Guide to Identifying and Controlling Japanese Beetles Organically

Image: MSVG/Flickr

Japanese beetles are destructive garden pests that leave behind a wake of damaged and dying plants. They thrive in Maine and the rest of the northeast making their first appearances in July. There are 5 ways to keep these pests under control organically, bringing gardeners 1 step closer to a healthy and more productive garden.

How to Identify Japanese Beetles

Adult Japanese beetles grow to about ½ inch long. Their wing covers are bronze in color while the rest of their bodies are a metallic blue-green. The long legs of these beetles are easily visible, sticking out from their blocky bodies with their claw-like feet.

The larvae of Japanese beetles are called grubs. They are C-shaped and tannish-white in color. Larvae are fat and easy to see in freshly tilled soil.

When to Look for Japanese Beetles

Late June to early July is the prime time for Japanese beetles to make their first appearances. They feed on plants until late summer before burrowing under grass to lay their eggs. Once the eggs hatch into larvae, the larvae feed until cold weather moves in. Before the ground freezes, they burrow underground until spring when they emerge to feed on plant roots. Slowly, from May until June, larvae turn into adults continuing the life cycle.

Common Plants Japanese Beetles Attack

• Beans
• Peas
• Corn
• Tomatoes
• Trees
• Shrubs
• Fruits
• Vines
• Flowers

5 Ways to Control Japanese Beetles Organically

1. Floating Row Covers: Cover plants with floating row covers to protect them from Japanese beetles. During mid-summer if you notice beetles attacking uncovered plants, cover the smaller, more delicate ones with floating row covers to keep them protected.

2. Lawn Control: When July and early August roll around, let the lawn completely dry between waterings. This helps to control the egg population organically by drying them out.

3. Aerate the Lawn: During late spring and early fall, aerate the lawn to kill grubs.

4. Parasitic Nematodes: Apply these to the lawn in early spring or late fall. During this time, grubs are in the ground where the nematodes can feed on them.

5. Handpick the Garden Pests: Early morning is the best time to spot Japanese beetles on plants. Handpick them and drop them into a bucket or bottle of soapy water where they’ll drown.

Japanese beetles have the ability to chew through all the leaves on an entire plant making it important to control them from the day they emerge in the garden. Once they’re done feasting on one plant they’ll move on to another. Look for brittle, skeleton-like leaves or once healthy plants surrounded by dead foliage on the ground.

What’s Going on in Gibby’s Garden?

Japanese beetles have already begun to emerge in Gibby’s Garden. So far they’re more interested in the catnip than the vegetable plants. You can bet I’ll be out each morning with a bottle of soapy water handpicking these garden pests.

FYI: Did you know that Japanese beetles are attracted to some varieties of bamboo? I have some growing near one of my vegetable gardens. Though I don’t care for the plant because it spreads like crazy and is hard to get rid of, I leave a large patch undisturbed near my garden to lore the Japanese beetles out.

Check out Gibby’s Garden Diary to see what else is going on in the garden.

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Reference: Rodale Organic Gardening (2001). Basics:Pests Volume 7. Rodale Inc.