Japanese Beetle Trap, Part 2

"The Japanese beetle is probably the most devastating pest of urban landscape plants in the eastern United States." Those words from two entomologists at the University of Kentucky aptly describe the impact of these pests that unfortunately have invaded our yard again this year.

About four years ago I described our initial battles with Japanese beetles, and showed a picture of the Spectracide bag system that we employed. After being emptied several times, and being subjected to the winds common in our yard, that bag ripped beyond repair and forced me into a different alternative. I was pleased with the success of the lure and trap idea, but modified the concept as shown below.

The lure is still the Spectracide Bag-A-Bug Japanese Beetle Trap2 Lure which you can see suspended by a 12 gauge insulated wire above the red funnel. The bag has been replaced by a 5-gallon bucket which contains about a gallon of soapy water. This allows me to avoid the steps of dumping the bag into a bucket of water and waiting for the bugs to suffocate. Every day or so I empty the bucket and refill it with soapy water and wait for more beetles to enter and die. Hundreds of beetles accept my invitation each day and enter the bucket to take a swim.

The bucket lid has a 3.5" diameter hole cut in the top and the funnel is simply caulked in place. The funnel end was trimmed back so the smallest portion of the funnel is about 1" in diameter to allow the beetles to more easily enter the bucket. After four years of use I replaced the lid this year as the original Menards lid became brittle and unusable after many hours of exposure to the sun. The bucket itself also cracked at the mounting hole of the handle, but I was able to relocate the handle to a different location so I hope to get more seasons of use from this bucket.

The big question is: does this type of trap attract more beetles than it kills? A quick search around the internet (and reading the article from the Kentucky entomologists quoted above) will show that there are plenty of folks that think these traps are a waste of money and worse for your plants than if you didn't have a trap at all. Spectracide recommends placing your trap 30 feet downwind from the plant of interest, but because our wind comes from lots of different directions, and we have four different plants that attract the beetles, a perfect location on our property would be hard to identify. The image above shows the trap location that has served us well for the last four years. As you can see, none of our plants is less than 30 feet from the lure, and most don't even have a line of sight to the lure. Whether that makes the trap more or less effective, I can't say.

What I can say: the damage due to Japanese beetles on our property is severely reduced by the presence of our trap. Does the lure attract beetles from neighboring properties? Maybe, but if our plants have less damage, I don't really care whose beetles I'm killing. Are there more beetles attacking our plants because I have a lure in my yard? Judging by the damage to the plants, I would conclude that fewer beetles attack our plants since we have less damage when the trap is active.

Tips for best success with a beetle trap

1. Set the trap out early in the season. By the middle of June here in Central Illinois the beetles' damage can be visible from a distance. In my experience, luring the beetles before they can cause extensive damage will reduce the total amount of damage done.

2. Pick beetles off of plants by hand. If you find beetles on your plants, you can easily remove them by grabbing them and tossing them into a bucket of soapy water. I carry my lure bucket to the raspberry plants and hops and have it close by when I physically remove as many bugs as I can. This is easiest to do in the morning or evening as the beetle are much more lethargic and typically don't try to fly away when you grab them. If you find grabbing them unpleasant, you can position your soapy water beneath the branch and shake them into the container. With taller plants like our cherry tree, I simply try to shake the branches to cause the beetles to fly away or drop to the ground. Either way, they're likely to smell the lure and be more attracted to my trap than the tree. The maple tree is too tall, so I make no attempt to remove the beetles from that tree.

3. Remove as many beetles as possible. Several sources indicate these beetles can smell a plant that is being eaten by another beetle, so it's common to see beetles swarm a plant and ignore its neighbor. I have found that if I can remove all the beetles from a plant the beetles are much less likely to come back to that plant. Repeating the process over several days can leave a plant beetle-free for the rest of the summer even though it had been a favorite days before.

I don't have scientific test results that prove our trap is beneficial, rather only my observations. I've seen the damage that beetles can do when left unchecked, and I remember wondering if our cherry tree was going to survive their attack. Since employing our lure bucket, the only time we've had noticeable damage was when I was late setting the trap out and the beetles got a head start on me. I don't have experience dealing with the beetles in the larva stage (other than killing the ones I find when digging in the yard), but I do know the adult beetles can be controlled significantly with a lure trap like mine.

My battles with Japanese beetles

I suspect they've been around for awhile, but I really didn't notice the Japanese beetles in our area until two years ago.  That was when I noticed the leaves at the top of the cherry tree seemed to be turning brown in the middle of summer.  I'd seen other trees suffer that fate, but since they weren't in my yard, I ignored whatever had caused the devastation.  When MY cherry tree seemed to get worse every day, I finally investigated.  I was horrified to find hundreds, perhaps thousands of beetles slowly eating the life out of my tree!

My research that year convinced me to spray the tree with Sevin, especially since all the cherries had been harvested weeks earlier.  It was satisfying to see all the bugs lying dead on the ground just days later, but I realized this war would probably have many battles over many years.

The next year, I noticed the beetles were attracted to several plants in our yard, specifically: the cherry tree, raspberry plants, only one of our three maple trees, and hops bines.  I sprayed all the affected plants except the maple with Sevin, and was generally pleased with the results, but something about spraying chemicals on food plants made me uncomfortable.

This year, I changed my strategy.  I'd seen my neighbors catching a lot of bugs in their traps, and after weighing the pros and cons, I decided to join them.  Of the two or three choices at Menards, I chose the Spectracide Bag-A-Bug Japanese Beetle Trap.  The bait contains a sex attractant and a floral lure that the folks at Spectracide assure me is hard for beetles to resist.

This is the way the product looks assembled and hung from the stairs at the back of our barn.  Notice the plumpness of the bag toward the bottom, indicating lots of beetles are congregating there stupefied and unable to escape.  Evidently these flying beetles are not successful at locating the opening at the top of the bag.  Oh well, that just makes the trapping job easier.

Every day I empty the bag into a 5-gallon bucket containing a gallon or less of soapy water.  This image shows one day's harvest from my one trap after soaking over night.  I haven't counted all of them in this image, but I estimate there are over 1,000 beetles visible, and who knows how many underneath this top layer.  The bugs secrete a brown, sticky liquid that makes the trap bag messy and turns soapy water brown. It also stinks with a potency that is hard to wash off your hands.  I made that mistake once.  Now I use gloves when I'm going to touch the bag so I don't spend the rest of the evening washing stink off my hands!

Because these traps attract Japanese beetles, they shouldn't be located right next to a plant you're trying to protect.  Spectracide recommends at least 30 feet separation, and our trap is about that distance from the cherry and raspberry plants.  Those seem to be protected pretty well this year, although I do occasionally find beetles on both plants.  I remove those bugs when I see them, which tends to prevent others from congregating there also.  One source I read claims the beetles can smell a leaf that is being eaten, so they tend to gather together on the same plants.  Recently, I noticed a few dozen beetles on our small basil plant, and once I removed them I haven't seen any others on the plant since.

Criticized for drawing more beetles to your property, I think this style trap comes out far ahead in removing pests from your plants.  The damage I see on our plants this year is probably comparable to what I saw last year when I sprayed with Sevin at the first sign of infestation.  I'll continue to monitor and empty the trap faithfully, as I'm interested to see if the trap continues to be effective through the rest of the summer.