Everyday Gardeners

Plant. Grow. Live.

Garden warfare

Japanese beetles are one of the most notorious garden pests. They begin as grubs—a significant turf pest in the Eastern U.S.—then turn into those little green beetles we see flying around in summer,  chewing up our roses, hibiscus, beans, etc. The list of victims is a long one. Japanese beetles are such a serious pest, the species is on those “shoot-on-site” lists that ag-intensive states such as California maintain. Just like the Medfly (those of you on the West Coast know what I’m talking about), if a Japanese beetle is detected in California, they call out the bombers.

Japanese beetles -- eating and, um, engaging in a certain activity with Darwinian implications.

Japanese beetles doing the two things they're best at—eating and multiplying .

East of the Rockies, however, the beetle has spread widely, covering pretty much every state. In some places I’ve visited (on the Eastern Seaboard), I’ve seen the beasts so thick, they attack roses like flies on a rotten piece of meat. Seriously. Swarms. They’re usually not quite that bad here in Iowa, but it’s been heavier this year than I’ve ever seen it before. I blame it on the heavy snows that insulated the ground here all winter.

It’s been bad enough that, for the first time, I felt the need to do something about it. I first tried a homemade trap. “Works Great!” the message boards said. Mash up some fruit, add sugar, water, and put it in a milk jug. So….a few days later I went out to inspect my catch: 1 cucumber beetle and a mason bee. No Japanese beetles. Meanwhile, a few feet away, a bean vine was covered with them.

So I bought one of the commercial traps—this one manufactured by Bonide—that uses pheromones to lure in the beetles.  A couple days later, the bag was  full of hundreds of the nasty little things. It worked! It’s pretty disgusting to see a bag full of writhing bugs. At some point, you have to get rid of the things. What do you do with them? I haven’t figured that out yet. They’re still in the bag.

A commercial, pheromone-based trap. It works!

A commercial, pheromone-based trap. It works!

It is satisfying to see such a great result, although the truth is, you’ll never eliminate Japanese beetles. The key is grub control. Not so tough in your own yard, but there are always plenty of untreated lawns nearby. Given their excellent flying ability, the adult beetles can and do converge on any attractive food source anywhere close enough to fly to. So you might keep the populations down with a trap or other control, but the reality is that you just have to tolerate a certain amount of damage.

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