Battles have been waging across metro area
landscapes and gardens due to significant damage
caused by Japanese Beetles in July. Our mild winter
has resulted in an explosion of beetle populations.
They generally overwinter in turf grass, as a
grub, which pupates in June, and does most of
the damage to ornamental foliage in July. It’s a
coppery green beetle the size of your pinky nail.
It lays eggs in the turf during August and the
grub is back feeding on turf roots until the next
year. If the winter is harder with a longer, deeper
freeze, they can be killed off here in Minnesota.
Warmer winters and natural selection are leading
to higher populations and more damage that has
been in the news.
Plants in the Rosaceae family are favorite tar-
gets — your roses, geraniums and raspberries and
many other ornamental plants. They also attack
trees such as elm and linden and some fruit trees.
What to do? There are several options and it
is not as hopeless as you might feel looking at a
plant crawling with these buggers. First, I would
recommend going to the U of M extension site that
has lots of specific suggestions; everything from
insecticides to picking them off the plant, one by
one — picking is not a bad idea.
Bombs away with an insecticide is still men-
tioned, but not my choice as it is damaging to many
beneficial insects. There are some “insecticides”
that are organic and safer for humans, but again
not necessarily for those beneficials. Some involve
treatment at the grub stage. This is not the timely
help you might be looking for as you watch them
eating away on your favorite ornamental.
One suggestion has been to use Japanese
Beetle traps. These seem to be in two forms: 1)
Sex pheromones that attract the beetles from
great distances to one location — that would be
your garden. Unless you have a big estate that can
sacrifice a corner to the infestation, maybe not so
good to take the hit while your neighbors get the
benefit. 2) Plant traps seem to be another method.
The idea is to offer the beetles a favorite foliage
that you are willing to sacrifice. Question is what
is that favorite. It could be roses, or geraniums or
I have discovered something else this year that I
would like to suggest. It is “kiss me over the garden
gate” Amaranth (Polygonum orientale). This is a
self-seeding annual. I have it every year and it is
perfect for picking the beetles at eye level since
this plant arrives just at the right time at 5-7 feet
tall. All my beetles were on the Amaranth and pick-
ing went from 150 to 25 to 4 to 2 to none over the
span of five days with one stray several days later.
It is a trouble-free plant and you can have it every
year trapping away.