Move over, spiders — Japanese beetles are quickly becoming one of the most feared pests in America (for avid gardeners, at least).
These pests will spend their whole life tormenting your landscape, from the time they’re grubs (aka white grubs) eating your lawn’s roots to when they become adult beetles and chew holes in all your trees and shrubs.
But you don’t have to resign yourself to that torment. You can prevent Japanese beetles if you think ahead and take some fairly simple precautions.
1. Control grubs
You can prevent adult Japanese beetles by exterminating the larvae, or grubs, before they ever have a chance to mature.
When to treat grubs: Grubs are active in the lawn in early spring and early fall.
Use these methods to get rid of grubs before they become Japanese beetles:
- Neem oil
- Lawn-aerating sandals
- Beneficial nematodes
- Milky spore
- Attracting birds
For more in-depth information about how to get rid of grubs, see How to Get Rid of Grubs in Your Lawn.
2. Stop watering your lawn
Japanese beetles will lay eggs in your soil, and those eggs need moisture to survive. The fewer eggs that survive, the fewer adult beetles you’ll have in your garden later.
So, you want your lawn to be as dry as possible during the beetles’ egg-laying season, which is usually June through August. During that time, stop watering your lawn and let it go dormant so the eggs die instead of hatching.
Disclaimer: A dormant lawn isn’t exactly pretty. Your grass will eventually start to yellow if you stop watering it, but if it’s healthy, it should spring back to life when you resume watering. One summer without a green lawn could be worth ending the cycle of grubs and Japanese beetles.
3. Install row covers
Keep your plants covered with row covers during the Japanese beetle’s feeding season, which varies depending on where you live but usually lasts from June through August. The covers will physically block beetles from reaching your plants.
WARNING: Row covers also keep pollinators off your plants. Don’t cover plants that need to be pollinated.
4. Plant Japanese beetle-resistant plants
You can plan your garden from the beginning to resist Japanese beetles. They’re less likely to infest your garden if you choose plants that they don’t like.
- Lilac bushes (Syringa spp.)
- Dogwood trees (Cornus spp.)
- Burning bush (Euonymus alatus)
- Magnolia trees (Magnolia spp.)
- Forsythia shrubs (Forsythia spp.)
Note: There’s no guarantee that Japanese beetles won’t attack these plants, but they’re less likely to attack these than other types of plants.
5. Use homemade Japanese beetle repellent sprays
One way to prevent Japanese beetles in your garden is to spray your plants with a smell that repels them. There’s no need for chemicals — you can make your own repellent at home.
Here are some recipes you can try:
- Garlic spray: Crush six or more cloves of garlic (depending on how concentrated you want the spray to be) and pour a gallon of boiling water over it. Leave the garlic to steep overnight. Strain out the garlic pieces, then put the water in a spray bottle.
- Cedar spray: Add a few ounces of cedar oil to 5 gallons of water. Pour some of the mixture into a spray bottle.
Whichever homemade spray you make, spray it liberally on your plants to repel Japanese beetles. You’ll have to re-spray every few days and after rain or heavy dew washes off the repellent.
How to get rid of Japanese beetles once you already have them
Even the most seemingly airtight prevention plan isn’t always enough to stop Mother Nature (you’ve heard of the Titanic, right?). You might end up with Japanese beetles in your garden despite your best efforts, but don’t worry — you can get rid of them.
These are some of the best methods for getting rid of Japanese beetles:
- Hand-pick them off your plants and drop them in a bucket of soapy water.
- Spray your plants with raw neem oil.
- Make your own pesticide spray with dish soap, vegetable oil, and rubbing alcohol.
- Leave out dead beetle bodies to repel the live ones.
- Collect live beetles using a drop cloth.
- Attract natural enemies to help control the Japanese beetle population.
- Plant geraniums, which paralyze Japanese beetles when ingested, in your garden.
- Plant a “bait” garden to keep Japanese beetles away from your prized plants.
- Set up Japanese beetle traps far away from your garden.
- Apply chemical insecticides to your plants.
We go into a lot more detail about all of these methods in our separate guide on How to Get Rid of Japanese Beetles.
