Information on Repelling Japanese Beetles (and their grubs)

Japanese beetles eating plant foliage

When it comes to repelling Japanese beetles, the more information you have, the better. From food sources to life cycle and beyond, once you know how to deal with them at every stage, you’ll be prepared to take them on – and win.

Food for Thought: What do Japanese beetles eat?

Japanese beetles feed on almost 300 species of plants. And as anyone who has had them invade their roses can attest, they can decimate otherwise healthy rose bushes. These beetles begin their month-long feeding and mating frenzy around mid to late June, which is when they defoliate our prized plants.

Japanese beetles generally stick to a 1 – 2 mile area if the food source and egg-laying conditions are favorable. A single Japanese beetle won’t do a lot of damage. But they generally congregate in larger groups. They work from the top of a plant downward and preferring to feed on plants in full sun locations.

The life cycle of the Japanese beetle starts as soon as adults emerge and begin to mate. Females burrow into the ground in the afternoon and lay 1 to 4 eggs every 3 to 4 days. The eggs hatch to a larva (or the familiar white grub stage) where they continue to develop for 10 months. Grubs prefer moist soil with lots of organic matter. And they especially love tender grasses. They are drought tolerant. Meaning that they will move deeper into the soil during scorching late summer heat. It is during this feeding period they can do the most damage to your lawn grasses.

Beetles overwinter in this grub stage, moving deeper yet into the soil to withstand any cold weather. They become inactive when the soil temperature drops below 50 degrees. Many birds such as starlings, common grackles and crows will eat grubs in heavily infested areas. A sure sign of infestation is a large flock of starlings digging up the grubs with their long, pointed bills. O r crows pulling up small pieces of turf as they dig and search. Moles, shrews and skunks will also feed on grubs.

When it comes to solutions, go natural!

There are chemical methods of killing both the grubs and adults; however, we prefer using safe, natural methods of combating these destructive pests. These natural methods are easy to use, work quickly, and don’t harm the environment.

Milky Spore

A natural method of grub control is milky spore. The spores will kill the Japanese beetle grubs in your lawn. Although it will not stop the flight of adult beetles.

Cedar Oil

The best safe way to deter adult beetles from your property is a cedar-oil-based insect repellent. Its odor is noxious to beetles and other pests, and it is an all-natural way to repel them. And if they stick around, it will shut down their receptors, and they’ll eventually leave or starve and die.

Shaking Japanese beetles into a bucket of soapy waterDo it by hand

Another easy, natural way to control the adult Japanese beetle is hand collecting. This is best done early in the morning when the beetles are the least active. Reducing the numbers on a plant makes it less attractive to other beetles flying in. Shake or knock them into a bucket of soapy water to kill them.

A word about traps…

We don’t recommend the use of Japanese beetle traps for home landscapes. They should be limited to large open areas away from valuable plants. This is because the powerful attractant can actually draw more beetles into an area. We also don’t recommend toxic insecticidal sprays and dusts to protect ornamental plantings. These can unintentionally spread to food crops, and they can harm our precious pollinators like bees and butterflies.

The Best Option: Diatomaceous Earth

Another extremely effective way for repelling Japanese beetles and their grubs is Food Grade Diatomaceous Earth. It works through a physical, non-chemical process of destroying the exoskeleton of pests. It’s like tiny shards of broken glass that cut through their protective outer shell and cause them to dehydrate. It’s non-toxic, and is even safe if ingested by warm-blooded creatures. It can be sprinkled liberally on plants and on the soil. Be warned, though, that it can harm pollinators if they land on it. So it should be used only on plants that don’t attract bees and butterflies. It should still do a terrific job of controlling the unwanted beetles, even if it’s used away from flowering plants.

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14 Comments

  • Reply
    Samantha
    July 24, 2008 at 4:19 am

    How can I tell if the grubs in my yard are Japanese beetle or some other type of beetle?

  • Reply
    jstutzman
    July 26, 2008 at 10:23 am

    Grubs are the larval stage for many types of beetles in the scarab family–not only the Japanese Beetle but May and June Beetles, Asiatic garden beetles and brown chafers. The most obvious identifier for the grubs versus other larvae that live in your yard is their whitish coloring and C-shaped bodies; after that you have to get pretty up-close and personal to the grub to distinguish between the different species by sight. So to know if you are treating just the Japanese Beetle larvae, you have to really know the life cycle.

