Is your garden hosting an all-you-can-eat buffet for Japanese beetle grubs? It’s time to turn the tables and send those unwelcome guests packing – and we’ve got just the tool for the job: milky spore. Here, you’ll find out how to use milky spore for grub control so you can say goodbye to those grubs and hello to a healthy, grub-free garden.
But before spending money on a milky spore product, you should know 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, confirm it’s Japanese beetle grubs you’re dealing with first.
How to use milky spore for grub control
A naturally occurring bacterium – milky spore (Paenibacillus popilliae) – has been used for Japanese beetle control since the 1940s. When Japanese beetle larvae (grubs) ingest the spores of this bacterium, they get a fatal disease known as milky disease or milky spore disease.
If Japanese beetle grubs are wreaking havoc on your once-luscious lawn, you must take action right away. Otherwise, they can leave a trail of destruction in their wake. So, get ready to outsmart those grubby gatecrashers with this biological control agent.
Tools and materials needed
To get started, you need to gather the following essentials first:
- Milky spore powder or granules (available online or wherever you buy garden supplies)
- Lawn and garden dispenser tube or drop spreader
- Sprinkler or hose spray nozzle
- Funnel
One of the benefits of organic pest control products is that they’re completely non-toxic to humans, pets, and beneficial insects. This natural treatment won’t harm anything other than Japanese beetle grubs.
However, the powder or granules can cause irritation if you get them in your eyes or mouth during application. So, wear safety goggles, gloves, and a face mask before you apply milky spore powder. Also, choose appropriate clothing like long sleeves, pants, and closed-toe shoes for added protection.
Step 1: Determine the optimal time
The goal is to apply the product when Japanese beetle grubs are actively feeding. For this reason, late summer and early fall are the ideal seasons for grub control. Here’s why:
- Grub activity peaks: During late summer and early fall, Japanese beetle grubs are actively feeding near the soil’s surface. Applying milky spore at this time ensures the grubs come into contact with the bacterium as they feed.
- Soil temperature: The bacteria become active and multiply when the soil temperature is between 60 and 70 degrees F.
- Life cycle disruption: Timing the application to coincide with grub activity disrupts their life cycle. Doing it when the grubs are near the surface prevents them from maturing into adult beetles, reducing the risk of future infestations.
Avoid windy conditions, as wind can carry the product away from the intended application area. To determine the exact timing for application, monitor your local weather and soil temperatures. You also can consult with a local agricultural extension office or garden center for guidance on the optimal timing for your specific region.
Step 2: Fill your spreading device with milky spore
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 tube (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.
If you’re using a lawn and garden dispenser tube, use a funnel to fill the dispenser. Slowly pour the powder through the funnel into the top end of the tube.
But if you’re using a drop spreader for granules, park the spreader on a flat, even surface, ensure it’s dry, and fill the hopper with the granules.
Note: Never use a broadcast spreader for applying spore powder. It’s so lightweight that the wind will carry it away if you try to broadcast it.
Step 3: Apply milky spore
Whether you’re using powder or granules, you want to cover your entire lawn, 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.
For milky spore granules: The package of the specific product you buy should include instructions on 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.
To ensure a successful application, remember to:
- Start at the perimeter
- Work in sections
- Maintain a steady pace
- Overlap passes
- Pay extra attention to infested areas
- Follow the recommended application rate
- Keep the spread even
- Cover the entire lawn
- Keep records of your treatment schedule
Step 4: Water milky spore into the ground
After you’ve covered your lawn with the powder or granules, you need to water it to help it 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 the treated areas lightly. The goal is to moisten the soil without creating runoff.
- Avoid overwatering your lawn, as excessive moisture can lead to other lawn problems. Follow the recommended watering practices for your grass type and region.
- Maintain consistent moisture in the treated areas for the weeks following application to help activate and encourage the bacteria to establish themselves in the soil.
