The Flower Bin

 Milky Spore and the Japanese Beetle

To reduce Japanese beetle pressure organically, start by targeting the grubs in your lawn and garden soil.  Controlling the larval stage helps interrupt the beetle life cycle before adults emerge and cause damage. 

Japanese beetle eggs are laid in small clusters in moist, well-irrigated soil, typically from late summer into September. Each female can lay 40 to 60 eggs during this time. The eggs are small, white, and oval-shaped, buried about 2 inches below the soil surface. They generally hatch within 10–14 days, and the grubs will feed until colder weather drives them deeper into the ground. 

Milky Spore is a naturally occurring bacterium (Paenibacillus popilliae) used as a biological control to kill Japanese beetle grubs in lawns and gardens. It is highly specific, meaning it only targets Japanese beetle larvae and does not harm humans, pets, beneficial insects, or other wildlife.  

The key to Milky Spore effectiveness is to identify the grub you find in your lawn or garden.  Japanese beetle grubs feature a brown head, 6 legs and V-shaped rear end spines. Other white grubs have orange or grayish heads, 6 legs, and a round/bloated rear end.

If you’re unsure, bring us a sample of the grubs present in your lawn and we’ll identify them.

Japanese beetle grubs ingest the spores while feeding on grass roots. Once ingested, the bacteria multiply rapidly inside the grub, causing the grub’s hemolymph (insect blood) from clear to milky white that kills within 7 to 21 days. 

As the infected grub decomposes, it releases billions of new spores back into the soil, naturally spreading the treatment. In areas with large Japanese beetle grubs, the spore can become self-sustaining.

Milky Spore treatment focuses primarily on lawns because turfgrass serves as the main breeding ground for Japanese beetles. The dense root systems found in grass provide an ideal food source for grubs, making turf grass the area where the beetle population is typically greatest. As a result, treating your lawn directly addresses most Japanese beetle grubs living locally.

It should be noted that while Japanese Beetle grubs are primarily turf pests, they may also be found in other moist, root-rich areas, including, garden beds with ornamental grasses or turf-like plants, compost-rich, well-watered soils where plant roots are available, areas around ornamental trees and shrubs with shallow or accessible roots

In these non-turf settings, grubs may damage ornamental plants, garden crops, or non-turf grasses. Their feeding pattern is similar wherever they occur: they chew on fine roots, creating patchy and irregular damage. The key is the availability of roots. If there are fine roots available for grubs to feed on, chances are there are grubs nearby. 

Along with Milky Spore, it is important to strengthen lawn vigor with proper watering, mowing, fertilization and aeration; a healthy turf tolerates moderate grub feeding.

If you’re dealing with a variety of white grubs in your lawn, including Japanese Beetle grubs, you might consider using a broader spectrum insecticide, such as Hi-Yield Grub Free Zone.