6 Natural Ways to Keep Japanese Beetles Out of Your Garden

Japanese beetles (Popillia japonica) are invasive pests with metallic-green bodies and copper-colored wings. While they may appear visually interesting, they can cause significant damage to lawns and gardens, targeting over 400 plants, including roses, grapes, raspberries, and more. Adult beetles skeletonize foliage, while their larvae, known as grubs, feed on grass roots, resulting in brown patches and dying lawns.

Managing Japanese beetles can be challenging since they often emerge in large numbers during the summer. Adult beetles typically come out of the ground in late June and early July and continue feeding on flowers, leaves, and crops into August. The good news is that now is the perfect time to take proactive measures and establish a mitigation plan.

Using these methods recommended by our experts, you can significantly reduce Japanese beetle populations and the damage they cause to your garden and lawn.

Use Beneficial Nematodes

Using beneficial nematodes is a safe, organic way to control many garden pests, such as Japanese beetles, without resorting to synthetic pesticides, says Casey Williams, mentor and consultant at Soil Food Web School. Nematodes are microscopic, thread-like roundworms that naturally inhabit the soil and serve as an effective organic pest control. The small worms attack pests in their larval or pupal stages, disrupting their feeding and reproductive cycles, says Williams.

Apply the worms to your garden by mixing them with water and spraying the mixture on the soil or by applying them directly to the trunks and branches of trees. Nematodes are sensitive to strong sunlight, so use them on overcast days or in the evening. The best time to use nematodes is when the Japanese beetles are in the grub stage and most active in the soil. Aim to apply the nematodes in June.

Apply Neem Extract Spray

Neem extract, derived from the neem tree, contains azadirachtin, a natural insecticide effective against Japanese beetles. Eric Nieusma, co-owner of Maine Hill Farm, recommends using organic neem extract or concentrate products to eliminate Japanese beetles.

Mix 1 tablespoon of the extract or concentrate with warm water in a spray bottle. Start spraying at the bottom of the plant's stalk, focusing on the undersides of the leaves where pests often hide. Use a fine-mist spray setting to minimize runoff, and limit applications to once every seven days to prevent blocking of photosynthesis. Spray at sunset to avoid leaf burn, and shake the sprayer occasionally. Neem oil is safe for honeybees and other beneficial insects.

Make a DIY Garlic and Peppermint Spray

A garlic and peppermint mixture can deter Japanese beetles, says Barry Messinger of Messinger’s Hardscape Landscaping and Design, LLC. The strong, distinct scents of specific essential oils can prevent pests from entering the garden. Peppermint oil, in particular, contains menthol, which disrupts the biological processes of beetles, making them less likely to linger in areas where the scent is present.

Combine 2 cups of water, 1 teaspoon of liquid soap, 10 drops of peppermint oil, and 10 drops of garlic extract in a spray bottle and shake well. Spray the mixture in the early evening when the sun isn't shining directly on the leaves. Apply the spray at least once a week and avoid spraying before rainfall. Messinger recommends testing the spray on one leaf before applying it more widely to prevent plant burn. If the test leaf shows no adverse reactions, such as drooping, you can proceed with the whole application. The solution won't kill the beetles but will deter them from bothering your plants.

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Hand-Pick Adult Beetles

Hand-picking the beetles is an effective way to manage infestations. The best time to hand-pick these pests is in the early morning when they tend to be sluggish, says Ankit Singh, assistant professor of sustainable agriculture at the University of Maine. "This simple method is surprisingly effective for small infestations and reduces the number of beetles laying eggs in your soil."

Start by placing a drop cloth under the affected plants and gently but firmly shaking the plants. The beetles will fall onto the fabric. Afterward, collect the beetles and place them in a bucket of soapy water. Walk around your plants and inspect the leaves to ensure you collected all the beetles. Although this process can be time-consuming, it is worth the effort.

Use a Trap Crop

Trap crops are an effective way to manage Japanese beetles by attracting them away from desired plants. Recommended options include marigolds, which lure beetles and deter other pests; borage, known for its beautiful blue flowers that enhance soil quality; white geraniums, whose fragrance appeals to beetles; grapevines, which are particularly attractive to these pests; evening primroses, which bloom at night and attract beetles with their sweet scent; and zinnias, colorful flowers that attract beetles and beneficial insects.

To maximize effectiveness, plant trap crops at the edge of your garden. Regularly monitor the plants for beetles and use methods such as hand-picking or insecticidal soap to control them. This approach helps to protect your main crops while keeping pest populations in check.

Use Row Covers

To protect your garden from Japanese beetles, consider using row covers during their peak activity, which runs from late June to early August. These pesky insects can wreak havoc on your plants, so a little preparation goes a long way. When setting up row covers, ensure you secure the edges with staples or bury them in the soil. This keeps the beetles out while allowing fresh air and sunlight to nourish your plants. Ensure the fabric is loose enough to accommodate plant growth.