Japanese Beetles are very destructive. You will want to get rid of them from your garden. They feed on more than 300 species of plants from grape vines to roses, corkscrew hazel to lindens and their grubs will eat the roots of your turf.
You won’t see them early in the season but as the weathergets hotter they will start to appear on your plants.
Know your Enemy
First you have to be able to recognize them. Japanese beetles are about half-an-inch long, metallic green with bronze wing covers. A series of six white tufts run along each side of their bodies.
This is the kind of damage that you will see. The leaves have been skeletonized, as can be seen from the photo attached to this article.
Why are there More Japanese Beetles?
It may be due to Ontario’s ban on pesticides, which ended the use of products that kill grubs in lawns. It may also be because when we are on the up-curve of the natural insect cycle of beetles, the numbers increase. When we are on the down cycle, they are likely to decline in number.
Controlling Beetles
Walk your Garden
The first line of defence is to walk your garden every day or as often as possible. The beetles are less active in the early evening and so are easier to catch. Go armed with a jar of soapy water and carefully pick the beetles off your plants and drop them into the soapy water as this will kill them. If you are squeamish about touching the beetles wear disposable gloves. (You can buy boxes from drug stores.) The beetles will fly away when they feel the flower or leaf move so be swift and accurate. You will be amazed at how many can fit on one flower. When there are lots on one flower or leaf, remove the flower and beetles in one go. This prevents some from escaping.
Don’t Use Traps
Many people ask if they should use traps. This is not necessarily a good idea. The traps contain phenomes that attract beetles. This means that you will not only get the beetles that come to your garden but also those of your neighbours as the phenomes attract all Japanese beetles in the area.
Insecticides
If you have too many beetles to kill by hand you will need to think about alternative measures. You can talk to staff at your local garden centre to find out what you can use. Master Gardeners always prefer environmentally friendly products so do your best to find something that will not harm beneficial insects.
Many insecticides e.g. carbaryl, bifenthrin, pyrethrin, imidacloprid, permethrin and more will kill the beetles.
References and Resources for more information
Canadian Food Inspection Agency fact sheet
OMAFRA fact sheet, Grubs in Lawns
http://www.omafra.gov.on.ca/english/crops/facts/08-023w.htm
North Dakota State University Extension
https://www.ag.ndsu.edu/yardandgardenreport/documents/japanese-beetle-alert
Michael Fox, Garden Making, How to prevent(okay, reduce) next year’s Japanese beetles:https://gardenmaking.com/how-to-reduce-japanese-beetles/
Submitted by Chris Harwood