    Japanese Beetles will emerge from the larva stage in early June, eat your lovely flowers and shrubs and mate until late July. Their adult life span is only about six weeks long, during which time the female will continually lay eggs. These eggs will hatch around August into the larva or grub stage and it is then they do the most damage to your lawn. They are eating voraciously to develop enough food storage to over-winter deeper below the surface of the soil. This is also the time when your lawn can be most stressed from the heat and drought of summer. The appearance of large brown spots, a large number of birds feeding on the lawn, or moles burrowing in your yard could be a good indicator of their presence. By September the grubs will be finishing feeding and will move deeper into the soil for the winter months and not appear again until about mid-April. Therefore any chemical treatment is only effective during the times that the grub is feeding, and is best applied in the fall feeding cycle; treating any other time is a waste. A non-chemical means of control includes the use of a bacterial disease called Milky Spore and it infects the blood of the grubs. This process is slower, but it is not harmful to people, other insects or animals.

  • Reply
    Dina Patel
    September 21, 2009 at 11:03 am

    i have grub problems when is it best months to apply grub application and what to apply and what month please.

    • Reply
      jstutzman
      September 22, 2009 at 8:14 am

      You can apply Milky Spore any time except when the ground is frozen. It will start working as soon as it has been applied.

  • Reply
    T. Willis
    February 24, 2011 at 4:50 pm

    How long after applying Milky Spore should I wait to apply seed and fertilizer?

    • Reply
      jstutzman
      March 12, 2011 at 12:27 pm

      Milky Spore has not bad effects on see or fertilizer, you can apply immediately afterwards should you choose to do so.

  • Reply
    Pay DeProw
    July 18, 2011 at 12:20 pm

    I spray an Ortho mixture that says it will kill Japanese Beetles on contact, but they seem to like it. I have mixed 2 tablespoons of dawn dishwashing liquid, and that has helped tremendously. I also saturate the ground with this mixture & it seems to help. I collect by hand & put into a small amount of water & dawn & they die immediately; otherwise, they will swim around in the water for days until I put a drop of dawn — in a matter of seconds, they’re gone. Do you agree with this method?

    • Reply
      jstutzman
      August 2, 2011 at 11:22 pm

      As long as you can keep up with getting them removed before they start laying their eggs, it is a great way to control Japanese beetles.

  • Reply
    Jessica
    June 16, 2012 at 10:18 pm

    I have been using Diatomaceous Earth on my garden and haven’t noticed a difference in the effect on the Japanese beetles. I have used it minimually at first and have now started to use it more liberally with no avail. They’re devouring my pole beans!

    • Reply
      jstutzman
      June 19, 2012 at 7:25 am

      Jessica I would suggest switching to Neem oil. Sometimes the hunger overpowers their other senses.

  • Reply
    Faith
    June 24, 2016 at 2:47 pm

    I am using diatomaceous earth (food grade) this year we have HUNDREDS of those pesky little beetles. They are killing my roses. I have tried Neem oil and other things nothing is working! I live in a little community but they seem to be in only my lawn and garden! I am also the only one with roses. I will try to start hand picking them next just to cut down on them because they are still flying around covered in the diatomaceous earth 🙁 I don’t know what else to to i am at my wits end

    • Reply
      jstutzman
      June 27, 2016 at 2:04 pm

      Faith, sorry to hear about the beetles that are dining on your roses. The Diatomaceous earth will work, its just not instant. If you want another natural product, use NocDown III. Spray it on your infected plants and the beetles will leave. Wishing your the best! Joe

  • Reply
    Kim Downing
    April 12, 2020 at 5:56 pm

    When would be the right time to use Diatoaceous earth? I live in Denver, Colorado

    • Reply
      GrowJoy Plants
      September 15, 2020 at 3:33 pm

      Kim, DE is only effective when the beetles are walking on it, so it’s usually applied in June when they come out of the soil and start breeding. However, if you really want to reduce the population there is a product called Milky Spore you can apply now. Good luck!

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