How Do You Get Rid of Japanese Beetles on Knockout Roses?

Measuring only ½” of an inch in length, Japanese beetles are little creatures that love to munch on over 300 species of plants, and one of their favorite treats? Knockout Roses.

You may have noticed the leaves of your knockout roses and other plants look as though the leaves have turned to something resembling lace.

Japanese beetle eating rose leafPin

This is a telltale sign that it’s time to combat Japanese beetles (Popillia japonica) in your garden causing real damage to plants and vegetables.

What Is the Japanese Beetle?

Japanese beetles are very recognizable. It’s hard to miss their metallic green head, with coloring that continues onto their thorax. The wings are a metallic copper color.

If all of that wasn’t enough to distinguish this beetle from the rest, the abdomen’s sides have stripes with white hairs in a series of 5.



The larva of Japanese Beetles are not as unique as the adult beetles and look similar to any other white grub.

Two beetles on rose bush.Pin

The most recognizable thing about the larva that lets us know there are Japanese beetles nearby is the pattern of spines and hairs that line the abdomen’s tip. 

The new adults usually begin to emerge from the ground in late June and July.

Japanese Beetles have ravaged crops and plants since their introduction into the US in 1916.

While this bug has successfully made its way to most of the 50 states, their infestation is predominantly in States just east of the Mississippi River.

Beetles on a flower.Pin
Photo Credit: Instagram @tonkadale

What Damage Do Japanese Beetles Cause to Knockout Roses?

These little bugs don’t merely eat leaves. Even their eating patterns are recognizable. These nasty pests consume the plant tissue around the veins, giving an appearance of lace to your plant’s leaves.

Knockout rose blossoms are often the most significant casualty of a Japanese beetle, given the overall plant.

Beetles on a rose; pest activity.Pin
Photo Credit: Instagram @richard.kosheluk

While a rose bush can usually survive a Japanese beetle’s onslaught, it cannot always come back or bloom from losing the blossoms.

Plants that have been a feeding ground for these insects appear skeletonized.

The result is that plants cannot restore health to the affected leaves, so they turn brown and die.

Beetles on a flower bud.Pin
Photo Credit: Instagram @thindseylalheimer_

Related: What Causes Knockout Roses To Get Holes In Their Leaves?

Different species of plants that commonly suffer from these pests include raspberries, birches, grapes, lindens, cherries, apples, and crabapples.

How to Control & Rid Your Knockout Roses of Japanese Beetles?

It is essential with Japanese beetles to get them the minute you notice they are there. It is astonishing how quickly their numbers can multiply, and the presence of just one or two beetles can attract hoards of them in no time.

Beetle on rose leaf.Pin
Photo Credit: Instagram @urbanfarmsista

Milky Spore

This method is best for the long-term relief of Japanese Beetles damage. It’s a fantastic decision to dust your lawn once a year over three years to eradicate these bugs.

Milky Spore is a disease developed in the 1930s. We find that Japanese Beetles are particularly susceptible to it as it disrupts their life cycle.

Beetles will contract the disease and spread it, causing entire populations of the beetle to kill off at one time. It is an effective method for control and easy to get your hands on Milky Spore. It is sold at most home improvement stores.

Green beetle on a red rose petal.Pin
Photo Credit: Instagram @cityfreshgardens_1

Insecticides

Insecticides can always be useful for killing unwanted insects. The chemicals will kill Japanese Beetles by shutting down their nervous system, resulting in their death.

While insecticides are an excellent option for a quick fix, they are not always the safest option for you and your family.

Additionally, some chemicals are often not approved in some areas.

Insecticides are most effective when used at dawn, just before the beetles emerge and become active.

Beetles on a wilted rose held in hand.Pin
Photo Credit: Instagram @billyvanbakker

Related: Tips On Getting Rid of Japanese Beetles Naturally

Neem Oil

Neem Oil is one of the safest methods of getting rid of Japanese beetles. It is non-toxic and sourced from the Azadirachta indica tree. It is essential to use this oil when the larvae are just about to enter adulthood.

Use neem oil right before the Japanese Beetles start mating.

Spread the oil on the ground near the afflicted plant. The oil and oily residue will get on the beetles and spread to the bugs as they leave their home underground.

Beetle on a pink flower petal.Pin
Photo Credit: Instagram @candidmobiletales

Also, applying this oil will permeate any developing eggs laid by females, resulting in the larva dying before adulthood.

Using natural Neem Oil isn’t the quickest fix, but it is still useful, and even better, it’s safer to use. One downside of using Neem Oil is that it is harmful to fish.

Avoid using this product if you live near a body of water, like a pond or river, as the oil can leach into the water source.

Soapy Water Solution

If you’re an environmentally conscious individual, this is a great way to eliminate Japanese Beetles in your Knockout Roses.

Mix a teaspoon of dish soap with a quart of water and spray the mixture using a spray bottle on the affected roses and the ground around where you see beetle damage.

Related: What’s a Good Knockout Bug Spray?

You can also hand-pick them and simply frown them in a bucket of soapy water. This is still the most effective way to control the population. 

Just ensure to start in the early morning, as this is the time when Japanese beetles are most active.

Green beetle on a pink rose.Pin
Photo Credit: Instagram @trishaagough

Pheromone Traps

These traps are among the least harmful options to adult Japanese Beetles. The Japanese beetle traps can lead the beetles away from your garden plants and encourage them to take a trip elsewhere.

All you have to do is place these traps as far away from your roses as possible, and voila!

A significant issue with traps such as these is that if they are placed too close to where Japanese Beetles already reside, they will do more harm than good.

Beetles will follow the pheromones wherever they sense them. If the trap is close to other beetles, it will act like a jamboree and attract even more beetles to the affected plant area.

Beetles clustered on a plant leaf.Pin
Photo Credit: Instagram @gardenhandswi

Beneficial Insects

Another great way to eradicate Japanese beetle grubs and keep their population in check is to introduce natural predators such as birds and parasitic wasps. 

Introducing beneficial nematodes will also kill the grubs and reduce the population.

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