNR or the Wisconsin Department of Agriculture, Trade and Consumer Protection.

The gypsy moth is firmly established in the eastern half of Wisconsin, and outbreaks are possible in this area (as of 2005). There are considerable efforts underway in the western half of the state to slow the spread of this invasive species across the state.

The DNR and DATCP both coordinate aerial spraying programs to combat the spread or defoliating effects of gypsy moth. The DNR works to suppress outbreaks and limit defoliation in the eastern half of the state, while the Department of Agriculture manages a federal program called Slow the Spread in the western half of the state. For additional information on these programs, contact the appropriate state agency at either the Web site or the telephone number listed above.

Composed by Michael Swarok, WI-DNR, (608) 266-2172.
May 2005