Japanese beetle

Eric Liskey

Bugs from H-E-double hockey sticks

Written on July 6, 2012 at 10:48 am , by

One of the worst garden pests out there, IMO, is the Japanese beetle. And it’s Japanese beetle season again (sigh). You West Coasters can count yourselves lucky. All of us east of the Plains, buckle up.

In the immature stage, we know them as grubs, the kind that attack your lawn. It’s actually pretty easy to keep them out of your turf. The problem is that the adult beetles are very good fliers, and can travel miles. And they have a seemingly supernatural ability to find the foods they love. So regardless of what you do to prevent them in your own yard, you’ll still have to deal with the hordes that zoom in from surrounding areas.

Contech Japanese beetle trap

There are two things you can do: spray the plants they favor (beans, linden trees, wisteria, hibiscus, and rose, to name a few on a very long list); and use beetle traps. Actually there’s a third thing: many recommend knocking the beetles by hand into a bucket of soapy water. Conceding that the soapy water DOES work on the few dozen or hundred that you might actually succeed in capturing, that still leaves the other 4,568,342,721 to deal with. If you have a mild infestation, you’re lucky, and soapy water might be a viable solution. If you have a bad infestation, well, you know what I’m talkin’ about. Call out the bombers. Or move to another state.

What I’ve started doing is using traps. I know of the research that says they draw in more than they actually catch. But in my case, I’m not so sure. I know this much: when I DON’T use a trap, the beetles do a number on my garden. When I DO use a trap, there’s still a goodly amount of damage, but I think it’s a little less. It certainly isn’t any worse. Meanwhile, as I see it, every beetle in that trap is one less that’s out eating my green beans, and laying eggs for next year’s hatch.

I have used several different traps. They all work. In fact, you would not believe how they pull in beetles! They use a pheromone that gets the beetles in the mood, if you know what I mean. So that would explain why they’re so effective.

It’s what happens after that that sets the traps apart. You see, these things can catch a LOT of beetles. So the capacity of the trap becomes a pretty big deal. But another issue is how easily the trap empties (because they do fill up). And yet another issue is ventilation and drainage holes. Guess what happens when it rains and you get a pile of dead beetles fermenting in warm water of the bottom of a bag? Yeah, it’s as repulsive as it sounds. You better have a cast iron stomach if you want to clean that out without wretching. So…..that’s a problem.

All things considered, the trap I like best is a Contech model. The plastic basket unscrews easily, is vented and drains (not perfectly, but well enough), and it’s heavy enough that it doesn’t flap around in the breeze (which is another thing I don’t like about some other brands). The big problem is its capacity. Often, I come home to an overflowing trap. The other day, I decided to keep emptying it, all day long, to see how many beetles it could capture. And the total was (drumroll, please): 3.4 pounds. Yes, seriously, I weighed it. If the trap could hold a gallon of beetles, it would be the perfect unit. Unfortunately, it only holds about a quart. You can’t have it all, I guess.

3.4 pounds of Japanese beetles -- One day's haul

This all leads to a problem I never considered until I started trapping beetles. What do you do with them all? First you have to kill them. If you don’t, they eventually escape from whatever you hold them in. Usually, a few minutes on hot pavement does the trick if they’re trapped in a bag. Unfortunately, once they’re dead, they stink. Bad. So I have started keeping them in plastic bags on the ground outside our garage (so they don’t smell it up), then I throw them away on trash day. The wife wasn’t real happy about bags of beetles sitting around. She reminded me that our neighbors are trying to sell their house, and bags of dead beetles in the yard next door might be an impediment. Could be she has a point.

But the dilemma remains: what the heck do you do with 20 pounds (a weeks harvest, give or take) of Japanese beetle carcasses? There’s no easy answer.

All I can say is, thank goodness beetle season only lasts a few weeks!


Everyday Gardeners

They’re baaaack!

Written on June 5, 2012 at 11:39 am , by

Roses are one of the favorite foods of Japanese beetles. When one starts to feed, it releases a pheromone that attracts more beetles. Early control is essential to prevent a full-force invasion.

Japanese beetles are back in central Iowa, several weeks ahead of schedule. This morning while photographing in the garden, I noticed (and killed!) half a dozen of the pests on a rose bush, one of their favorite plants. Among the 300 or so other plants that attract them are grapes, hollyhocks, hibiscus, crabapples, and lindens.