Step 5: Repeat application
Milky spore is most effective when applied consistently over multiple years. Typically, you’ll want to apply the product annually for two to three years to establish a strong population of the beneficial bacteria in your soil. Create a schedule that works for your lawn care routine and stick to it.
Pro tip: After each application and watering, observe your lawn for changes in grub activity and the overall health of your grass. Over time, you should notice a decrease in grub damage and an improvement in your lawn’s condition.
How milky spore 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 disperse into the soil to infect more grubs.
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.
Benefits of using milky spore
- Environmentally friendly: This biological control agent is an eco-friendly alternative to chemical pesticides. It selectively targets the pest species without harming beneficial insects, wildlife, or the environment.
- Long-lasting: Once established in the soil, the milky spore bacteria can remain effective for 10 to 20 years or more, providing enduring Japanese beetle control.
- Safe for humans and pets: The treatment poses no threat to humans, pets, pollinators, or other animals. It’s safe for use in gardens, lawns, and areas where children and pets play. Homeowners can even apply it to edible gardens without worrying about contamination, and it won’t contaminate water through runoff, either.
- Preventative and curative: It controls existing grub populations and helps prevent future infestations by creating a hostile environment for the beetle grubs.
How to tell if your lawn has Japanese beetle grubs
So, how can you be sure you have Japanese beetle grubs? Look for these signs of grub damage:
- Brown patches: Look for brown, wilting patches of grass in your lawn. Grubs cause the affected grass to wither and turn brown. These patches are often irregularly shaped and can vary in size.
- Grass that lifts easily: Grubs feed on grassroots, weakening the connection between the grass and the soil. If you notice patches of grass that seem to detach easily when tugged, it’s a strong indicator of grub damage.
- Increased animal activity: Keep an eye out for increased animal activity in your yard, particularly birds, skunks, and raccoons. These animals are natural grub predators and will dig up holes in lawns infested with grubs.
- Seasonal patterns: Grub damage is often more noticeable in late summer and early fall when the grubs are close to the soil’s surface. Pay close attention to your lawn during these months, as this is when you’re most likely to spot signs of infestation.
- Soil sampling: If you’re unsure about the extent of the infestation or want a more precise assessment, consider taking soil samples. Use a shovel or a soil probe to collect samples from different areas of your lawn, especially where you suspect grub activity.
Once you’ve determined you have grubs, you must 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
If you detect adult Japanese beetles on the leaves of your plants in the summer, you can bet their larvae are living in your soil and chewing up the roots.
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 this bacterium would waste time and money.
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):
- Neem oil treatments
- Chemical pesticides
- Beneficial nematodes
- Lawn-aerating sandals
- Attracting natural enemies
If you want the best results, remember not to use milky spore in these conditions:
- Cold climate
- High grub density
- Limited lawn space
- Need for immediate results
- Soil quality and drainage issues
- New lawns or gardens with minimal grub activity
In some cases, a combination of approaches may be the most effective way to address grub infestations and maintain a healthy lawn.
FAQ about milky spore
How often do you apply milky spore?
You can apply the powder just once and still expect to see results.
However, St. Gabriel Organics (one of the largest producers) recommends six applications for faster, longer-lasting results. It recommends applying once in spring, summer, and fall for two years in a row.
How long does it take for milky spore to work?
Since it’s 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.
Will my ornamental plants get damaged by milky spore?
No, milky spore is not known to damage ornamental plants. It’s an environmentally friendly and highly targeted treatment that affects the grubs in the soil. Because it’s applied to the soil and not directly onto plants, it poses no risk to ornamental or garden plants, trees, shrubs, flowers, and vegetables.
However, always follow the manufacturer’s instructions and guidelines on the product label when applying the milky spore powder to ensure its safe and effective use in your garden or lawn.
Wipe out your grub problem
If you’ve already used milky spore, beetle traps, and other insecticides like diatomaceous earth, and they’re still not enough to control the beetle population in your garden, you can opt for integrated pest management instead.
Once 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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