How to Use Milky Spore for Grub Control

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Japanese beetle grub

Milky implies a sweet treat, and spore implies some kind of alien invasion, but milky spore has nothing to do with either. Milky spore is a bacteria that infects and kills some white grubs that cause lawn damage. Want to know how to use milky spore for grub control? Just follow these 5 steps. 

But before you spend money on a milky spore product, you should know that it’s only effective for Japanese beetles. If the white grubs in your lawn are a different species, milky spore won’t do anything to them. So, make sure it’s Japanese beetle grubs you’re dealing with first. 

How to apply milky spore to your lawn in 5 steps

What you’ll need

  • Milky spore powder or granules (available online or wherever you buy garden supplies)
  • Lawn and garden dispenser or drop spreader 
  • Funnel
  • Safety goggles
  • Face mask
  • Gloves
  • Sprinkler or hose spray nozzle 

Step 1: Apply in early fall

Grubs have to eat milky spore for it to infect them, so the best time to apply milky spore is in early fall when grubs feed most actively. You can apply milky spore in spring and summer, as well, because grubs are present pretty much any time the ground isn’t frozen.

The ideal soil temperature for milky spore is between 60 and 70 degrees. This is another reason why fall, when temperatures are cooler, is the ideal time for milky spore applications.  

Step 2: Cover yourself

One of the benefits of organic pest control products like milky spore is that they’re completely non-toxic to humans, pets, and beneficial insects. Milky spore won’t harm any living thing other than Japanese beetle grubs. 

However, milky spore powder or granules can cause irritation if you get them in your eyes or mouth during application. So, it’s a good idea to put on safety goggles and a face mask before you apply milky spore. Wear gloves, too, so you don’t get the substance on your hands and then transfer it to your face. 

Step 3: Fill your spreading device with milky spore product 

Since you have to apply milky spore all over your lawn, the easiest way to do it is to use a lawn and garden dispenser (a long, tube-shaped device with holes in the bottom that you can build yourself or find online for around $10) or a drop spreader. Never use a broadcast spreader for milky spore. It’s so lightweight that the wind will carry it away if you try to broadcast it. 

If using a lawn and garden dispenser for milky spore powder: Use a funnel to fill the dispenser. Slowly pour your milky spore powder through the funnel into the top end of the tube. 

If using a drop spreader for milky spore granules: Park the spreader on a flat, even surface, make sure it’s dry, and fill the hopper with milky spore granules. 

Step 4: Cover the whole lawn with milky spore

Whether you’re using powder or granules, you want to cover your entire lawn with milky spore, not just the area showing signs of grub damage. If you fail to cover the whole lawn, the grubs can simply migrate from the treated area to an untreated area.

For milky spore powder: Release about 1 teaspoon of milky spore powder every 4 feet in a grid pattern, covering your entire lawn. You can spoon out each teaspoon by hand or use a lawn and garden dispenser to save yourself the stooping. With a dispenser, simply tap it on the ground every 4 feet to release an appropriate amount of powder. 

Here’s a video showing how to use a dispenser to apply milky spore powder:

For milky spore granules: The package of the specific product you buy should include instructions telling you which setting to use on your drop spreader. Set the spreader to the correct setting, then roll it across your lawn slowly to ensure even coverage.

Step 5: Water milky spore into the ground

After you’ve covered your lawn with the milky spore product, you need to water the whole lawn to help the milky spore soak into the soil, where it will reach the grubs. 

Set your sprinkler system or a spray nozzle on your garden hose to the gentlest spray setting possible, then water the lawn for about 15 minutes. Water every area where you applied the milky spore product. 

As soon as you’ve watered the product into the soil, you’re free to walk on the grass and mow the lawn as usual. 

What is milky spore?

Milky spore (Paenibacillus popilliae) is a bacterium that has been used for Japanese beetle control since the 1940s. When Japanese beetle larvae (aka grubs) ingest the spores of this bacterium, they get a fatal disease known as milky disease or milky spore disease. 

Here’s how it works: The grub eats the spores, which reproduce inside of it. As they reproduce, they turn the insect’s internal fluids to a milky consistency. This kills the grub in seven to 21 days. When the grub dies, the spores inside of it disperse into the soil to infect more grubs. And so the cycle continues for 10 or even 20 years, as long as there are grubs for the spores to infect. 

Milky spore will never completely eradicate all grubs in your soil. But it will reduce the grub population below the damage threshold (10 to 12 grubs per square foot), thus preventing further damage to your lawn. 

How to tell if your lawn has Japanese beetle grubs

Remember, milky spore will only help your lawn if the problem is Japanese beetle grubs. If you’re dealing with any other pest or lawn disease, applying milky spore would be a waste of time and money. 

So, how can you be sure you have Japanese beetle grubs? Look for these signs of grub damage:

  • Brown patches of grass
  • When you tug on the grass, it pulls out of the soil easily 
  • Your grass feels spongy 
  • Holes in your lawn from birds, skunks, or other predators of grubs digging them up

Once you’ve determined you have grubs, you have to figure out if the pests are Japanese beetle larvae. While it’s incredibly difficult to tell the difference between different species of grubs, it’s easier to identify adult beetles. 

Identifying features of adult Japanese beetles:

  • Copper-colored wings
  • Shiny, metallic green head
  • Round tufts of white hairs along the side of the body 
  • Damage on plants: holes in the leaves, leaving nothing but the veins or “skeleton” of the leaf behind

You’ll find adult Japanese beetles on the leaves of your plants in summer. If you have adult Japanese beetles on your property, you can bet their larvae are living in your soil and chewing up your grass roots.

FAQ about milky spore

1. How often do you apply milky spore?

You can apply milky spore just once and still expect to see results. 

However, St. Gabriel Organics (one of the largest milky spore producers) recommends six applications for faster, longer-lasting results. It recommends applying once in spring, summer, and fall for two years in a row. 

2. How long does it take for milky spore to work?

Milky spore is not an immediate solution to grub infestation. You may not see a significant decline in the grub population for three years in warm climates or even longer in cold climates. 

3. How long does milky spore last?

Milky spore bacteria remain active in your soil for up to 10 years. Sometimes, the bacteria last 15 to 20 years, as long as there’s a continuous supply of grubs to recycle and spread them. So, even though milky spore takes a long time to get started, the tradeoff is long-lasting results. 

Milky spores spread through the grubs themselves, so how long they last depends on the grub population. If there are no more grubs in your soil, the milky spores will disappear, too. 

4. Is milky spore harmful to humans?

edible gardens without worrying about contamination, and it won’t contaminate water through runoff, either. 

5. Can you put milky spore on wet grass?

Yes, you can apply milky spore on wet grass. But the grass doesn’t have to be wet before application. 

When not to use milky spore 

What if the grubs in your lawn are the larvae of other species of beetles, not Japanese beetles? Or what if you want to see results fast? Milky spore isn’t right for you in these cases. But that doesn’t mean you have to let the grubs win. 

These other grub control methods effectively kill all species of grubs, and they work faster than milky spore (although they won’t last as long without repeat treatments):

  • Chemical pesticides
  • Beneficial nematodes
  • Neem oil treatments
  • Lawn-aerating sandals 
  • Attracting natural enemies

Learn more about these methods in our guide on How to Get Rid of Grubs in Your Lawn

Now that you’ve wiped out your grub problem, Lawn Love’s local lawn care pros can help your lawn look its best again — and stay that way.  

Main Photo Credit: Japanese beetle grub by ElHeineken | Wikimedia Commons | CC BY 3.0

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