by Connie Oswald Stofko
It’s the time of year when Western New York gardeners may be finding Japanese beetles in their gardens.
If you have Japanese beetles, you will see them; they’re easy to spot. About half an inch long, they’re big enough to see, plus their coloration catches your eye. They are green and copper, and they’re shiney.
The damage they do may catch your eye as well. They feed on rose petals— and on about 300 other kinds of plants, according to Elizabeth Lamb, Ornamentals IPM Coordinator at New York State Integrated Pest Management.
Lamb explained how to manage Japanese beetles in a wonderful online talk last week in the What’s Bugging You First Friday series. Tip: Watch our Events page for this series and other events that you may find helpful. If you missed Lamb’s talk, don’t worry; you can see the entire talk here.
How to manage adult Japanese beetles
What you see now in your garden are the adults.
Handpicking
The best way to manage the adult Japanese beetles is to handpick them. They aren’t slimy, so picking them isn’t as disgusting as other insects, Lamb said. Drop them into soapy water and they drown relatively quickly.
If you see a great big group of Japanese beetles you may have to put your hand over the top of the leaf that they’re on to catch them all. If you don’t catch them, they will fly away, but they’ll often come back.
Vacuum
Lamb has seen people use a vacuum cleaner to scoop up the beetles. You might want to use a small hand vac. However, you have to kill the beetles once they’re in the bag or leave them there until they die.
Japanese beetle traps
These traps may attract more beetles than they catch, Lamb said.
The trap has a pheromone that lures in the Japanese beetles. The beetles can smell the scent from a long distance, so you may be attracting more beetles into your yard than are already there, she said. In addition, the trap captures only about 75 percent of the beetles that are around the trap.
If you’re going to use these traps, don’t put them near any plant that you want to protect, she suggested. You might also place the traps at the edges of your yard to try and catch the Japanese beetles before they come in.
Biological controls
Some biological controls are being tried. One example is the winsome fly, which lays its eggs on the adult Japanese beetle. That kills the adult in six or seven days, which is pretty fast for a biological control, Lamb said. It is hoped that the winsome fly spreads.
She said she will be looking for any Japanese beetles with the little white eggs on it. If she finds one, she will let that beetle go so that the winsome fly eggs hatch out and start a new generation of winsome flies that can lower the population of Japanese beetles.
Chemical control: NO!
Don’t use chemical pesticides to try to control adult Japanese beetles.
“The adults will keep flying in,” Lamb said, “so you can apply a chemical pesticide, but it’s not going to protect your plants from the next group flying in.”
In addition, it’s difficult to read pesticide labels to know what to use and how to use.
Definitely don’t use chemical pesticides on food plants, she said.
Japanese beetle grubs
The larvae of Japanese beetles, also called grubs, live underground and can cause damage to your lawn. You usually find brown spots where the grubs are feeding.
If you have brown spots, dig down three inches to see if you have grubs. Or you can dig up a square meter (or square yard) of lawn, and if you have 10 grubs or more, you should treat, Lamb said.
There are good biological controls for the grubs, which you can see on the video at the 10:45 mark.
Milky spore and beneficial nematodes called Heterorhabditis bacteriophora are two biological controls for Japanese beetle grubs that are available at Urban Roots Cooperative Garden Market, 428 Rhode Island St., Buffalo.
You can do the grub management in early fall when grubs are small and feeding.
However, Lamb noted, killing grubs won’t prevent adult Japanese beetles from flying in from other areas.
Hi Suzanne, thanks for the tip on not filling the jar all the way up!
In my Orleans Co yard, Japanese beetles love our roses and raspberries. My method of dealing with them is to make a concoction of Dawn detergent and water in a wide mouth jar and knock them into it. Don’t fill the jar with liquid or they’ll crawl out; an inch or two works for me.
Hi John, yes, they really work on the grubs!
We’ve had great luck with Beneficial Nematodes in North Tonawanda
Hi Marge, a gardener once told me that he bought several Japanese beetle traps and gave them as gifts to his neighbors. I think he was joking.
Hi Meredith, thanks for that suggestion!
Hi Terry, if you try vacuuming, let us know how well it works. Nice to hear from you!
Hi Patricia, the beneficial nematodes will kill the grubs, so they won’t grow to be adult Japanese beetles. Unfortunately, the adult Japanese beetles may fly in from elsewhere. I had only a few adult Japanese beetles this year–the first time I had any in probably 20 years–and my grandchildren would catch and squish them. I’m glad it works for you.
Hi Sue, thanks for the comment. It’s probably best not to use neem oil on open flowers. It may have killed Japanese beetles, but it may have killed bees and other pollinators, too. Check out my previous comment about neem. Thanks!
Hi Marlene, yes, neem oil kills bees. It kills any type of insect. It is a pesticide. Neem oil is made from plants, so it’s organic, but it is still a pesticide and kills insects. See more here. Thanks for this question!
Last year, I sprayed my garden beds and grass surrounding with beneficial nematodes and I feel like I did have a reduced Japanese Beetle problem. This year, I didn’t do that and I’m regretting it, because they are plentiful. They’ll eat an entire freshly bloomed or not even bloomed rose in minutes. This year, and unlike years previous, they’ve also gone after my basil plants – another frustration. I just squish them now, it helps me let out some of that anger that my poor plants are being destroyed.
Vacuuming! Love that idea. I hate picking them. I have sprayed them with soapy water, which seems to work, but then it is a timing issue to let the soap kill them, but rinse off before it harms the plant.
Does Neem Oil harm the bees?
Thanks for the info on the winsome fly – I’ll be sure to check the beetles before I feed them to the bass in our pond. We stopped using traps a couple of years ago and noticed a big decline in the amount of beetles we’re seeing. This season they gathered mostly on zinnias at first and now I see them on blueberries, raspberries and other plants. My husband sprayed Neem oil on the zinnias and it seemed to deter the beetles for a couple of days. Thanks again for the info, Connie!
Hi, not saying I like them but compared to other pests they seem easy to spot and deal with! Two weeks ago my ferns were inundated but I picked them off several times a day and few remain anywhere in my yard. I would say that early control is the best way to go.
Very helpful comments! We did not put out the Japanese Beetle traps this year and noticed not as many in our yard and on our plants.