My first affair with the metallic green, oddly pretty, but nasty Japanese Beetles was during my first job in Chicago. The company I worked for – an extraordinary place – managed a gigantic, gated community. It was late June and I was checking some plantings when I started to get hit with something. Couldn’t figure out what was going on until I looked up and an enormous swarm of Japanese Beetles had completely engulfed a 50′ Linden.

The tree was toast, but I was more worried about myself. Japanese beetles have a tendency to get aggressive toward the color white. I was wearing a white shirt.

Hated them ever since.

Life cycle

So our friend, the Japanese Beetle’s life cycle with two main stages: grub and adult.

The larvae live in the soil and cause significant damage to turf. The grubs mature to adults and pop out of the ground May – July. The adults dig back into the soil and lay eggs. The egg hatch into grubs August/September and dig deep to overwinter. They come back up to within 4″ of the surface when the weather turns nice, eat all your happy grass roots then mature to adults and the cycle starts over.

http://www.extension.umn.edu/distribution/horticulture/dg7664.html

Damage

japanese beetle on rose

Adults feeding on rose blossom. Notice leaf damage in background.

The adults eat the tissue between the veins of the leaves of many different plants:

  • Linden Trees
  • Roses
  • Grapes
  • Crabapple Trees
  • Mountain Ash and others

A few Japanese Beetles is not a problem, but when they find a plant they like, they emit a hormone attracting the masses. The beetles swarm a plant and begin devouring the green leaves from top to bottom. If they are really out in force, you can be left with a majority if your leaves, flowers and buds completely gone.

Japanese Beetle Grub

Ugly Japanese Beetle Grub

The grubs leave brown patches in your turf that can easily be picked up by hand or scratching with your shoe because the grubs eat all of the roots. When you peel back the turf you’ll see the grubs curled into the letter C then you can smash it.

Controls

The adults are pretty easy to kill with a spray. Kill the buggers as early as you can to keep them from laying eggs. However, the adults don’t all emerge at one time, they kindly do that over the course of 3-4 weeks so we need multiple treatments.

The grubs are killed with a broadcast granular treatment of insecticide. Do not blanket treat an area, even if there are adults in the area, it doesn’t mean that is where they were in grub stage. Locate damage in turf and find the grubs, then treat that area.

Another alternative has been marginally effective in controlling grubs. Milky Spore is a bacterial biological control. The grubs eat it, the bacteria multiplies and kills the grub then introducing the bacteria back into the soil for the next hungry grub. It has worked in other regions, but midwest trials have not been as successful for unknown reasons.

Resources

University of Minnesota Extension

MN DNR JB Page

Entomological (I made that word up) Info

The effect of the social environment on post-copulatory mate guarding duration in Japanese beetles (I couldn’t not put this one in here)