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What Is Milky Spore?

By Elizabeth Balarini ; Updated September 21, 2017
White grubs are the larvae of Japanese beetles.
beetle image by Anton Chernenko from Fotolia.com

The Japanese beetle is a shiny black beetle that attacks rose bushes and fruit trees. The beetles travel in large groups, and lay their eggs in lawns. Their eggs lay dormant for an entire year, and go undetected until they hatch. The hatchling grub worms feed on the roots of grass, causing patches of lawn to turn yellow and die. There are pesticides that eradicate grub worms, but these pesticides are harmful to the environment, pets, and humans. Milky spore is a environmentally safe "bio-pesticide" that kills Japanese beetle eggs and grub worms.


Milky spore is also referred to as "milky spore disease." Milky spore disease is a bacteria that is host-specific. This means that the bacteria only effects one thing. The only host that the bacteria targets is the larvae of the Japanese beetle (popillia japonica), which are referred to as grub worms. The bacteria is naturally occurring, and is sold in powder form for the treatment of grub worm infestation. Milky spore is so named because of the effect it has on grubs: As the spores multiply within the grub's body, slowly killing it, its tail end changes from black to milky white.

How it Works

Milky spore disease acts as a shield on the lawn. Hungry grub worms eat their regular diet of grass, but ingest milky spore disease along with it. The bacteria makes the grub worms sick, and they die in approximately one to three weeks. According to Michelle Niedermeier, who is the community integrated pest management coordinator affiliated with Penn State and Pennsylvania Department of Agriculture, the bacteria spores continue to multiply inside the dead grub; when the body decomposes, up to 2 billion new milky spores are released, further treating the lawn. Niedermeier adds that it may take a season or two before this death and release of new spores have a significant impact on the lawn.


The Chicago Tribune advises that homeowners treat their lawns for grubs only when the grub infestation is "large enough." In lawns that have at least 10 to 12 grubs per square foot, with damaged sod that pulls back from the soil easily, the use of milky spore disease is justified. Otherwise, the grub population is too small to incubate and spread a significant number of spores throughout the lawn.

Application of the granules is best done when the soil temperature is between 60 and 70 degrees.


Catherine R. Weeden and Anthony M. Shelton of Cornell University's College of Agriculture and Life Sciences say that the main appeal of using milky spore disease is its safety for humans and other animals. Nor does the bacteria have any negative effect on plant life.

Although it is non-toxic and will not cause illness, it is always wise to use a particulate-safe mask when working with powders, especially if you have asthma or another lung-related illness.


Reapplication of milky spore disease is rarely needed. According to The Chicago Tribune's website, a single application of milky spore disease powder has been known to effectively protect lawns from grub worms for 20 years or more. Because decomposing grubs enable the bacteria to multiply and spread, the inoculation is actually more effective two to four years after the treatment is applied.


About the Author


Elizabeth Balarini is a freelance writer and professional blogger who began writing professionally in 2006. Her work has been published on several websites. Her articles focus on where her passions lie: writing, web development, blogging, home and garden, and health and wellness. Balarini majored in English at the University of Texas at San Antonio.