Japanese beetles (Popillia japonica) have become a major pest in Eastern North America and other places. The Japanese beetle trap is routinely recommended for garden use and is easily available commercially, but does it work?
One of the problems with this trap is that it does “seem” to work – it catches lots of beetles. But does it bring all the neighborhood beetles to your yard? Will a Japanese beetle trap reduce the damage this pest does to your roses and other tasty plants?
The answer to these questions is a bit more complex than you might think.
What is a Japanese Beetle Trap?
Commercial traps usually have a yellow top piece attached to some type of bag. A special chemical lure is placed near the top of the trap. Japanese beetles are attracted to the yellow color but the chemical lure is the main reason they come to the trap. Once they get to the trap, they fall in and tend to stay there.
The lure can contain several chemicals. One is a female sex pheromone that attracts males. Another is a chemical that smells like one of their favorite foods, dead flowers, and this attracts both males and females.
If you have ever seen Japanese beetles on your plant, you can guess what happens in the collection bag – a massive sex orgy! 🙂
Does the Japanese Beetle Trap Work?
I always get a chuckle when someone on social media claims “it works”, without ever defining the term. Without a definition, the claim is meaningless.
The trap certainly attracts and captures Japanese beetles but let’s face it, gardeners are not really interested in catching beetles.
They want the trap to protect their plants, so a more important question is, does it prevent damage to plants? If not – it is not working.
Does it reduce the population long term? Will the gardener have fewer pests next year?
How Powerful is the Trap?
Studies have shown that this trap can attract Japanese beetles from as far away as 5 miles (most claim half a mile). This is the reason some suggest that all the trap does is bring in beetles from the whole neighborhood, making the problem worse in your yard.
The reality is that climatic and wind conditions make it unlikely that a trap has such far-reaching effects. Normally they attract beetles from a 250 ft radius. That means that in a normal urban setting, a single trap pulls in all the beetles from the homes you can see from your front and back door.
How Effective Are the Traps?
Research has shown that Japanese beetle traps only trap about 75% of the beetles they attract. The remaining 25% end up near the trap feeding on plants.
The traps ability to protect plants in a garden depends very much on where it is located. When they are within 30 ft of the target plants, the traps do not reduce the damage to plants. In fact, studies show that damage may actually increase when traps are used.
The larvae density in turf is also not affected around traps which means the traps do not reduce the number of future beetles, at least no in your yard.
When traps are placed more than 100 ft away from target plants they can significantly reduce damage to those plants.
Most commercial products recommend placing them 10 ft away from target plants and that is far too close. I suspect they use this recommendation so that they seem suitable for even small backyards.
Spillover Issues are Important
When Japanese beetle traps are used in areas with a lot of beetles, spillover of the traps can become a major issue. This happens when the collection bags get too full and excess beetles are no longer trapped in the bag. In this case, the traps attract beetles to the area which then start feeding on plants.
This can be prevented by frequently emptying of the bags, or by using larger bags. Most commercial products are too small for a high load of beetles.
Some studies have shown success with modified traps that have a very high capacity. In one case the bag was replaced by a 32 gal garbage can, or a four foot long mesh sack.
Low vs High Pest Pressure
In areas where Japanese beetles are well established and numbers are fairly high, the traps are less effective because the reduction in numbers is insignificant compared to the number in the area.
More success has been seen in areas with few beetles, in isolated populations or in areas where the beetle is just starting to establish itself. In such areas, traps can keep populations low enough so that they never get a foothold, and never become a major pest. The traps do need to be deployed over the full area being controlled – not just one backyard.
DIY Japanese Beetle Traps
If there is a commercial product for a pest, there will also be DIY solutions.
A common suggestion to attract the pest is to use water, sugar, a mashed-up banana, and some yeast. This may attract Japanese beetles, but it will also attract all kinds of other insects, including beneficials, but it’s not particularly effective for Japanese beetles. If you are going to make your own traps, at least buy commercial chemical lures which are available as replacement items for traps.
DIY traps may be a good idea. Some traps are quite expensive, and as noted above, most have a bag that is too small. A DIY trap can work when combined with a commercial lure.
Do Geraniums Work?
Lots of online posts suggest that geraniums are a good way to get rid of Japanese beetles. The beetles eat the flowers and leaves, become intoxicated and die. There is some truth to the story which is explained in detail in Do Geraniums Control Japanese Beetles?
