Japanese Beetles

Japanese beetles are the bane of many growers. These voracious pests feed on over 300 plant species, skeletonizing leaves and damaging flowers, fruits, and crops. Their ability to thrive in diverse environments makes them a persistent problem for growers across the United States.

These beetles are an invasive species that originally came to the US in 1916. Since then, Japanese beetles have spread south and west, covering most of the eastern United States and into the Midwest. Today, Japanese beetles continue to expand their range, causing significant damage to both home gardens and commercial agriculture.

Life cycle and biology

Japanese beetles are small beetles with a metallic green and copper color. They will often raise their hind legs in a defensive position to deter predators.

Females will lay their eggs in the soil in late summer, and the eggs will hatch into white, C-shaped grubs. These white grubs eat grass roots and can cause damage to lawns and turf. The grubs will overwinter and continue feeding when the weather warms up in the spring.

As the grubs grow and mature, they will pupate in the soil and emerge as adults. The adults then get to feeding and mating. The beetles skeletonize the leaves of plants, meaning they eat the leaf tissue between the veins.  

Preferred plants

Over 300 plants are on the menu for Japanese beetles. However, they do show a strong preference for certain plants. Some of their favorites include:

• Roses (Rosa spp.)
• Grapevines (Vitis spp.)
• Maple Trees (Acer spp.)
• Apple Trees (Malus spp.)
• Linden Trees (Tilia spp.)
• Corn, soybeans, and other row crops

They also attack ornamental flowers, fruit trees, and garden vegetables. While they feed on a wide variety of plants, they tend to avoid lilacs, boxwoods, and certain conifers.

Methods of control

Since Japanese beetles spend most of their time in the soil and their adult forms are highly mobile, it’s often best to target them in their grub stage.

While trapping has become a popular tactic, this can often bring more adults to the trap and they can spill over onto your vulnerable plants.

Some of the best methods for controlling them include:

Beneficial Nematodes – These microscopic worms target beetle grubs in the soil, killing them before they mature into adults. Check out our Hb NemaSeek nematodes and Sr NemAttack nematodes for grub control.

Milky Spore (Paenibacillus popilliae) – This naturally occurring bacterium infects and kills Japanese beetle grubs, but takes time to establish in the soil. It’s offered in both powder and granule forms.

Need Seed Meal – This neem tree derivative acts as both a soil amendment and a natural pesticide. When applied to lawns and garden beds, it disrupts the feeding and development of Japanese beetle grubs, reducing their survival rates. It also improves soil health, making it a dual-purpose solution.

Suppose you want to target adult beetles that are damaging your plants. In that case, you’ll want to adopt a more integrated pest management approach, combining both cultural and physical strategies with natural insecticide treatments.

Physical control - Removing beetles by hand in the early morning and dropping them into soapy water can help reduce populations in small gardens.

Row Covers – Using fine mesh netting can protect high-value plants during peak feeding periods.

Organic and Natural Insecticides – Using natural insecticides can help control Japanese beetle populations while minimizing harm to beneficial insects and the environment. Some of the best options include:

• Kaolin Clay – This fine clay powder forms a protective barrier on plant leaves, making them less attractive to Japanese beetles. It doesn’t kill the beetles but discourages feeding and egg-laying. Apply it early in the season before beetles become abundant.
• Pyrethrins – Derived from chrysanthemum flowers, pyrethrins are fast-acting contact insecticides that target adult beetles. They work by disrupting the nervous system, leading to paralysis and death. Pyrethrin sprays are best applied in the evening to minimize the impact on pollinators.
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  Azadirachtin(Neem Extract) – A key compound found in neem oil, azadirachtin disrupts the feeding and reproductive cycles of Japanese beetles. It acts as both a repellent and an insect growth regulator, preventing larvae from maturing into adults. Look for neem-based sprays with high azadirachtin content for the best results.
  

For effective control, apply these natural insecticides as soon as beetles first appear and reapply after rainfall. Combining these treatments with cultural controls and biological solutions offers the most effective long-term management strategy.

Japanese beetles are a persistent and destructive pest, but with the right management strategies, you can protect your plants. A combination of early intervention, natural predators, and selective treatments can keep their numbers in check. By targeting both the adult beetles and their soil-dwelling grubs, you can break their life cycle and minimize damage year after year.