Jim Dill Pest Management Specialist
Hi, I’m Jim Dill. I’m the pest management specialist with the University of Maine Cooperative
Extension and I want to talk to you a bit about Japanese beetles. Here in the state
of Maine, depending on where you live and weather conditions, Japanese beetles start
coming out at the end of June. Give or take a week on either side of that, and you’re
going to be able to look outside and find Japanese beetles just about everywhere.
What we want to do first is talk a little bit about the biology. When the adults come
out sometime around the end of June or beginning of July, the first thing they do is look for
a food source. Once they start feeding on the food source, their priority is finding
a mate. When they find one, they begin mating and lay their eggs about 10 days later.
In most parts of the state, the Japanese beetle is laying eggs in the turf by the middle or
end of July. The larvae hatch a couple weeks later, so by about the middle of August you’ve
got larvae feeding on the roots of your grass. When we talk about management, there are two
different strategies to work with. One is controlling the adults, and the other is to
deal with the larvae. One of the things I suggest is to fill a container with water
and put in a little dish washing liquid. Once you’ve got a few drops in, it breaks the
water’s surface tension so the beetles fall in and drown. Then all you do is place the
bucket underneath the plant and start tapping. Yes, a lot of them will fly away – that’s
just the nature of them. The next method of controlling them works
great, especially if you have kids. For some reason, kids just love to get out there with
a regular old car vacuum or hand vacuum. Just charge it up and vacuum up the beetles. Admittedly,
once you’ve done this, you probably want to dedicate the vacuum to doing this, because
it gets a little messy inside. Once you’ve vacuumed them up, you’ve got them trapped
in there, so you open it, dump it into soapy water and the adults drown.
There are several organic materials available to the homeowner, including spray pesticides
that work quite well. A couple of them contain some type of insecticidal soap, which actually
smothers the adult beetles. You can also use something containing Neem, which is an anti-feedant
– it prevents the beetles from feeding. Once you spray it on, they will stop feeding
and eventually leave the plant alone and die due to its toxic effects.
I’d be remiss if I didn’t talk about this last thing, and that is Japanese beetle traps.
Everybody asks, “Should I use Japanese beetle traps?” Of course, the big joke is, “Yeah,
give them to your neighbor, put them in his or her yard and all the beetles go over there.”
Well, that’s not so far from the truth. What happens is there are three things that
act when you’ve got a Japanese beetle trap. You’ve got the bright yellow color, and
then there are two different lures we put in there. One is a pheromone lure that attracts
just the males, and the other one’s a floral lure that attracts both males and females.
So they go to fly into the trap, but they’re not the best flyers in the world. They’re
good, but they’re not the best at landings. So if your trap is sitting in your rose bush,
they go flying into it but miss and get all over the roses.
So even though your Japanese beetle trap will be great, will work and will just be full
of beetles, you want to take a stake and put your trap at least 50 feet away from what
you’re trying to protect. As I said, the Japanese beetles come out here in Maine sometime
around the end of June, start mating and lay their eggs sometime from the middle of July
until the end of July. What they look for is a nice grassy area. The females go down
and lay their eggs, and within 10 days, depending on the weather and the temperature, those
eggs hatch. As soon as they hatch, the first thing they
start doing is feeding on the roots of the plant. If you want to try to control these
stages of the Japanese beetle and don’t mind using a synthetic insecticide, there
are two or three of those available on the market that can be used quite effectively.
If you want to try to do it organically, the only thing that really seems to help here
in the state of Maine is using nematodes. We use what we call the HB nematode. You can
call your local extension folks and they can tell you about it, or you can go online and
Google it. The HB stands for the scientific name, which is 20 syllables long or so, but
all you need to say is HB nematode and it will come up. A lot of the time they come
in a little sponge. You soak that for an hour, put the nematodes in a watering can, spray
it out over 5,000 square feet and then those nematodes attack the grubs.
Whether you’re going to use nematodes or some type of synthetic chemical in your lawn,
the time to do that is from the middle of August until the beginning of September. That
way, you’ll get most of the more complex grubs, because there are other things aside
from the Japanese beetle out there that will be hatched and susceptible at that stage.
Of course, the last option you have is to call in a professional certified pesticide
applicator who can come in and treat your lawn or shrubs.