During the hot summer months, we often observe an influx of shiny, slow-flying beetles in the south Denver metro area, particularly targeting vines, roses, shrubs, and some trees. These are Japanese Beetles, and their presence seems to be increasing annually. Not only do they feast on soft, fleshy leaves, but they exacerbate the problem by laying eggs in lawns. The resulting grubs then damage lawns by nibbling on the roots, leading to unsightly patches.

Natural Curative Options

There are various treatments available for lawn grubs, including both preventative and curative options. However, controlling the adult Japanese Beetles poses a challenge. Most curative products for these beetles can harm beneficial pollinators, such as bees. Therefore, the most effective strategy is to prevent the larvae from reaching adulthood.

The use of popular hanging traps can inadvertently draw more beetles to your lawn. These beetles often feed on nearby leaves and lay eggs in the surrounding lawn before entering the trap. If you do use a trap, it’s crucial to place it away from plants that Japanese Beetles typically feed on. Additionally, applying a treatment to control the grubs feeding on your lawn’s root system is recommended.

Natural Milky Spore Treatment

Managing Japanese beetle grubs in turfgrass often involves insecticides like trichlorfon (Dylox), halofenozide (Mach 2), and imidacloprid (Merit), which are effective in keeping grub numbers low. However, there’s a growing interest in alternative controls like beneficial nematodes and microbial-based insecticides. One such microbial insecticide is the milky spore disease, discovered in 1933 and commercially used since 1948.

Milky spore, known scientifically as Paenibacillus popillae, is a bacterium applied as a dust to turfgrass. It specifically targets Japanese beetle grubs, with no effect on other grub species. The grubs ingest the bacteria, which multiplies inside them, turning their internal fluids white and eventually causing death. The bacteria then spread in the soil.

Originally produced by infecting live grubs in laboratories, milky spore faced challenges in production and effectiveness. However, newer methods have improved its efficiency. Its success depends on environmental factors like temperature, moisture, and soil conditions. It works best in soil temperatures between 60° and 70°F (19° and 21°C), but may take longer to spread in cooler climates.

Milky spore spreads as grubs ingest it, with denser populations leading to quicker establishment. It binds to soil near the surface and can persist for up to 30 years if grub populations continue. While it effectively suppresses Japanese beetle populations, it may not show immediate results and doesn’t affect other grub species. Its use can be more costly than other methods, but it’s environmentally friendly, not harming beneficial soil organisms or wildlife. It’s also compatible with Tiphia wasps, a natural parasite of Japanese beetle grubs.

A natural solution to this issue is the use of Milky Spore, a bacteria that specifically targets the larvae of Japanese Beetles. This powdery substance, when applied correctly, can control the larvae in your lawn for 8-10 years. Milky Spore exclusively affects the white grub of the Japanese Beetle and is safe for people, pets, crops, and beneficial pollinators.

At Cowboy Lawn and Sprinkler, we now offer applications of Milky Spore to help manage the impact of Japanese Beetles and their grubs on your lawn. This treatment is an effective, environmentally friendly way to protect your lawn from these persistent pests.

If you want more information about lawn damaging grubs visit the CSU Extension and read about white grubs and other common lawn pests.