How to control Japanese beetles organically

Last Updated on May 5, 2022 by Aaron von Frank

Trying to figure out how to control Japanese beetles organically? Here’s how we do it… And if you have ducks or chickens, these methods can also provide you with some free poultry food. 

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We love producing our own homegrown organic produce and free-range duck eggs. Our family spends a lot of time out in our half acre edible organic landscape as does our flock of Welsh Harlequin ducks. 

That means we’re extra careful about what we use to control pests, preferring to utilize biological controls and integrated pest management rather than pesticides.  

Japanese beetles: a challenging pest insect for organic control methods

Perhaps the worst summer pest insect we experience is Japanese beetles. 

In case you’re wondering, yes, domesticated ducks and chickens LOVE Japanese beetles. However, they’re not adept at catching the beetles on their own, so human assistance is required. (More on that below.)   

Even if you have beetle-eating ducks or chickens roaming about, they won’t be able to control Japanese beetle populations. 

3 things you should know about Japanese beetles

Here are three things you should know about Japanese beetles which helps put our recommended control regimen into context: 

1. Japanese beetles have few native predators. 

Japanese beetles are a non-native invasive insect that has only been in the US for about a century. This means they have very few natural predators here – and the predators that do eat them don’t do so in enough quantity to control their populations. 

For instance, we often see Florida predatory stinkbugs, praying mantises, and wheel bugs eating Japanese beetles. 

Some species of wild birds, anoles, and other predators also eat Japanese beetles. However, Japanese beetles are so prolific that predators make virtually no impact on their overall populations. 

2. ADULT Japanese beetles are only out for a short time window in the summer, but their populations are enormous. 

Mature/adult Japanese beetles are only around for about 30-45 days before they reproduce and die. The adult stage occurs during a 6-8 week window in the summer that has a bell curve, e.g. there’s a beginning, a peak, then a decline in population numbers before they fully disappear.

In some areas of the country, there can also be a smaller “second wave” of Japanese beetles. 

In our Zone 7b garden, we usually start seeing Japanese beetles towards the end of June and they finish up in early August. During the peak of their breeding season, swarms of Japanese beetles are present on their favored plants.  

In our edible landscape, favorite Japanese beetle plants are:

• blackberries and raspberries,
• persimmons,
• grapes,
• cherries,
• peaches,
• elderberries,
• edible roses,
• paw-paws,
• pomegranates,
• aronias,
• Arctic kiwi, and
• chestnuts. 

As you can see from this list, Japanese beetles have a wide and varied diet, which is one of the things that makes them so difficult to control. If they had a preference for only one species of plant, controlling them would be easier and more targeted. 

3. The majority of a Japanese beetle’s life is spent underground as a root-eating larva. 

The vast majority of a Japanese beetle’s life is actually spent underground in larval form. The adult females burrow into the ground to lay eggs multiple times while they’re alive. Each egg hatches within a couple weeks and the larvae emerge and start munching on plant roots. (In urban settings, this often means grass roots.) 

While it might be frustrating to think about all those horrid Japanese beetle grubs just waiting for their chance to mature and start eating your plants’ leaves, this larval period is actually a choice time to start implementing control methods, as we’ll detail below! 

How to control Japanese beetles organically in your yard or garden

First, let us state the obvious: every yard, garden, or small farm is different and unique. The exact methods you use to control Japanese beetles may vary depending on your budget, the size of your space, what types of plants you’re growing, and even how willing your neighbors are to cooperate! 

Second, you should know that there is no SINGLE way to control Japanese beetles. These pests defy silver bullets.

Instead, you should think about combining methods in an integrated fashion in order to provide the best Japanese beetle control possible while accepting that 100% eradication isn’t possible – unless you’re willing to make your landscape a toxic wasteland to all other life as well. 

The organic control methods that we detail below are intended to help you reduce the population of adult Japanese beetles to the point that they’re no longer able to cause significant damage to your plants. 

