Japanese Beetles

From:  Kevin Schoessow, UW Extension Area Agriculture Development Educator, Spooner Agricultural Research Station

​Japanese beetle a voracious defoliator of many landscape and garden plants has been confirmed in many locations in NW Wisconsin in recent weeks.  While very common in other parts of the state, this pest has not been known to be in our region until recently.  Adults beetle feed on over 300 species of plants.  Roses, birch, lindens, grapes, raspberries, Norway maples, beans, apples, plums, crabapples, elms, beech, asparagus, and rhubarb are some of its favorite species.  Adult beetles emerge in early to mid-July and feed for about six to eight weeks.  This feeding is quite noticeable and concerning especially on prized perennials and on fruits and vegetables.  Japanese beetle are tough to control, especially when bees and other beneficial insects are active during the same time.  Gardeners need to be cautious in their management decisions and be aware of unintended consequences of treatment options.
 
To help gardeners and homeowners make informed decisions about management options for Japanese beetles the following resources should be very helpful.
 
The first is a wonderfully insightful webinar presentation by PJ Liesch, Entomologist and Director of the UW-Madison Insect Diagnostic Lab.  The recorded presentation can be found on the Wisconsin Horticulture Division of Extension website https://hort.extension.wisc.edu/videos/  or directly through youtube at https://www.youtube.com/watch?v=TFFZs2gLAfs
 
The other is an article title Japanese Beetle
 
https://hort.extension.wisc.edu/articles/japanese-beetle/