The Evil Japanese Beetle
This nasty new visitor to Iowa devours roses, fruits, lawns, and just about anything else that gets in its path. Here's how to carve out a peaceful co-existence.
By Veronica Lorson Fowler
The Iowa Gardener
It used to be that we heard about Japanese beetles only from eastern gardeners. It arrived in New Jersey in 1916 from Japan and has spread. But until about 1994, this garden pest wasn't found much west of the Mississippi.
Its concentrations are worst in the east central part of the state, but it's definitely a pest in my Ames garden here in central Iowa.
What They Are
Japansese beetles are actually quite beautiful insects, about a half-inch long with a head and thorax that are a shiny metallic green and coppery red wings. (I often thought they'd make a beautiful pin to wear on a sweater or lapel.)
The adult beetles start munching plants in mid-June through July. The larvae--grubs--eat turf roots, damaging lawns.
There are many different sorts of white grubs that live under our lawns. Japanese beetle grubs are C-shaped and about 1 ¼ inch long. The damage they do shows up in August and September.
What They Destroy
These hungry adults eat more than 300 plants, and their favorite part by far is the flowers and fruits. But they also leave behind skeletonized leaves and large irregular holes in leaves.
Probably their all-time favorite plants are roses, especially hybrid tea roses.
How to Control Them
There are a lot of myths out there about controlling Japanese beetles. No research indicates that companion planting does any good. Special traps using floral lures and sex attractants are available, but Iowa State University does not recommend them because research indicates they do not work. These lures may catch beetles, but also attract even more beetles than they catch.
After reading various ISU and USDA materials, I'm listing below what I think is a good, reasonable, research-based way to control Japanese beetles in your yard.
Be forewarned, though, that these measures will only reduce the damage. Japanese beetles are here to stay and trying to keep them from doing any damage ever is as useless as trying to prevent, say, aphids from ever doing any damage.
• Avoid the plants they are most attracted to. (See a listing below.) In my case, they adore my hybrid tea roses, which are kind of a disease-ridden pain anyway, and not very cold-hardy. They're getting ripped out.
One The Iowa Gardener reader has a small crabapple she planted that is plagued by Japanese beetles and nearly dead. I recommended that instead of the time and expense of spraying, she just research a more resistant cultivar, remove the sick tree, and replant with the tougher tree.
So make some tough decisions and remove or avoid planting.
• Control the grubs. Talk to your lawn service, if you have one, about grub control products to apply.
If you do your own lawn weed and feed applications, consider GrubEx or other grub product. Apply in spring before grubs become active or are small. In Iowa, this is June or July.
The USDA recommends some organic measures as well. Nematodes are deemed effective. (Just be sure to get the liquid type you can spray). Bacillus thuringiensis (Bt) is also recommended.
Milky spore has limited effectiveness for Japanese beetle grubs unless your whole community uses it.
You can mail-order these through GardensAlive!,the best organic supply company I know of. Although I endorse them, organic measures such as these are somewhat less effective than chemicals and they can be prohibitively expensive for larger lawns.
• Pick off the adult beetles. Granted, some days I have barely enough time to brush my teeth, let alone get out there and pick insects off my plants. But especially for roses, raspberries, and other prized plants, it's helpful to get out there in the mornings with a bowl of soapy water and pick off the beetles and toss them to their deaths. (This is a great job for kids, by the way.)
• Spray plants you really care about. Do this when the adults are on the plants. I personally hate spraying chemicals. They kill beneficial insects as well as harmful, and I don't like exposing myself or my children to them.
So I doubt I will do this--especially with things like raspberries that I'm going to eat. Also, with Japanese beetles, you have to do multiple applications every several days.
Then there's the issue of Japanese beetles attacking very large plants, like certain types of crabapples, where spraying is impractical.
Still, if you're determined, ISU recommends carbaryl (Sevin), permethrin (Eight), or cyfluthrin (Tempo).
• Talk to your neighbors. Japanese beetles travel easily among yards. If your neighbors are also avoiding problem plants, controlling grubs, and spraying, it will reduce the problem overall in your neighborhood.
Iowa Plants Japanese Beetles
Are Most Attracted To:
Apple and most other fruit trees
Common mallow (Malva rotundifolia)
Roses, roses, roses!