Spread of the gypsy moth continues across state

By 2018 the slow spread of the gypsy moth covered the eastern three-quarters of Wisconsin. The bug is continuing its slow flight of almost 160 years west from Boston, where it arrived in the U.S. in 1869.

But the Wisconsin Natural Resources Board deactivated an aerial spraying program to ward off the infestation in action taken August 8. This was after the DNR program had sprayed in 16 Wisconsin counties to forestall further westward flow of the infestation.

The program was deactivated because of low demand, and the availability of private sector alternatives to the program, according to Bill McNee, a plant pest and disease specialist with the DNR. Aerial crop sprayers who can undertake the process on forest land are licensed by the Wisconsin Department of Agriculture, which has information on licensed sprayers.

Most gypsy moth infestations don’t warrant the expense of spraying because the mortality rate among trees is likely to be quite low, McNee said, and mainly trees with other health issues don’t survive. Mixed species forests in which good forestry practices have been employed are unlikely to be affected. However, a more likely candidate for spraying is a hardwood forest with a good percentage of likely veneer trees.

The insecticide used in the suppression program is a formulation of the bacterial insecticide

Bacillus thuringiensis kurstaki (Btk). “Btk is a naturally occurring bacteria found in soil that is harmless to people, animals, and even other insects” according to the DNR.

The Natural Resources Board cited a DNR recommendation in suspending spraying operations due to “private sector alternatives”, per the DNR.

A gypsy moth infestation can lead to defoliation of some or all of the affected trees. The insects prefer to feed on alder, aspen, birch, oak, basswood and tamarack. However, their feeding habits can be broader including some conifer species, according to the DNR. Tamarack are particularly susceptible, according to McNee.

The gypsy moth egg masses are quite visible as furry looking white ovals of an inch to an inch and a half.

Late autumn or winter is the right time to predict whether a forest owner will have a gypsy moth event, according to the DNR. Here’s their recommended process:

“When leaves have fallen, enter areas of concern in your woods with a stake with an 18’ ½” string attached. You can use the string to mark off a survey area of approximately 1/40th of an acre. Also bring binoculars, a notebook and pencil.

Examine the trees within the circle looking for and counting gypsy moth egg masses. Don’t forget to examine the higher portions of trees with the binoculars. If you count more than 25 egg masses within your circular survey area, the area is likely to experience a defoliation event next summer.”

Gypsy moth events are likely to occur during May, June and early July. Trees that are more than two-thirds defoliated are likely to grow new leaves during the summer. Infestations weaken trees but are generally not fatal.

For more information or to report a Wisconsin infestation in 2019, you can call 1-800-642-moth or check for information at gypsymoth.wi.gov