The Identification and Organic Control of Japanese Beetles

Speaking of voracious Japanese beetles, while other beetles eat specific things (like grass roots or other insects) this adult beetle will eat almost anything green in the garden. They'll wolf down fruits, vegetables, flowers as well as any foliage (grass included). These are not your fussy eater.

Important Life Cycle

It is really important to understand a bit of it's life cycle. Only by knowing when it is susceptible to control will your efforts be effective.

The adults emerge just as the summer warms up - normally in the first two weeks of July in a zone 4 garden. These are gorgeous green beetles.

The adults live for 30 to 45 days, feed heavily then the females lay 40 to 60 eggs in the soil. The males simply die off.

These eggs hatch after two weeks and the larvae begin feeding underground on roots. In the fall when the soil temperatures begin to drop, the larvae move deeper into the soil to avoid the frost.

The following spring, they return to the surface where they start feeding again.

In June, the year old grub pupates and the resulting adults hatch out in early July to start the cycle once again.


Japanese beetle

Just because it destroys gardens, doesn't mean this isn't a gorgeous beetle. The thorax (main body) is a bright, metallic green while the wing covers are coppery colored. There are six tufts of white hairs along both sides of the abdomen.

The Japanese beetle is just over ½ inch long.

The grubs on the other hand are an inch long with the characteristics of other white grubs: a brown head capsule, c-shaped, 3 pairs of legs. The distinguishing feature of this grub are the two short rows of spines in a v-shape on the raster and a crescent-shaped anal opening.


Generally, it if kills a June Beetle, it will kill a Japanese Beetle so the organic nematode predators work nicely. There are other methods as well though.

Scented lure traps specifically for Japanese beetles attract the flying adults. The bait is called geraniol, which "turns-on" the adult beetles and has them blindly flying to the lure to quickly become trapped.

I note there are two schools of thought on where to place these traps. Some folks recommend placing them a hundred feet or more away from your own garden so the beetles all leave your area. Other writers disagree and suggest placing them around the edges of your garden. While you'll attract the beetles from the neighbors to your traps, the middle of your yard should be relatively clear of the beetle. This is your call.

Bacillus popilliae – sometimes sold as "Doom" or Milky Spore Disease is available. This naturally occurring product is spread onto the lawn and colonizes the lawn providing a natural and effective grub control.

Follow the label directions to achieve a high population of natural control. This product is not as effective in the South as it is in the North because the heat tends to weaken the bacteria.

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