The Lifecycle, Identification and Methods of Controlling Japanese Beetles
Adults consume fruits, vegetables as well as foliage plants such as grass – green and leafy is good!. The larvae are just as hungry, they'll eat anything including the tender feeder roots of many plant families.
If you have beetle damage, expect to see the typical yellowing patchy lawn in August and September followed by dead turf shortly afterwards.
Interestingly enough, this is not a major pest in its native Japan where predators restrict its population.
Much of the Northeast United States and Canada is a target for this pest because of climate similarities and a lack of predators.
Emerge In Summer
The adult beetles usually emerge just as the summer starts to heat up - normally around the first two weeks of July in my zone 4 gardens.
The adults live for 30 to 45 days and feed heavily and the females lay between 40 to 60 eggs in the soil.
Eggs Hatch In 2 Weeks
These eggs hatch after two weeks and begin feeding underground.
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 second year grub pupates and the resulting adults hatch out in early July to start the cycle once again.
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 beetle is just over ½ inch long.
The grubs on the other hand get to about an inch long with the same characteristics of other white grubs: a brown head capsule, c-shaped, 3 pairs of legs. The distinguishing feature of this grub are two short rows of spines in a v-shape on the raster and a crescent-shaped anal opening. (OK – everybody get out their magnifying glasses!)
Generally, it if kills a June Beetle, it will kill a Japanese Beetle. There are other methods as well though. Scented lure trapsspecifically for Japanese beetles catch adults. The bait is a substance called geraniol, which turns on the adult beetles (sex-craxed adult beetles – now there's a concept!) flying to the lure and becoming trapped. However, never install one of these in your own yard as you'll have every Japanese Beetle for miles around flying in to find a hot date. Put it at least a hundred yards away.
Also, a product that creates Milky Spore Disease in grubs (Bacillus popilliae – sometimes sold as “Doom”) is available. This naturally occurring product is spread onto the lawn and colonizes the lawn providing a natural and effective grub control. Do follow the label directions to ensure a high population of natural control. Note that this product is not as effective in the South as it is in the North.
Here's more information on controlling white grubs
As a final thought, you'll be able to identify Japanese beetles when you see the gorgeous adults eating your garden. Once you identify the adults, work on control for them and their grubs.
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