Up until about the year 1919, Japanese Beetles were not an issue. Now, due to virtually zero natural predators, you have probably noticed these shiny green herbivores munching on most of the vegetation in your yard or garden.

Adult Japanese beetles feed on over 300 different varieties of plants. In fact, there’s not much that they won’t snack on. They can skeletonize your plants in a matter of days causing them to be quite the headache to most gardeners.

Why are these beetles such a problem?

With over 300 varieties of plants, shrubs, trees and non woody plants for these guys to feast on – there really is no yard that is safe if Japanese Beetles are around.

Individual bugs alone are no threat to your garden, but once the mature beetles release their congregation hormone you will notice more and more of these metallic green eating machines flocking to your yard. When there is an infestation in your garden you will notice as they show up in droves.

Japanese Beetles typically run in cycles with the females eating for a few days then moving underground to lay eggs then re-emerging to feast on your foliage again. Female Japanese Beetles lay about 50 eggs in their life cycle. The larvae of the beetles feast on the tender roots of turf grass, this is why you might notice brown patches in your yard.

In late summer/early fall you can dig up a 1 square foot of turf and count how many grubs are in your yard. If the number exceeds 12 in that one patch, you might want to consider applying grub control to your yard (we will touch on that later in this blog).

Getting to know the stages of development

There are 4 different stages of development that Japanese Beetles go through in their life cycle and there are different control methods for each stage. The stages are:

Eggs – Japanese Beetle eggs are small, oval, white eggs that are laid in the soil. If the moisture is good then the eggs will absorb it and enlarge and become rounder as they develop.

Larvae – This is the stage that is potentially so damaging to lawns. These white grubs move to the tender roots of your turf grass to graze and mature. You can identify Japanese Beetle Larvae by their v – shaped series of bristles on their raster (the underside of their abdomen).

Pupae – This stage is where the grub begins turning into a beetle. The pupae will mature into a cream color and age into a red/brown.

Adult Beetle – These hard bodied bugs are metallic green in color with brown wing covers. They are less than ½ inch in length and will emerge from the ground between May & early July. Their lifespan is 30-50 days and this is when they feed on your landscape and reproduce.

As soon as these guys emerge from the ground, they look for suitable vegetation to begin eating. Eventually they will begin reproducing and continue repeating the cycle until the end of their season.

As the soil heats up (80 – 90 degrees F is prime conditions) the larvae will move closer to the surface, eating turf grass as they grow.

As the soil in the fall cools, the grubs burrow deeper into the soil where they will wait to reemerge come springtime so, in order to really take control of the issue (if you find you have a large infestation) there are methods you can take to ensure your plants, trees and shrubs are safe come the following season.

Controlling Japanese Beetles

Timing is key when it comes to Japanese Beetles. Understanding their lifecycle will only help in your battle against these armored flying pests. From about May – July, while the beetles are actively feasting on your foliage, hand picking or applying insecticide will be your most effective way to eradicate them.

Minimizing the larvae is typically done in late summer to early fall as the grubs are feeding on the roots of turf grass. The grass will take up the grub killer and in turn will kill the larvae as they eat the roots.

If you think you are going to totally eradicate the issue, don’t set yourself up for disappointment. It is impossible to get rid of Japanese Beetles as more will flock into the area as the current crop is killed. There are not many natural controls for these guys as of yet even though efforts have been taken to help control the population. You will have to use more than one hands on method to help control them.

Removing by hand

The first method for mature adult Japanese Beetles is removing them by hand. Typically I bring a bucket, half full of water with some dawn dish soap, out to the plants that are being decimated and I pick the beetles off by hand and toss them into the water. Does this seem cruel? Yes. Is it effective? Also yes.

Insecticidal Soap & Pheromone Traps

Insecticidal soap will kill mature Japanese beetles but only if the soap is sprayed directly on the beetle who is feasting on your plants. Insecticidal soap does not have any residual effect, this means that any of the spray left on the foliage will not kill the remaining beetles, but it will harm other insects such as beneficial ladybugs.

Pheromone traps are an effective way to lure beetles away from plants that you are trying to protect. Simply hang the trap near the property line away from the plants you are wishing to protect. You will have to keep an eye on the receptacle and empty it (into a bucket with some water).

Pesticides for these Pests

Any synthetic insecticide will eradicate Japanese beetles, but will also pollute the surrounding areas and also harm beneficial insects.

A more conscious option would be neem oil or a spray containing pyethrin. Pythrin is a biodegradable substance that is from chrysanthemums. This type of insecticide should be applied selectively and directly on the Beatles themselves. Pyethrin has no residual effect on surrounding areas.

Grubicides for long term care

Attacking Japanese Beetles at the source is the most effective long term care for this particular variety of pest. You can pick up a granular grubicide from us here at Devitt’s and it is often applied in the late summer to early fall while the grubs are close to the surface of the soil in your lawn.

Milky spores & Nematodes

Milky spores – a natural bacteria that will attack grubs in your yard. Once the grubs are infected they will die in 7-21 days and the organisms will multiply in the soil as the dead grubs decompose. Milky spore can protect your yard for up to 20 years once established, but will take a few years to really become established.

Nematodes – are natural little worms that take up home in soil. There are nematodes that will specifically target japanese beetle grubs. Nematodes will die in direct sun, so apply them on a cloudy day or at dusk when the sun is going down.

With japanese beatles you may notice a few new inhabitants in your yard as well. Moles and Skunks love to snack on the grubs so eliminating japanese beetles will also send other unwanted guests looking for a new yard to call home.

As always, you can stop into Devitt’s to learn more about how you can start eliminating these Beatles. We have what you need to start making a dent in the issue as well as long term applications to begin protecting your yard for years to come.

We would be more than happy to answer any question that you might have.
Happy gardening!