Answer: Sorry you didn't receive my earlier reply. Actually, Japanese beetles don't live in mulch. The grubs live in and usually feed upon grass roots in lawns and meadows, and other places that receive full sun. If you've verified that the grubs have attacked the roots of your raspberries, the landscape fabric should prevent them from reaching the roots. Do the best you can to cover the area, but be careful with mulch. Too much moisture right on top of the raspberry crowns can invite disease.
You can try and prevent beetle damage by covering your canes with fabric row covers before the beetles start to emerge in your area. Your agricultural extension service (ph# 616/336-3265) can tell you when to expect their presence. Best of luck!
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