Regional Gardening Reports :: National Gardening Association

In the Garden:
New England
July, 2004
Regional Report

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Early morning is the best time to catch Japanese beetles by surprise and knock them into a can of soapy water.

Foiling Japanese Beetles

While late spring and early summer tend to be a mad frenzy of garden prep and planting, midsummer is a time of slower-paced rituals -- watering, weeding, checking for ripe peas and beans, pinching off basil blossoms -- and patrolling daily for Japanese beetles. No insects get under my skin more than Japanese beetles (although rose chafers are vying for that honor this year). They can turn a shrub that's full of lovely rose blossoms in the morning into a devoured mess by evening. If you don't have a morning ritual of strolling through your garden, you can miss the flowers entirely.

There is hope, however, because there are some non-toxic control measures that work reasonably well if you take a little time to know your enemy. So let's get better acquainted.

A Beetle Primer
In my area I usually see the first beetles in late June or early July. These adults spent the winter underground as white grub larvae, after which they spent two weeks in early spring as pupae before emerging from the ground as full-fledged beetles. Because they spend so much time -- 10 months of the year -- as larvae, that stage is a good one to target for control. But more on that in a minute.

Both males and females feed on plants -- eating and mating, mating and eating. Periodically the females take a break and burrow about 3 inches into the ground (usually in grass) to lay eggs. This cycle is repeated until the female lays 40 to 60 eggs. The eggs hatch by midsummer, and the young grubs begin to feed on grass roots. If you dig in the soil you can often see the inch-long, curled grubs. In late autumn, the grubs burrow deeper into the soil (4 to 8 inches), where they remain until early spring.

Beetle grubs are a favorite food of skunks, and if you have an infestation of Japanese beetles you may see holes in your lawn where skunks have dug for their dinner. While you don't want to encourage skunks as control agents, you can make use of some other organisms that also kill grubs: milky spore disease and beneficial nematodes.

Milky Spore
Milky spore is a bacterium, Bacillus popillae, sold as a powder that you spread on the soil to kill grubs. The grubs ingest the spores, which grow inside their host, giving them a milky appearance. Grubs eventually die from the disease. The disease slowly builds up in the soil as the grubs ingest the spores, then die and release spores back into the soil. Milky spore causes no harm to beneficial soil creatures or humans. It tends to work better in warmer regions and when used community wide.

Beneficial Nematodes
Beneficial nematodes are microscopic, parasitic worms that prey on grubs. They carry bacteria that infect the grubs, and the combination of nematodes and bacteria kills the grubs. Nematodes are typically sold on a sponge that you immerse in water, then you spray the solution on the soil. I've had an increasingly severe Japanese beetle problem, and last year when I peeled back a layer of sod to check for the larvae, I was appalled at the numbers of grubs. So I sprayed nematodes on the lawn, and this summer the number of pesky beetles is much lower than in past years.

Be the Early Bird
Adult Japanese beetles love nothing more than to spend the sunny daytime hours romping on your plants. But they are not morning creatures. They awaken sluggish and become active as the sun becomes stronger. Then they lose steam as the evening temperatures drop. So you have to employ a little one-upmanship and use that cycle to your advantage. Visit your garden in the cool, early morning or late evening hours with a can of soapy water, and knock the beetles into it. They won't fly away like they will during midday if they sense movement nearby. They may perform their "drop dead" routine and fall to the ground. But if you position your can underneath the leaves, you will catch most of them.

Neem Insecticide
The oil of the neem tree, which is used as an active ingredient in several different botanical insecticides, kills adult Japanese beetles. It's safe for use on food plants, but check the label of any product carefully in case other not-so-safe ingredients are added to the formulation.

The Allure of a Lure
Commercially available Japanese beetle traps contain both mating and food lures, and they can work quite well. The problem is, if you place them in your garden you'll attract more beetles to your yard than you had before. And the traps only capture about 75 percent of the beetles they attract. Place the traps at the edge of your yard, far away from plants you're trying to protect.

When it comes to a pest as nasty as Japanese beetles, it's best not to rely on just one type of control. I'm going to spray nematodes again and keep up with the morning ritual of dunking the beetles into a nice, soapy bath. I also remove any ripe or diseased fruit from my plants because the scent can attract beetles. So take your morning cup of coffee into the garden and start making the rounds. Just be sure you pick up the right container to take a sip.

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