This is the second villain in our countdown of the Top 10 landscape pests in our area:
Beautifully glowing with green and blue iridescence and
coppery wings, the Japanese Beetle doesn’t look like it should be
despised. But Japanese Beetles have
earned their unsavory reputations by having populations that quickly grow out of
control and damage almost every part of our landscape.
And summer is Japanese Beetle time: this is when the adults
emerge from the ground and start dining on our plantings. With a diet that
includes over 300 different plants, our yards are their buffet. They devour the
soft leaf tissue of our plantings, often leaving only the leaf ribs behind. Since
July is also their time to mate, a few Japanese Beetles can turn into a mob
when they release pheromones that attract other beetles from a mile away or
more.
In late July through August, the females lay their eggs in
our lawns. It takes less than two weeks for the larvae to develop into grubs
and start gnawing their way through the grass roots. These grubs are the single
most damaging lawn pest we have.
There are a few different ways to control Japanese Beetles. Certainly
the simplest is to remove them by hand -- and if the beetles have confined
themselves to a single rosebush, it’s possible to curtail their population this
way. However, if they’re munching through your Birch tree – or you have no
interest in hand-picking beetles – you probably should consider a more
sophisticated solution. We usually recommend applying a low-toxicity spray to
the most susceptible plantings, repeated 2 or 3 times over the course of the
summer.
The grubs represent a different challenge. Because Japanese
Beetles are very mobile, it’s possible to have lots of grubs beneath your lawn,
eating the grass roots and creating dead brown patches, without seeing many
adults. We have several options for treating grubs. When we confirm grub
activity (we do this by lifting the soil and looking), we can apply a grub
treatment. One annual application usually controls all kinds of grubs,
including Japanese Beetles.
There is also a purely organic approach that targets only
Japanese Beetles. Milky disease is
caused by a bacterium that infects Japanese Beetle grubs. We can apply Milky
Spore powder to a lawn to control the Japanese Beetle grub population. The Milky Spore continues to infect the beetles
for several years.
One warning: many sources sell pheromone traps for Japanese
Beetles. These traps work well – at attracting Japanese Beetles to your yard
from all around the neighborhood. So don’t buy these traps – unless they’re a
gift for your neighbor!
