The Beetle Invasion: Protecting Your Garden From Japanese Beetles
by Katerie Prior

When I first moved into my home, my backyard was a gardener’s perfect blank canvas. The house was less than eight years old; it had almost no landscaping, and the previous owner did very little with the yard except mow it. As a former apartment owner and patio container gardener, I couldn't wait to start planting.

It was early June in the northern Midwest, so I still had time to plant a garden. I already had a mental list of things I wanted to plant: roses, cherry trees, grapes, zinnias, marigolds, and Lombardy poplars. But it wasn't going to be all planning. Several curlicues of dead grass marred the yard. Still, that didn’t bother me. It just needs some fertilizer and a little watering, I thought.

As the summer progressed, however I began to worry. Everything on my mental list was planted, but I noticed holes in the petals of my roses, zinnias, and marigolds. The leaves of my cherry tree and grapes also had huge gaps and were doing poorly despite all my efforts. At the top of the poplars and cherry trees, the leaves were eerily skeletonized, eaten so only the veins remained. The culprit was a metallic green, peanut sized bug with light-brown wings - the Japanese beetle.

Japanese beetles are the most widespread turf-grass pests in the United States. Native to Japan, these bugs were first discovered in the U.S. in 1916 at Riverton, N.J. With no natural predators on this continent, these beetles have been slowly spreading across the country over the past few decades.

Adult Japanese beetles eat over 400 plant varieties, (including everything on my list that I planted). They lay eggs up to four times a year in moist turf, like freshly watered grass, and around plants, particularly trees. The eggs hatch in August and the grubs feed off plant roots, causing the C-shaped patches of dead grass in my lawn.

The calling cards of the Japanese beetle are skeletonized plants and usually, you will find multiple bugs on plants being devoured. If you don’t see the bugs, but have the C-shaped patches in your yard, you can pull the grass back and see the grubs, which grow from ½"-1" long, eating roots. Even if you don’t see beetles or dead grass, but you have a sickly plant in your yard, you can dig carefully around the roots of an afflicted plant to look for grubs.

As an environmentally conscious gardener, my first response was to hand-collect and destroy the beetles. Although it sounds ineffective, the collecting slowed the damage. The presence of even one beetle can attract others since Japanese beetles can fly anywhere from 1-5 miles to look for food, mates, and a suitable place to lay eggs. This is why pheromone traps, which are sold at gardening shops as another means of getting rid of Japanese beetles, are more humorous than effective and can actually attract more beetles to your garden.

Pesticides, particularly those that specifically target grubs, can prevent the beetles from destroying your plants. The availability of particular pesticides effective against Japanese beetles depends on the state you live in, so its best to consult a local garden shop on which ones to use.

Pesticides, however, only protect your garden for the season. In recent years, an organic control method, Milky Spore disease, has become more popular with gardeners for fighting Japanese beetles. When applied to the ground, this powdery bacterium is ingested by the grubs where it multiplies until it kills the grubs. On their demise, more Milky Spore bacteria are redistributed in the soil for other grubs to eat.

Because Milky Spore continually regenerates as it destroys Japanese beetle grubs, it can last for 3-10 years. It is also safe to use around children and pets while being non-toxic to the environment. You can buy the powder in canisters in most specialty gardening shops. Although the bacteria can be a bit pricey, Milky Spore is a worthwhile investment.

As with most situations in a garden, the best defense is to plan for the next season. If you realize you have the beetles, you can apply a pesticide to your plants and yard to keep the bugs from eating and laying eggs. In late July - early August, spread Milky Spore on the yard following the directions on the canister. Milky Spore can even be used in conjunction with pesticides and fertilizers. If you have C-shaped patches, you may even want to pull up the turf and sprinkle the bacteria directly on and around the grubs. You can also reapply Milky Spore in the spring to destroy grubs that may have withstood the winter.