3 Reasons Not to Use Milky Spore for Grub Control

Milky spores may sound like a funky ingredient in the kitchen but believe it or not it’s a type of bacteria, scientifically known as Paenibacillus (Bacillus) papillae.

I recently read a publication from the University of New Hamshire that stated there are more reasons NOT to use this product than to use it on your turf. The 3 reasons not to use milky spores for grub control are:

  1. Works only against Japanese beetles
  2. Insufficient Japanese beetle population
  3. Inconsistent soil temperatures

So, without further ado, let’s look at 3 reasons not to use milky spore for grub control in detail. 

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What is Milky Spore?

Long before the terms “integrated pest management” and “biological controls were coined, milky spore was a commercially available treatment to control and eliminate Japanese beetle larvae. 

Paenibacillus papillae bacterium is responsible for the milky spore disease, which is initiated when grubs feed on the roots of grasses in the soil and other plants and ingest the bacterial spores. 

After the larvae of Japanese beetles eat the bacteria, their body fluids become milky. This causes them to die and release more bacterial spores into the soil. 

milky spore

What Does Milky Spore Do?

Milky spore kills Japanese beetle grubs before they develop into adult beetles. Japanese beetles at their immature stage feed on the roots of lawns, turf, and other grassy areas.

Milky spore only kills larvae or Japanese beetles and remains in the soil for 2 to 10 years. Milky spore can be used in lawns as well as gardens without the fear of plant damage. 

When the Japanese beetle grubs eat the spores, the spores reproduce, and as they reproduce turn the grub’s internal fluids into a milky consistency, which then kills the insect within 7 – 21 days.

But the best part is that once the grub dies, the spores inside of it are released into the soil and infect more insects so you kill many birds with one arrow.

3 Reasons Not to Use Milky Spore

1. Works Only Against Japanese Beetles 

Apart from Japanese beetle grubs, there are many more types of grubs that damage turfgrass. including Asiatic beetles, June beetles, and May beetles. 

So a milky spore application would be a waste of cash and effort if you don’t have Japanese beetle larvae in your lawn. for which nematodes may be the only option for you. Here are some tips for using nematodes for grubs.

japanese bettles

2. Insufficient Japanese Beetle Population 

Whether Japanese beetle grubs or any other species of grubs, a small population is no reason for concern. However, a small population of Japanese grubs affects the efficacy of milky spores. 

A small population of Japanese beetle grubs will fail to increase the bacterial population enough to grow and spread into the soil. 

3. Soil Temperatures Must Be Between 60 Degrees to 70 Degrees for Three Months

Some states such as NH and VT do not receive consistently high soil temperatures. Adding to this, it can take a while for the bacteria to build up under ideal conditions, somewhere between 4 – 5 years, which isn’t ideal for tackling a large population of Japanese grubs. 

Other Grub Control Alternatives

There are many ways to go about controlling grubs in your lawn. I have written a few detailed guides on this topic, including what grub killer is best to use and when to apply grub control.

For a homemade remedy, you may look at using dawn dish soap for killing grubs in your lawn.

Grubs and MIlky Spore


Q: Which are better milky spores or nematodes?

A: Milky spores take a while to build up and work, whereas nematodes provide almost immediate control of grubs. 

Q: Is Milky Spore Safe?

A: Milky spore is an organic pest control product, therefore it is safe to use around people and pets.

Final Thoughts

Would I recommend using milky spore? Yes in the following situations! Milky spore is a great product for eliminating Japanese beetle grubs, but it is not effective against any other type of grubs.

You also need a sufficient Japanese grub population for milky spore to be effective and also have soil temperatures between 60 degrees and 70 degrees for 3 months consistently. 

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