Step 1: Kill as many Japanese beetles in larval form as possible.

There are two great biological controls that you can use to kill the larvae of Japanese beetles: 

1. Milky spore

Milky Spore is the bacterium Bacillus Popilliae. While harmless to humans, pets, and other wildlife, it wreaks havoc on Japanese beetle larvae.

How does Milky Spore work?

When spores of Milky Spore are eaten by underground Japanese beetle larvae, the grubs die which then releases billions of new spores into the soil around them. The spores remain in the soil killing Japanese beetle larvae for up to 20 years. 

How do you use Milky Spore?

Follow the instructions on the product you purchase. Generally, you want to apply it to the soil with a spreader anytime from spring to fall. Ideally, you can apply it before a rain or irrigate immediately after applying to make sure it soaks into the soil. 

A really good Milky Spore product is St. Gabriel’s granular Milky Spore. A single $40 bag provides up to 7,000 feet of coverage. 

2. Certain species of predatory nematodes

Predatory nematodes are microscopic predators. Different species of predatory nematodes eat different prey species.

Perhaps the best predatory nematode species for controlling Japanese beetles is Heterorhabditis bacteriophora.

How do predatory nematodes work?

Predatory nematodes will seek out and consume Japanese beetle larvae in your soil. 

How do you use predatory nematodes?

You add the nematodes into a water dilution then apply them as a soil drench any time from spring through fall when soil temperatures are 45°F (7°F) or higher. Dry soil and winter temperatures kill predatory nematodes so they don’t last as long as Milky Spore when it comes to controlling Japanese beetles. 

A good predatory nematode product is BioLogic’s Steinernema Feltiae (Sf) Beneficial Nematodes. Added benefit: they also kill flea larvae! (Product note: At ~$40, this is only enough nematodes for 200 square feet.)

Budget recommendation:

If you have to choose between one or the other, we’d definitely recommend Milky Spore as your first line of defense against Japanese beetles. It’s more immediately affordable on a square foot basis and a single application can continue to kill Japanese beetle larvae for up to two decades. 

Are there limitations to this Japanese beetle control approach?

The only downside to using Milky Spore and predatory nematodes to control Japanese beetles are that they only work on the land where they’re applied. Japanese beetle larvae can still mature on nearby land and the adults can fly on to your property. 

This is where it makes sense to talk to your neighbors about joining the fight! That said, if you have a severe Japanese beetle infestation, chances are that your land is full of plants they eat and the females are laying lots of eggs there.  

Step 2: Trap ADULT Japanese beetles. 

Do Japanese beetle traps work?

We’ve heard people say that Japanese beetle traps don’t work — or even worse, they actually attract more Japanese beetles to your property. However, the research is actually mixed on the subject.

Some research has shown that when used properly, Japanese Beetle traps can actually be quite effective. We’d advise you to read more about that research and to also read the actual research papers referenced (if you want to get more geeky).

There are a quite a few quality Japanese beetle traps available. The traps last for years; you just need to add new bait each summer. 

Japanese beetle traps are the primary method we use for controlling ADULT Japanese beetles.

Our favorite part of using traps? We get to feed our ducks fresh Japanese beetles daily during the beetles’ breeding window, which our ducks LOVE. All that extra nutrition makes our ducks healthier and their eggs healthier too. 

If you don’t have poultry, just compost your dead Japanese beetles. 

Now let’s jump into HOW to use Japanese beetle traps: 

a. Carefully place your Japanese beetle traps.  

First, put your traps 30 feet away from any valuable plants (example: fruit trees) OR put the traps in the middle of your duck/chicken area.

If you live in a sparsely populated area, you could even set the traps up far away from your garden or orchard areas, then “harvest” the insects daily for your hungry fowl.

b. Pay attention to the Japanese beetle trap height. 

Set the Japanese beetle traps up so that they’re no more than 2-3′ off the ground. The research studies that found Japanese beetle traps to be ineffective actually put the traps much higher up out of the beetles’ natural flight path.

c. “Harvest” the Japanese beetles daily.  