Adult beetles usually don’t emerge until late June, but as with everything else garden related this year, they’re well ahead of schedule. Normally the adults feed for several weeks before laying eggs in the ground. We can hope that their early emergence also will result in their early departure! But this means it’s time to start my daily morning rounds of the garden with a bucket of soapy water. I find that’s the simplest and most effective way of controlling them. I hold the bucket under the flower/plant on which they’re feeding, give the bloom a little tap, and the beetles drop into the sudsy solution to their demise.

Avoid the temptation to purchase a Japanese beetle pheromone trap to control the pests. These devices do indeed lure and trap hundreds of the critters, but they also attract many more that never make it into the trap. Instead, the extra beetles feed on the plants in your garden, causing even more damage than had you done nothing.

Japanese beetle trap.


Denny Schrock

Japanese beetle attack

Written on July 22, 2011 at 12:22 pm , by

Japanese beetles feeding on Knock Out rose

Japanese beetles feeding on Knock Out rose

Every morning for the past week and a half, my day has started by making the rounds of the garden in search of Japanese beetles. These voracious pests prefer the roses in my garden, but I’ve also found them on raspberries, hydrangeas, asparagus, and hibiscus. And I’ve seen evidence of their feeding on chokeberries and cannas, too. They can feed on more than 300 species of plants, so they may choose others in your yard. At other locations I’ve seen extensive leaf feeding on grapes, golden rain trees, and  lindens. Most feeding injury occurs on plants in full sun. Damage can quickly mount up because as the beetles feed, they give off a pheromone that attracts other beetles to the site. That’s why you’ll often find clusters of them feeding as on the Knock Out rose pictured above.

Damage to foliage is characterized by leaf skeletonization. The beetles eat the “good stuff” and leave the tough veins behind. Lower on the same rose plant I found the skeletonized leaves pictured below.

Leaf skeletonization from Japanese beetle feeding on rose

Leaf skeletonization from Japanese beetle feeding on rose

Rather than allowing the beetles free reign of the yard, I fight back with a bucket of soapy water. The beetles have the curious habit of dropping off their feeding site when disturbed before flying away. This trait makes it fairly easy to hold a small bucket with several inches of soapy water (I use liquid dish detergent) under the flower or foliage being devoured, and with a light brush of the hand, sweep the beetles into the bucket where they meet a quick demise.

In the grand scheme of things, collecting Japanese beetles every morning during their month-long feeding cycle may not put a noticeable dent in the population (unless you can convince enough of your neighbors to join the attack), but it feels better to be doing something to thwart their actions than to give in to their appetites. And I have to think that eliminating hundreds of hungry beetles at least does a little good. If nothing else, I get the satisfaction of seeing a bucket full of dead beetles!

A morning's harvest of Japanese beetles

A morning's harvest of Japanese beetles

For a list of plants that Japanese beetles tend to avoid, and more control tips, read our online story about Japanese beetle control.


Denny Schrock

Mother’s Day geraniums thwart Japanese beetles

Written on May 7, 2010 at 9:57 am , by

Geranium hanging basket

Millions of geranium (Pelargonium) baskets will be purchased this weekend to honor Mom, and to adorn decks and patios everywhere. Now you have another good reason to purchase these colorful flowers. Researchers at the USDA’s Agricultural Research Service report that the brightly hued petals of this landscape staple are deadly to Japanese beetles. More accurately, after eating geranium petals, the beetles become paralyzed for several hours. In the lab, the beetles recovered after 24 hours, but presumably in nature, paralyzed beetles would be easy pickings for birds or other predators who would devour the pests before they could revive.

Japanese beetle

Researchers provide no indication of how to force feed geraniums to Japanese beetles. However, if your yard has ever been infested with them, you know that the beetles are not picky–they’ll eat hundreds of types of plants. Admittedly, geraniums in the garden won’t likely keep Japanese beetles at bay in your yard, but they certainly can’t hurt. The ultimate goal of the scientists is to develop a natural botanical control for the pests derived from floral extracts of the geranium.

In the meantime, you can buy geraniums for Mom this weekend and know that they’ll be safe from attack by Japanese beetles.