They Are Here...
Japanese Beetles (Popillia japonica) are somewhat pretty, yet incredibly destructive, pests that first arrived in North America 1916 near Riverton, New Jersey. They have been driving gardeners nuts ever since. But it doesn’t have to be so! If you know the life cycle of Japanese Beetles, plus when & how to disrupt it, you can easily stop these nuisance creatures right in their hungry little tracks.
In Iowa, adult Japanese Beetles typically emerge from the soil mid-June through early July. They immediately begin chewing on & feeding on their go-to plants, which include varieties of rose, rose of sharon, linden, fruiting trees & shrubs, and so many more. They continue feeding feverishly on favorite plants for the next 4-6 weeks, putting out a congregation pheromone that acts as a “bat signal” to attract more beetles to the communal food source. This is typically the period of time gardeners are most aware of and frustrated by the wake of plant defoliation and destruction they leave behind.
But there are solutions!
Knocking beetles off the plants into a container of soapy water is an easy, no-cost way to eliminate beetles in the early days of infestation (or handpicking & squishing them). But if you get overrun by them, Bonide® Japanese Beetle Killer® is a ready-to-use spray available to kill Japanese Beetles by contact, as well as a number of other pests like aphids, stink bugs, flea beetles, whiteflies, and more. It contains the active ingredient Pyrethrum for a quick & easy kill. As always, our recommendation is to apply responsibly, per package directions, and late in the evening to minimize risk to pollinators.
Here’s the alarming part you can’t see happening at first: Every summer in Iowa, as the adult Japanese Beetles mate, they lay eggs in your lawn (oh, joy!). Within days, those eggs hatch into white grubs that burrow deeper into the soil. There, they will feed on grass roots all season long. Then they’ll hibernate over winter, and emerge as next summer’s adults. Evidence of their presence may be yellow, spongy spots in the lawn. The way to be sure? Peel back a 3-inch-deep, 1-square-foot flap of grass to check! If you find grubs, follow this next step.
What to Apply...
A single application of BONIDE Annual® Grub Beater® in spring or early summer can prevent grubs of all kinds from damaging your lawn all season long, especially killing the Japanese Beetle larvae (grubs) so they never get the chance to develop into adults. Applied anytime April through July, the product will help control Japanese Beetle infestation.
If you discover grubs in your lawn in late summer, roughly August through September, the protocol we recommend for Iowa is to apply BioAdvanced® 24 Hour Grub Killer Plus, which will immediately destroy all the grubs in your lawn, ensuring they don’t have the opportunity to hibernate over winter. If Japanese Beetle grubs have been a thorn in your side for multiple seasons, consider applying Milky Spore 3 times per year (spring, summer, and fall) for 2 years in a row. It’s a natural bacteria that actually invades the grubs, killing them and effectively inoculating your lawn.
Amazingly, certain plants are highly effective at repelling Japanese Beetles, and so they make for very purposeful companions to your beetle-susceptible plants! Consider planting fragrant perennials from the Mint family including Bee Balm (Monarda), Catmint (Nepeta), Lavender (Lavandula), and Meadow Sage (Salvia nemarosa). Varieties from the Onion family like Allium and Garlic are also effective.
Understanding how Japanese Beetles have managed to persist in Iowa means you know their destructive impact, life cycle, and that you have options for dealing with them. If you take the time to recognize the signs of their presence, you can also act to disrupt their plans by using physical barriers, control products, and by taking preventive measures for the future.