How to tell if you have Japanese beetles
You’ll know if you have Japanese beetles because they leave very noticeable damage to your lawn and garden. Once you understand when Japanese beetles are active, you can keep an eye out for signs of damage and the bugs themselves.
About Japanese beetles
Japanese beetles (scientific name Popillia japonica) are an invasive species from Japan, but these days, they’ve made themselves at home all across the Midwestern and Eastern United States.
One of the most important factors of an effective Japanese beetle control plan is understanding when to look for them and their damage. If you apply the right treatments at the right stages of their life cycle, you can prevent and exterminate them.
First wave of grubs: The year’s first wave of Japanese beetle grubs (the larval stage) emerges from deep underground in spring when the ground thaws. These nearly full-grown grubs are hard to exterminate, and they’ll eat the roots of your lawn, turning your grass brown.
Adult Japanese beetles: The larvae grow into adult Japanese beetles and begin feeding on plants in late June in most places, although they can rear their heads as early as mid-May in the warmer South. Adults eat plants and lay eggs in the soil until August or September, by which time they’ll all die out.
Second wave of grubs: Remember those eggs that the adult Japanese beetles laid in summer? In early fall, those eggs hatch into grubs that start eating grass roots and turning the lawn brown again. This young grub stage is the most vulnerable stage in the life cycle to pest control methods.
Signs of Japanese beetle damage
If you have Japanese beetles in your garden, you probably have grubs in your lawn, too, and vice versa.
Adult Japanese beetle damage: Adult Japanese beetles eat around the veins of leaves, so what’s left is a “skeleton” of the leaf. Many gardeners say the leaves look like lace. Look for this type of damage from June to August.
Grub damage: Grubs eat grass roots, which means the grass can’t get water or nutrients, so it turns brown and dies. If you find brown patches in your lawn, tug on the grass. Does it come up from the soil easily? Grubs could be the cause. Look for this type of damage from April to May and August to September.
Physical appearance of Japanese beetles
In most cases, you can easily see the Japanese beetles themselves crawling around on your plants. Here’s what they look like:
- Size: About ½ inch long
- Shape: Scarab shape with hard, shell-like wing covers
- Color: Metallic green head with coppery wings and white hairs along the sides
Grubs live in the soil, so they aren’t as easy to see. You can test for grubs by digging up a 1-square-foot section of your lawn and inspecting the soil. Here’s what you’re looking for:
- Size: Up to 1 inch long
- Shape: Worm-like bodies, usually (but not always) curled into a C-shape
- Color: Milky white body with brown head
If your soil test reveals more than 10 grubs in the 1-square-foot area, you have an infestation on your hands.
FAQ about preventing Japanese beetles
No. In fact, Japanese beetle traps are attractants, and they only catch about 75% of the bugs they attract. Traps are more likely to cause an infestation than prevent one.
The best scent to repel Japanese beetles is the “death stench” of dead beetles. If possible, collect some dead Japanese beetle bodies in small containers and place them around your garden.
If dead beetles aren’t an option (we get it — yuck!), here are some other scents that repel Japanese beetles:
Vinegar sprays can kill Japanese beetles, but they also kill your plants. We don’t recommend using vinegar directly on your plants, and you would have to spray it directly on the leaves for effective Japanese beetle control.
Even horticultural vinegar isn’t safe to use on your plants. Horticultural vinegar has a higher acetic acid content than household vinegar, which means it’s even better at drying out plants and killing them. This product is intended to kill weeds, not to use on plants for pest control.
Japanese beetles eat more than 300 plant species across several plant families. Some of their favorite plants are rose bushes, grapevines, hibiscus, and raspberry.
Make the first move on Japanese beetles in your garden
You’d be surprised how quickly a group of Japanese beetles can chew through all the leaves and flowers in your garden. That’s why the best course of action is protecting your garden before they ever set their greedy little eyes on it.
If your area is prone to Japanese beetle attacks, you’ll want to take preventive measures like the ones we described above every year beginning in spring. Stay one step ahead of these buggers, and you’ll save yourself a whole summer of pain!
Need help preventing or getting rid of Japanese beetles? Reach out to a pest control expert in your area.
Main Photo Credit: Richard Malo | Pixabay