How Does Milky Spore Work?

Milky spore products work by introducing a specialized strain of bacteria into the soil in your yard. This bacteria causes the deadly milky spore disease in Japanese beetle grubs. However, the bacteria in milky spore is completely harmless to all other organisms. So, milky spore is an organic, safe solution that kills invasive grubs. Because the milky spore bacteria breeds in infected grubs, as long as there are some grubs in the soil, the bacteria will continue to reproduce. This can create a self-sustaining population of grub-killing bacteria that survives for up to 20 years.

How does milky spore work?

What is Milky Spore?

Milky spore is the common name for grub control products that contain Paenibacillus popilliae bacteria. When you follow our steps to apply milky spore, you are spreading dormant bacteria that will be activated when it is watered into the soil.

  • Milky spore is made of P. popilliae bacteria.
  • The bacteria in milky spore is deadly to Japanese beetle grubs.
  • Milky spore is harmless to every organism other than Japanese beetle grubs.
  • You can use milky spore in an organic lawn or garden.

Adding bacteria to your soil may seem strange, but this strain of bacteria is only harmful to one organism—the Japanese beetle grub. Since the Japanese beetle grub feeds on grass roots and is not native to North America, it is an invasive lawn pest. Essentially, milky spore products contain a bacteria that kills one species of grub. It is safe to use on all lawns and completely organic.

How Does Milky Spore Kill Grubs?

When a Japanese beetle grub ingests soil that contains P. popilliae bacteria, it becomes infected with milky spore disease. This is where milky spore gets its name. This disease destroys the grub’s internal organs and turns their fluids milky white. A grub infected with milky spore will die within 7 to 21 days. The bacteria that reproduces in the infected grub then enters the soil and will infect the next grub.

How Effective is Milky Spore?

Milky spore is highly effective at killing Japanese beetle grubs. However, this is the only species of grub it kills. There are several species of grubs that kill grass and damage lawns, including chafer beetle grubs and June bug grubs. So, milky spore will only be effective if the harmful grubs you’re fighting are the grubs of Japanese beetles. If you want to use an organic method to kill all grubs, check out our article comparing the benefits of milky spore vs. beneficial nematodes.

How Long Does Milky Spore Last in Soil?

Milky spore can remain active in the soil for up to 20 years after application. More commonly, milky spore remains active for 5 to 10 years after you spread it. The reason milky spore is so long-lasting is that the milky spore bacteria reproduces as it kills grubs. As long as a few Japanese beetle grubs try to invade your lawn each year, the milky spore will kill them and reproduce. This creates a long-lasting barrier against grub invasion.

What are the Advantages of Milky Spore?

The main advantage of milky spore compared to grub pesticides is that milky spore is extremely environmentally safe. Since milky spore only targets invasive Japanese beetle grubs, it won’t kill any native wildlife, won’t damage soil microbes, and won’t harm earthworms. Using pesticides to kill grubs in your lawn can be dangerous to wildlife, pets, and humans. Milky spore is completely harmless to humans, pets, and other beneficial creatures. So, it has big advantages over competitor products.

  • Safe for wildlife, pets, and humans.
  • Will not harm soil organisms, unlike grub pesticides.
  • Low cost.
  • Easy to use.

In addition to being very safe to use, milky spore is inexpensive and very easy to spread. Our comparison of milky spore powder vs. granules found that the powder is the best budget option. Plus, the only tool you need to spread milky spore powder is this inexpensive lawn applicator.

What are the Disadvantages of Milky Spore?

The biggest disadvantage of milky spore is that it only kills one species of grub. Any grubs that are not Japanese beetle larvae won’t be harmed by milky spore at all. So, it’s best to use milky spore when you are sure you are dealing with Japanese beetles.

  • It only kills one species of harmful grub—Japanese beetle grubs.
  • Other grub species will not be harmed by milky spore.
  • Your milky spore application may be super effective or almost useless, depending on the grubs infesting your lawn.

To make matters more complicated, it’s very hard for non-experts to tell the difference between one species of white grub and another. Japanese beetle grubs look similar to other harmful grubs. The main difference is the pattern of hairs on the end of their body. Since it’s almost impossible to be sure if you’re dealing with Japanese beetles or a different type of grub, using milky spore is a bit of a risk. It might work extremely well, or it might be totally useless against the grubs in your lawn.

What is Milky Spore?

Before you use milky spore on your lawn, review these facts:

  • Milky spore is a bacteria that kills Japanese beetle grubs.
  • The bacteria in milky spore infects the grubs with a deadly disease.
  • Grubs die 7–21 days after coming in contact with milky spore.
  • Products containing milky spore are considered organic.
  • Milky spore is harmless to all organisms that are not Japanese beetle grubs.
  • Harmful grubs that are not Japanese beetle grubs will not be killed by milky spore.
  • You can apply milky spore easily and at a low cost.
  • After application, milky spore continues working for 10–20 years.

Although milky spore does not kill all grub species, it is worthy of use as a first-choice grub solution. If the grubs in your lawn happen to be Japanese beetle grubs, you can wipe them out within months and prevent grubs from invading your lawn again for years to come.

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