Going Ninja on Japanese Beetles

The Mountain Xpress
August 2, 2006

updated 2023

First one or two metallic green and copper beetles here and there, then suddenly, hundreds of munch-tanks on your prize rose bush or peach tree, devouring petals and turning green leaves to brown skeletons. Ladies and gentlemen, without no doubt, these are the JB’s!

When I first discovered Japanese beetles on my grape arbor in July, there must have been at least three hundred of them. Within a couple of days, I had gotten the population down to about twenty-five, plus a few more scattered about the yard. Here’s how I did it — without any poison.

Japanese beetles can start showing up as early as late May and last until September, but their peak activity only lasts four to six weeks. If you have a concentrated infestation of JB’s on a single tree, trellis, etc. and a few minutes to spare each morning and evening, then my advice should work well.

The prevailing wisdom says that the best way to deal with Japanese beetles in the short term is to gather them up by hand, and I have to concur. Granted, for those of us over the age of eight, handling insects can be a bit unnerving (to find out, put a few beetles in your hand and let them try to push their way down between your fingers). The good news is that one, they don’t bite; and two, to catch them, you rarely have to actually touch them. You can even use a hand-held vacuum cleaner, but that sort of spoils the fun.

Think of stalking these space invaders as a game, like you’re some kind of neo-ninja, and it won’t seem tedious. If the thrill of the hunt pales after a few days, then do as garden guru Walter Reeves suggests and find a child to do it. “At a nickel per bug, a trip to the ice cream store can soon be financed!”

The problem with beetle traps you can buy in the store is that they can indeed trap thousands of beetles a day. However, they always attract more beetles to your yard than they actually catch. The only effective way to use such a trap, then, is to place it a few hundred yards away, i.e., in someone else’s yard. Obviously, using traps requires some neighborly cooperation, something that nowadays is hard to come by.

It is possible to make your own trap, perhaps a weaker one with a shorter range. There are also a number of “trap crops,” i.e., plants (including weeds) that JB’s love. You just pick the beetles off the trap plant. The problem once again is that you may attract more beetles than you catch. It’s best, then, whenever possible, to avoid or remove plants the beetles like. These include smartweed, Virginia creeper, wild rose, evening primrose, and wild grape. You can find a list of others online, or just find out the hard way.

There are a number of plants which attract JB’s but poison them as well, kind of like humans and sugar. These floral fatales include four o’clocks, larkspur, white geranium, red or dwarf buckeye, and castor bean. Assuming these trap crops don’t also attract more beetles than they kill, you might consider planting them for next year. Keep in mind, however, that they are poisonous to children and pets as well.

There are other methods: attracting birds, many of which love to eat JB’s, introducing parasitic insects and diseases, and simply covering smaller plants with netting. These approaches were either too involved or just not feasible for my needs.

I did try the biodynamic, that’ll-teach-’em method of putting some of them with some water in a blender and spraying that on the plants. I certainly found it repulsive, but even with habanero oil and tobacco added, it didn’t seem to phase them. Fortunately, simply gathering them every morning was enough – and not a bad way to get out of the house and keep tabs on my garden as well.

You’ll notice that JB’s start from the top of a plant and work their way down. They’re also attracted to already-damaged plants, so removing damaged leaves can help. But that’s a lot of leaves to remove! That leaves removing the culprits themselves.

The cardinal principle of JB-hunting is that the early gardener gets the beetle. In the morning, Japanese beetles are either too cold or too wet to fly. Evenings work too, but not as well. It’s said that the beetles won’t fly in the heat of the day either, but that’s not my experience.

The trick to catching JB’s without even having to grab them is that, when they sense danger, they drop off the plant. They tumble down to the ground, where they are usually very hard to find. Your mission, then, should you choose to accept it, is to intercept them in between.

In theory, you could spread a sheet or tarp on the ground around the plant. Then you just ‘shake and rake,’ gathering up the pickins like mulberries, only crunchier. But in a crowded garden like mine, this is impossible. Besides, as the day warms up, JB’s often fly off. You would hope they would just land somewhere else. But this NIMBY approach can merely spread them to other plants in your yard, where they will make doilies out of your dahlias if you’re not patrolling daily.

The best approach I have found is to hold a quart-size yogurt container beneath them with one hand, then gently brush them with the other. Beetles that have dug themselves into the center of roses or other flowers may need to be coaxed out.

Always look carefully before you reach for a bug. You don’t want to shake the plant and cause the rest to scatter. There are bound to be more, maybe even on the underside of the same leaf. And this is the secret to why they stay in the container.

If you haven’t already noticed, JB’s are awfully “social.” They can smell each other’s parfum sexuel hundreds of yards away, and they don’t hesitate to join the party. That’s great for us: it makes them easier to find, and the more you get rid of, the fewer come. Your work has a cumulative effect.

In your container, the converse is true: the more you add, the less likely they are to get out. It’s as if they become unable to decide, “should I stay or should I go?” They clump together increasingly until they’re one writhing mass, and it’s not clear whether they’re climbing all over each other to escape or to mate.

I have a theory that, in excitation, whether sex or fear, JB’s release the same pheromone. Either way, it looks exactly like a Hieronymus Bosch painting of hell. There must be something to learn from this.

Now what do you do with them? Most prefer to drop them into a container of soapy water (they’re not good swimmers). Or you could just stick the container in the freezer. You can put the vanquished throng out for the birds, feed them to fish or chickens, or do some kind of art project with them. I feed them to other people.

JB’s taste like peanuts; simply toast them to kill any possible parasites. Here they are, straight out of my yard, the coup de gross at a $800 dinner prepared by Mads Refslund, co-founder of Noma, four times voted the #1 restaurant in the world.

So that’s the “crouching tiger, hidden beetle” method of JB management. Remember to look at it as fun, at least on your end. Isn’t that a good approach to life?

Malcare WordPress Security