Milky spore disease (Bacillus popillae) was developed in the late 1930s as a biological control for Japanese beetles. It is used to suppress the population of Japanese beetles in turf and around plants. Milky spore disease is considered the best long-term control of Japanese beetles.
Japanese Beetle Larvae
The translucent oval eggs of Japanese beetles are white to cream-colored. The larvae are white with yellow heads and two rows of spines that form a "V" on the last abdominal segment. They are about an inch long and usually found curled in a "C" shape. Japanese beetle larvae eat the roots and underground stems of plants. They are considered a serious pest of turf grasses.
Adult Japanese Beetles
Japanese beetles are about 2 inches long with shiny metallic green bodies and coppery-bronze wing covers. There are 12 white spots along the sides and rear of the beetles, and small tufts of white hair on the tips of their abdomens and the sides of their wing covers.
The beetles feed on more than 275 species of plants, including ornamental plants, fruits and vegetables. They chew the tissue between the veins of the leaves and chew on ripening fruit.
How Milky Spore Disease Works
When the powder or granules of milky spore disease are spread on the affected areas of lawn or planting areas, the Japanese beetle grubs eat the roots with the spores attached. The spores begin to reproduce, eventually killing the grubs. When the grubs die, millions of new spores are released into the soil.
Milky spore disease develops best when the temperature is between 60 and 90 degrees. In areas where the temperature remains above 70 degrees for several months, effective control can be achieved in as little as 1 year. It may take 3 to 4 years to achieve effective control in colder climates.
Once milky spore disease is established, the spores remain dormant in the soil for years and chemical treatments for Japanese beetles are not needed. Milky spore disease does not affect caterpillars, earthworms or warm-blooded animals.
Milky spore disease is sensitive to cold temperatures and does not work well on cool wet heavy soils. It does not control other types of grubs.