Everyday Gardener: Some things to know about Japanese beetles

For five years now I’ve fussed over bare-root sprigs and cuttings of Virginia creeper, nursing them into the lush vines that now cover three arbors and a couple of fences at my house. This week, I started ripping all those vines out because, sadly, Japanese beetles just love Virginia creeper. For a while, my husband and I thought we could live with the damage the beetles do —all those green leaves reduced to lacey brown ghosts of their former selves. But when scads of beetles and showers of the dust-like poo they leave behind started raining down from the arbor into our hair every time we shut the back gate, well, goodbye vines.

For those who aren’t familiar with Japanese beetles, they are actually quite fetching little bugs. Dime-sized with shiny purple-green bodies, they almost look like something a wacked-out artificial intelligence researcher would create in a sci-fi film. First spotted in 1968 in Minnesota, as well as on the East Coast, Japanese beetles have since plagued eastern states, primarily, while slowly making their way westward. Larvae, or grubs as they’re usually called, feed on the roots of turf grass and adult beetles feed on a wide variety of ornamental plants.

With the exception of a brief time in 2000 and 2001, the beetles weren’t much of a problem here until 2005. That’s when the University of Minnesota Extension Service noticed a sizable increase in calls and e-mails from homeowners asking about the strange, metallic-looking beetles devouring their plants. Japanese beetle populations have continued to grow ever since. And Jeff Hahn, an Extension Service entomologist, tells me he thinks 2011 may be the worst year for them yet.

My non-scientific sense is, he’s absolutely right. Last year, I trapped a Japanese beetle in a jar in my backyard so I could use it to show homeowners when I gave master gardener presentations. This year, I could have filled at least half of a five-gallon bucket with the beetles I’ve picked off plants and drowned in soapy water since late June. Eating supper at night on our back patio, I swear the Virginia creeper on the garage is black with a thick layer of beetles engaged in such an orgy, you feel like you ought to look away.

Understanding the enemy

Japanese beetles cause a lot of unsightly damage to plants and turf, but they rarely kill anything unless the plant was very young or unhealthy to start with. Knowing this, you’d think we could cut them some slack. But, no, we can’t. The reason? They’re gross (see poo reference above for starters). It’s not their fault, really. They have to pack a lot into their short life cycles, so once the adults emerge from the soil at the end of June or early July, they have to eat, poo and make a lot of babies in pretty short order. Adults only live about 60 days and are pretty much gone by September.

As you’ve no doubt noticed, Japanese beetles like to feed in full sun, but they’ll settle for shade if there’s something planted there that they like. (Go to this USDA website and download the homeowners’ handbook for a list of plants to avoid if you want to discourage Japanese beetles: aphis.usda.gov/plant_health/plant_pest_info/jb/index.shtml.) The beetles start by feeding at the top of plants and move down. I thought it was my imagination that heavily infested plants smelled terrible but, in fact, I read an Extension publication that explained how leaves damaged by the beetles do emit an odor that attracts more to the party.

Worse yet, adults also release pheromones that attract even more beetles. These pheromones dissipate by dusk, which would seem like a great thing if it weren’t for the fact that that’s when the females fly over to the nearest turf grass to burrow a couple of inches into the soil and lay more eggs. Grubs hatch by late September and move as few as two but as many as 10 inches into the soil for the winter before starting to feed on grass roots again once the soil warms up in May. So their life cycle is egg, grub, adult, and this is important to know when you’re considering how to kill them.

Possible murder weapons — stay away from traps

At a time when we are losing more and more beneficial insects and pollinators to environmental problems; chemicals, such as pesticides and herbicides; and problems like colony collapse, the Extension service cautions against using chemicals to kill Japanese beetles. Instead, for those who have reasonable-sized gardens, they recommend knocking the beetles off plants into a bucket of soapy water. (Wear gloves—my recommendation, yuck.) In my experience, these beetles are so engrossed in eating and making out, they’re surprisingly easy to brush into the water. And none of them seem to send out any kind of alarm to their comrades, so it’s just plop, plop, plop.

For those who find this just too much, have enormous gardens or are growing some of the beetles’ favorite things (grapes, roses, apples, raspberries, cherries, walnuts) for food or to pay the mortgage, there are several pesticides to choose from. Some work on grubs, others work on adults. Timing of the treatment of grubs is crucial because you have to get the grubs when they’re in the soil and have not yet emerged as adults. Treatment options are outlined in this Extension publication: www3.extension.umn.edu/distribution/horticulture/DG7664.html. (Tip: milky spore isn’t working.)

One thing to know before you decide to treat the grubs, Japanese beetles can fly miles to get to a plant they like, so you can’t be sure you have them in your turf just because you see them in your garden. The Extension publication covers how to locate and identify the grubs before you apply chemicals. You have to ask what’s less repugnant, right? Would you rather dig up grubs and examine them closely or knock the little buggers into a bucket? And even if you treat your yard, if all the lawns around aren’t treated, the beetles will still be a problem. That’s another reason the University and others across the country are suggesting we get out our soap buckets rather than pesticides.

For adults, Jeff Hahn suggests neem or pyrethrins, as lower-impact choices but they have to be applied often and can harm beneficial insects. Neonicotinoid insecticides are the big guns. They are longer lasting, but they kill bees like crazy and shouldn’t be used on any plants that attract bees, including linden trees. As always, read the label before using any chemical, particularly when it comes to food crops. If the chemical you’re using doesn’t list the food crop you have on the label, don’t apply it. Never spray chemicals when bees are around, and don’t spray on a windy day.

This is probably more than you ever wanted to know about Japanese beetles. I sure wish we didn’t have to know about them. But since they’re settled in now, we have to learn to cope and make our own decisions about what we’re going to do. I’m going with the bucket of soapy water and removing the plants they like from my garden.

Meleah Maynard is a writer and Master Gardener. Her Everyday Gardener column appears monthly in the Southwest Journal.