Once per day, dump the trapped beetles into a bowl of water and let your ducks, chickens, turkeys or other fowl enjoy a protein and vitamin-rich feast. *Warning: If you don’t dump the beetles into water, they’ll fly away.

Don’t have poultry? Dump the beetles into a bowl of soapy water instead, and they’ll quickly drown.

Be sure to empty your Japanese beetle traps daily, since the smell of dead beetles may dissuade living beetles from coming to the trap.

If you’re setting up your Japanese beetle trap in your chicken/duck run, another option (pictured above) is to set your trap up with the bottom open right over the top of a large bowl of water. This way the beetles fall through the trap and into a bowl of water, where your flock eats them. You don’t have to empty or clean the trap.

This method provides your fowl with a steady stream of insect snacks throughout the day, rather than one single gorging at night. The downside with this option is that a strong wind/storm could reposition your trap, allowing the beetles to escape. So you may want to tie it in place or to the ground so it doesn’t move around.

Step 3: Only if necessary, utilize organic pesticides. 

If you’re utilized the first two steps (killing Japanese beetle larvae and trapping adult beetles) and you’re still dealing with an infestation of Japanese beetles, you may be forced to use an insecticide as a last resort. 

In this case, we’d encourage you to utilize an OMRI-listed organic pesticide rather than a synthetic pesticide. Both will kill non-target species, but organic pesticides don’t tend to be as environmentally persistent or have as many negative externalities. 

For small gardens with only a few plants, a single bottle of Bonide’s Japanese beetle killer may suffice. For larger gardens or small farms, products like Debug (predominantly neem oil) will do.  

Also, be mindful of application rates and times. Apply only at dilution ratios indicated on the product label and apply as late in the evening as possible to minimize pollinator exposure.

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FAQs about Japanese beetles for poultry owners

How many Japanese beetles can you feed to your ducks or chickens? Can you overdo it? Are Japanese beetles healthy for them? 

Let’s dive into those questions! 

Nutritional composition of insects:

What’s the nutritional composition of insects? It varies somewhat by species, but according to this FAO report:

“Rumpold and Schlüter (2013) compiled nutrient compositions for 236 edible insects, as published in the literature (based on dry matter). Although significant variation was found in the data, many edible insects provide satisfactory amounts of energy and protein, meet amino acid requirements for humans, are high in monounsaturated and/or polyunsaturated fatty acids, and are rich in micronutrients such as copper, iron, magnesium, manganese, phosphorous, selenium and zinc, as well as riboflavin, pantothenic acid, biotin and, in some cases, folic acid.”

Note that this analysis is based on “dry matter” and that the nutritional quality of living insects is likely much higher than dried insects. It’s also important to remember that insects are relatively high in phosphorus and low in calcium, two critically linked minerals that are essential to have in balance for healthy, egg-laying ducks and chickens to maintain hard egg shells.

You CAN overfeed insects to your birds, causing a calcium deficiency which could lead to soft eggs, poor bone and feather health, and other symptoms related to calcium deficiency. Just as with people, a balanced diet is important, so just be mindful of this possibility with your flock’s food.

Our ducks gorge on Japanese beetles every June and have not had any resulting soft egg shell or other health issues. If you have far more Japanese beetles than your poultry can or should eat, you might also consider freezing them in bags and rationing them out throughout the rest of the year, similar to mealworms or soldier fly larvae.   

Insects are a nutritional powerhouse that will aid in your poultry’s health, especially when they need slightly higher protein diets during the laying season. So, why not take your problem (Japanese beetles) and turn it into a solution (edible eggs)?

Mind you, we still don’t look forward to Japanese beetle season, but we don’t meet it with the dread we once did. As for our ducks? They refer to Japanese beetle season as “second Christmas.” Free gifts and treats really can fall from the sky!

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We hope these tips help you control your Japanese beetle problem organically!