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  • Writer's pictureAndy Hemmer

Diatomaceous Earth for Japanese Beetles

Updated: Jul 9


japanese beetle

Japanese beetles (Popillia japonica) are a notorious pest for gardeners and farmers alike. Originating from Japan, these beetles have become widespread across North America, causing significant damage to a variety of plants, including roses, grapes, and various fruit trees. One of the natural and environmentally friendly methods to combat these pests is using diatomaceous earth (DE). This blog post will explore the life cycle and habits of Japanese beetles, what diatomaceous earth is, how it works against these pests, and how to use it effectively.



Japanese Beetles: Life Cycle & Habits


Life Cycle

Understanding the life cycle of Japanese beetles is crucial for effective control. Their life cycle consists of four stages: egg, larva (grub), pupa, and adult.


  • Egg Stage: Female beetles lay eggs in the soil during midsummer, usually around grassy areas. Each female can lay 40-60 eggs, which hatch in about two weeks.

  • Larva Stage: The eggs hatch into white grubs that live in the soil, feeding on roots and organic matter. This stage lasts from late summer through spring. The grubs grow through three instars (developmental stages), becoming increasingly destructive to lawns and pastures.

  • Pupa Stage: In late spring, the grubs pupate in the soil. This transformation period lasts for about two weeks, during which the grubs develop into adult beetles.

  • Adult Stage: Adult beetles emerge from the soil in early summer, feeding on the foliage and flowers of over 300 plant species. This feeding period typically lasts for 4-6 weeks, during which they also mate and lay eggs, starting the cycle anew.


Habits

Japanese beetles have several habits that make them particularly troublesome:


  • Feeding: Adult beetles are voracious feeders and prefer warm, sunny days. They skeletonize leaves, leaving only the veins, which can lead to significant defoliation and weakened plants.

  • Swarming: These beetles tend to feed in groups, making infestations appear suddenly and causing rapid damage.

  • Flight: Japanese beetles are strong fliers, capable of traveling several miles to find food and mates, which helps them spread quickly.

  • Grub Feeding: The larvae feed on the roots of grasses and other plants, causing patches of dead or dying grass. This damage is often noticed in late summer and early fall.


Understanding these habits and the life cycle of Japanese beetles helps in planning effective control measures, including the use of diatomaceous earth.



What is Diatomaceous Earth?


diatomaceous earth

Diatomaceous earth is a naturally occurring, soft sedimentary rock that is crumbled into a fine white powder. It is composed of the fossilized remains of diatoms, a type of hard-shelled algae. DE has a high silica content, making it abrasive yet safe for humans and animals when used correctly. It is commonly used in various applications, including as a natural pesticide.



How Does Diatomaceous Earth Work?


Diatomaceous earth works primarily through a mechanical process rather than a chemical one. The microscopic sharp edges of the DE particles cut through the exoskeleton of insects like Japanese beetles. This abrasion causes the insects to dehydrate and die, as their protective exoskeleton is compromised, and they lose essential moisture.



Benefits of Using Diatomaceous Earth


  • Non-Toxic: Unlike chemical pesticides, DE is safe for humans, pets, and the environment. It does not contain harmful chemicals that can linger in the soil or water.

  • Broad Spectrum: DE is effective against a variety of pests, including ants, fleas, bed bugs, and of course, Japanese beetles.

  • Long-Lasting: When kept dry, diatomaceous earth remains effective for a long period. It does not lose its potency unless it becomes wet and then dries out again.

  • Organic Gardening: DE is permitted in organic farming, making it an excellent choice for those who prefer organic methods of pest control.



How To Use Diatomaceous Earth For Japanese Beetles


To effectively use diatomaceous earth against Japanese beetles, follow these steps:


  • Identification: First, identify the presence of Japanese beetles. These beetles are about 1/2 inch long with metallic green bodies and copper-colored wings.

  • Application Timing: Apply DE early in the morning or late in the evening when beetles are less active. Avoid applying during wet or windy conditions as moisture reduces DE's effectiveness, and wind can cause it to blow away.

  • Protective Gear: Wear a mask and gloves when applying DE to avoid inhaling the fine powder.

  • Application: Dust the DE directly onto plants where you see beetle activity. Focus on the undersides of leaves where beetles tend to congregate. You can also sprinkle DE around the base of the plants.

  • Reapplication: Reapply after rain or heavy dew, as moisture can cause DE to clump and lose its effectiveness.

  • Monitoring: Regularly check the plants for beetle activity and reapply as necessary. Consistent application is key to controlling the beetle population.



Additional Tips


  • Companion Planting: Planting garlic, chives, or tansy near susceptible plants can help repel Japanese beetles naturally.

  • Trap Crops: Consider planting a trap crop like geraniums. Japanese beetles are highly attracted to geraniums, and the flowers can incapacitate them, making them easier to collect and dispose of.

  • Handpicking: Combine DE application with handpicking beetles off plants and dropping them into a bucket of soapy water. The hand pick method is a tried and true method to help control them.

  • Alternative Methods: You can use other means and pesticides to kill japanese beetles including japanese beetle traps, milky spore powder, and even neem oil. None of which are safer than DE.



Diatomaceous earth is a valuable tool in the fight against Japanese beetles. Its non-toxic nature and mechanical method of pest control make it a preferred choice for organic gardeners and environmentally conscious individuals. By understanding how to use DE effectively and incorporating additional pest management strategies, you can protect your plants from these destructive beetles and enjoy a healthier garden. Using diatomaceous earth requires diligence and consistent application, but its benefits far outweigh the effort, providing a safe and effective way to manage Japanese beetle infestations.





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