For information regarding identification and control of Japanese beetles, we recommend the article Japanese Beetle Management in Minnesota by UMN Horticulture Extension
We recommend 12-month Tree & Shrub Insect Control by Bayer for year-long insect control. This systemic pesticide is taken up by the roots and needs only to be applied once per year. It can take up to three months for large trees to be protected. Therefore, it is best to apply well before any infestation occurs, such as in early fall.
Homeowner's Guide to Managing the Japanese Beetle by the USDA (PDF)
Japanese Beetles have been a major garden pest in recent years. As their name suggests, these beetles are not a part of the native Wisconsin environment. Japanese beetle grubs will feed below ground on turfgrass roots, while adults will defoliate over 300 species of trees, flowers, fruits on vegetables.
Image courtesy of David Cappaert, Michigan State University, Bugwood.org