Should the Gardener Use Japanese Beetle Traps?
Traps are not very effective in a normal size yard.
They can be useful in two special situations. Traps can protect plants in larger gardens if the traps can be placed far enough away from the plants being protected.
Traps can also be useful where a whole neighborhood uses them. Beetles will not fly into your yard because the traps in other yards are keeping them there. A community using numerous traps can also catch enough beetles to impact the future local population. But this only works if everyone cooperates, and cleans the traps on a regular basis – something many people will not do.
Note: this post contains affiliate links to some products. I don’t endorse these products but merely use the links as examples.
We have a very bird-friendly yard, and that seems to keep their numbers lower. I still get them, and they creep me out, but the robins and starlings love ’em when they are grubs.
I have used Milky Spore in a large, 40+ bed rose garden. Had significant drop in beetles over a several year time period. My understanding with milky spore is that you need to apply 2 times a year, spring and fall for a couple of years. The product actually forms a web under the grass and that prevents the larvae from maturing into a beetle. Milky Spore is costly but it does work, especially in large areas.
Many years ago I applied milky spore to my lawn adjacent to my garden. Haven’t seen much infestation since. Don’t know if that was why, especially since more recent information seems to indicate there exist several particular varieties to control specific pests. I never knew about that— thought it was a generic against all grub types.
Anyway, last year I observed a few Japanese beetles. This year I have seen substantially more, but always on grape leaves. Would expect to see them on my rose leaves, and on zinnias. Have never seen them on a dead flower.
I hand pick with cup of soapy water.
Hello,
How about the use of Btg from Scott’s, do you think it’s worth the try and when should we apply on the grass? Thanks
I tried the traps in my garden in the middle of 160 acres. I only had a few beetles before I set up the traps, had tons of beetles after set up.
IF you have the room, better to allow a ‘trap crop’. Here in the middle of the country in the middle of nowhere, the beetles congregate (and eat) wild grape vine leaves and Virginia Creeper leaves and leave my pole beans, etc. alone. I allowed both the wild grape plants and Virginia Creeper to vine on the fence separating my garden from the pasture. By the end of the beetle season, the wild grape leaves and the Virginia Creeper leaves are nothing but lace and the beans (and other vegetable crops) have no damage.
This might not work in the city (vines on everything) but it sure works here.
Neem oil helps too. It is organically acceptable. Can use on flowers or veggies.
It doesn’t kill them outright, you are not going to see piles of dead beetles, but it affects their nervous (?) system and they forget to eat and mate.
One other thing I didn’t like about the beetle traps, when my windows were open on the South side of the house and there was a breeze from the South, I could smell what ever ‘bait’ is in the traps in my house, 300′ away.
Skip the traps, let some wild grapes or Virginia Creeper take hold or if you can’t do that, use Neem oil.
“But this only works if everyone cooperates, and cleans the traps on a regular basis – something many people will not do.” if all the traps had 4 foot bags on them they wouldn’t need to be cleaned. Maybe a garden group could do their area by getting local school children to put up the traps in their back yards.
What pesticides do you recommend?
Dear Robert,
What are your recommendations on hlw to fight the pest in the home garden? If trappung does not really help, what would be a better method?
Roland
Hand picking and drop them in soapy water.
We have seen in past years that when the Japanese beetles attack our grape vines, the sparrows fly in and eat them! I also hand pick them from my flowers that attract the beetles. So far this year, I’ve seen the damage but very few beetles. Those I’ve seen, I pick off. Maybe the sparrows have been there before I get to them!
Judy Stewart
Very interesting! I joke about putting the trap down the road to keep them off my garden. I used milky spore a few years ago, it seems to have helped in that I didn’t have swarms on my gardens anymore but lately I’ve been seeing a handful. I also noticed the soil in my raised beds, which is bagged soil, had some grubs in it. I’ve read milky spore can last up to 20 years. If that’s true, rather than knocking these into a bucket of soapy water, would it be just as helpful to let them drop to the ground that has been treated?
1) I don’t know how effective milky spore is – is it 100%? soapy water is 100% effective.
2) Once they hit the ground they may go somewhere else to lay eggs, that has not been treated with milky spore.
Actually, yeas soapy water is bound to work but I’ve also dropped a bunch in a bucket of water, and by the next morning they were still all there. I have a horticulturalist friend who does not believe in the traps, he tours his garden daily and collect them. Myself I do both and I am happy with the traps.