Do Japanese Beetles Like Hydrangeas? How to Protect Your Flowers from This Destructive Pest

Hydrangeas are a beloved flower for many gardeners. Their large showy blooms come in a range of colors like pink blue, purple, white and even green. However, these gorgeous flowers aren’t immune to pests. One of the most destructive is the Japanese beetle. If you’ve noticed damage on your hydrangea blooms, leaves or stems, Japanese beetles may be to blame. Read on to learn why these pests target hydrangeas and how you can defend your plants.

Why Do Japanese Beetles Go After Hydrangeas?

Japanese beetles (Popillia japonica) are an invasive species originally from Japan. They were first discovered in the United States in 1916 and have spread to many states east of the Mississippi River. Adult beetles emerge from the soil in early summer and begin feeding on over 300 different plant species.

Hydrangeas happen to be one of their favorites. This is likely because of the large plentiful leaves and flowers that provide ample food. Japanese beetles are especially attracted to plants with lush juicy foliage, as well as ones with bright white flowers. Hydrangeas check both these boxes.

Once beetles locate suitable host plants, they release pheromones that attract more beetles to join the feast. It’s not uncommon for hydrangea flowers and leaves to become completely skeletonized when infestations are heavy.

Recognizing Japanese Beetle Damage on Hydrangeas

Japanese beetle feeding damage on hydrangeas is easy to recognize. You’ll see large, irregular holes chewed in the leaves, starting along the edges and veins. Flowers are also fed on, leaving ragged holes in the petals. Heavy skeletonization may occur, where all the soft tissue is eaten away, leaving only the veins behind.

Leaf damage starts out small, but progressively gets worse as more and more beetles arrive. They start feeding in the tops of plants, moving downward as food sources are depleted. Defoliation often occurs by mid-summer after the beetles have been active for several weeks.

Life Cycle of Japanese Beetles

To understand how to control Japanese beetles on hydrangeas it helps to know their lifecycle

• Spring – Overwintering grubs begin feeding on roots below ground. Grubs pupate into adult beetles.

• Early summer – Adult beetles begin emerging from soil. Beetles mate and females lay eggs in the soil.

• Mid-summer – Eggs hatch into grubs and begin feeding on roots. Adult beetles are actively feeding above ground.

• Late summer – Grubs continue developing, adult beetles die off.

• Fall & winter – Grubs burrow deeper into soil to overwinter.

The key to long-term control is interrupting this lifecycle at different stages using various control methods.

8 Ways to Protect Hydrangeas from Japanese Beetles

Here are the most effective tactics for protecting your hydrangeas from these hungry pests:

1. Hand Pick Adults

Hand picking beetles from plants is one of the quickest ways to reduce their damage. Check plants in the morning when beetles are more sluggish and easy to capture. Knock them into a container of soapy water to kill them. Be diligent, as more will continue emerging over several weeks.

2. Use Trap Plants

Some plants are extra attractive to Japanese beetles. Use these “trap plants” to lure beetles away from your hydrangeas. Good choices are larkspur, borage, marigolds, white roses and four o’clocks. Place them as far from your hydrangeas as possible.

3. Apply Neem Oil

Neem oil is extracted from the seeds of the neem tree. It coats plants with a bitterness that deters feeding. Apply it early in the season, before damage occurs, and reapply after rain. It also controls aphids, whiteflies and other pests.

4. Use Dead Beetles as Repellents

Believe it or not, dead Japanese beetles help keep live ones away. Crush some and place the bodies around your hydrangeas. The smell repels other beetles from landing. Combine with other methods for best results.

5. Apply Beneficial Nematodes

Nematodes are tiny worms that parasitize beetle grubs in the soil. Apply them in spring and fall. They won’t impact plants, earthworms or other beneficial insects. For best success, water soil before and after application.

6. Use Milky Spore Disease

Milky spore disease (Bacillus popilliae) is a naturally occurring bacteria that infects only Japanese beetle grubs. It comes in granular and powder formulations. Apply in spring or fall and reapply for a few years to build up the bacteria in your soil.

7. Encourage Natural Predators

Many birds, insects and small mammals feed on Japanese beetles. Attract them to your yard by avoiding pesticides and providing habitat like native plants, diverse foliage, and sources of food and water. Common predators include braconid wasps, ants, ground beetles and bacterium.

8. Use Row Covers

Floating row covers act as a physical barrier against adult beetles reaching your plants. Drape them over hydrangeas, securing the edges with stones, boards or landscape pins. For best results, apply in early summer before beetles are active. Ventilate on hot days.

Avoid Japanese Beetle Traps Around Hydrangeas

It may be tempting to hang Japanese beetle traps, but these can make problems worse. The traps contain lures that attract beetles into your yard. Once caught, the beetles release pheromones that call in even more. Place traps as far away from your garden as possible, or skip them altogether.

Be Persistent For Long-Term Control

Japanese beetles can be challenging to control because they have an extensive lifecycle and many generations per year. There is no single cure-all solution. The best approach is using multiple strategies consistently over several seasons to break their lifecycle. Expect to see incremental improvements over time rather than immediate results. Persistence and diligence are key for protecting your beloved hydrangeas.