Japanese beetles (Popillia japonica) don't get the publicity they deserve. They're a success story. They can spell Armageddon for some of the most popular plant varieties maintained in backyard gardens, and once entrenched in a neighborhood, are almost impossible to eradicate completely. That doesn't mean you should give up trying, though. Japanese beetles are formidable foes, but they do have their kryptonite. The problem is there are lots of them, and most successful methods for eliminating them take planning. Think of it as warfare. The best campaigns use well-planned strategies that take time and consistent effort to pull off. Once you accept that one bucket of soapy water or a single spray session with a bottle of insecticide isn't going to do it, regardless of your level of gardening skill, it's easier to sign on for the long term fight. Is it painful? Sure. There will be losses. The good news is diligent effort pays off.
They Come from New Jersey?
Don't think you're being targeted by an unfair universe intent on turning your rose bushes into lace doilies. In the U.S. Japanese beetles are so pesky because they have fewer natural predator controls than indigenous species. These pests are Japanese imports (in case you thought the name meant something else), stowaways that made landfall in New Jersey around 1916. In their native land, they aren't nearly the problem they are here. They've been migrating west, gobbling up a smorgasbord of domestic and exotic plant species. Today they're active in 30 states, so at least you're not alone in your frustration and grief over plant losses. JB's are known to feed on at least 275 different plant species, and the annual cost to the turf industry alone is over $460 million. Many of their favorite meals are also popular garden plants.
They like it wet
It isn't all bad news. Weather can have an impact on how active Japanese beetles will be in a given year. They are less abundant during hot, dry summers, and reproduce in fewer numbers, so there's some residual bounty in drought years. The flip side is they love warm, wet weather. If you've had a soggy summer, expect problems again next year if you don't do something to control their numbers.They live underground most of the time
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| Japanese beetle eggs |
By summer's end, it may seem as though you've been battling Japanese beetles forever, but they're actually only active for six to eight weeks. After that, the adults will have laid their eggs and died. Those eggs in your lawn and flowerbeds turn into grubs that will feed on grass and other plant roots over the autumn and winter, and emerge next spring. How much time do they spend in the soil? That would be around 10 months a year.
Mark your calendar
Depending on where you're located, Japanese beetles will surface sometime between Mid-May and mid-July. A good rule of thumb is the farther south you are, the sooner you're landscape is likely to warm up and trigger their appearance. They're pretty predictable, emerging around the same time in an area year after year. If you started seeing them the second week in June, you can plan for next year's assault around the second week in June.