Tagawa Gardens Blog

Japanese beetles are here to stay! How can we fight back?

I’d love to be able to tell you that if we work long enough and hard enough, one day we’ll eradicate Japanese beetles from the Colorado Front Range. I can’t tell you that because according to the experts, it won’t happen. The beetles are here to stay. That doesn’t mean we can’t fight back and make their lives as difficult as possible, because we can! The question is how best to do that.

No new magic bullets

Research is going on across the country, and progress is being made on new ways to try to mitigate the beetles’ damage. That’s great! But for here and now, one of the best ways to fight back is also one of the most environmentally friendly, and it’s virtually free!  Simply knock them into a bucket of soapy water. Japanese beetles naturally play dead and drop off of plants when they sense danger. Why not use that against them?

This easy approach can be surprisingly effective! A study by Eastern Illinois University shows that hand-removal of the beetles “significantly” reduces damage to plants. But the study has more good news. Removing the beetles in the early evening, around 7:00 dramatically reduces the number of beetles congregating or clustering on that same plant the next morning.  It has to do with a stress hormone the plants themselves release when they’re under attack.  The beetles will cue off of that strong plant hormone and be drawn there by the dozens when they begin flying again the next day.

The study shows that even if you remove the beetles just once a day, doing it at 7:00 in the evening is actually more effective than removing them three separate times earlier in the day!  That’s information we can use!

Want more weapons in your arsenal?

Adult beetles do the most damage, so let’s start there. In addition to hand removal of the beetles, there are both conventional/synthetic and organic treatments that can be used against them.  John is one of our Garden Advisors at Dick’s Corner. He pushes back hard on the idea of “controlling” the beetles. He prefers to think in terms of mitigating the damage once they arrive.

For organic control of the adult beetles, John recommends a product that’s been quite helpful since it came onto the market a few years ago. It’s called “beetle-Gone!”

The beetleGONE! powder is mixed with water and sprayed directly onto the plants where adult beetles are actively feeding or likely to feed soon. It doesn’t kill the beetles on contact.  It contains a bacteria that is deadly to Japanese beetles that eat treated vegetation. It’s a biological insecticide and will not harm insects other than scarab beetles, the family that includes Japanese beetles.

beetleGONE! is a little more expensive, but it can be quite helpful in our fight against this pest.

“Eight” is a conventional spray for the adult beetles

The insecticide Eight has been around for years. It’s main ingredient is permethrin which can be harmful to beneficial insects if not applied properly, but used strictly as directed, it will knock down Japanese beetle populations.

eight insect control at Tagawa Gardens Denver

Eight kills on contact and should be used primarily when the beetles are present and visible. It should not be applied when the weather is hot or windy when the spray could drift to nearby plants where beneficial insects like bees might be present. Be sure to read the label completely before using it.

Japanese beetles’ life cycle begins in our lawns

Female adult beetles each lay 40 to 60 eggs in their lifetime. Unfortunately, our love for lush green lawns comes gives them just the nursery they’re looking for:  the well-watered root zones of our turf grass.

japanese beetles root zone at tagawa gardens denver

In mid-summer, when the beetles are most abundant, female beetles stop feeding each day just long enough to lay eggs a few inches down into the soil beneath our lawns. The eggs hatch as grubs, then feed on grassroots over the summer. They spend the winter deep in the soil, then pupate in the spring and emerge as adults in late June or early July. The bacteria in grubGONE! can kill the grubs before they mature.

Use of grubGone! can also help struggling lawns that have Japanese beetle larva feeding on their roots. Package directions indicate the best time to apply grubGONE! is late July into early August.

For a conventional approach to killing grubs…

John recommends GrubEx, a granular pesticide that kills the grubs before they can emerge as adults.

GrubEx should be applied with a rotary spreader once a year, between May and August, which means that now is still a good time to put it down.

As always, read and follow the directions of the package to the letter. It’s the law!

Another organic option you may not have heard about

Beneficial nematodes are microscopic parasites that can be watered into your lawn to kill the grubs of the Japanese beetles in a way deserving of their own science fiction monster movie.  Nematodes work their way into the grubs’ bodies and then begin to poison them from the inside out. They are harmless to other beneficial soil dwellers.

As the directions on the package indicate, the nematodes are mixed with water and then applied to your moist lawn once adult beetles are present and beginning to lay eggs. It’s best to apply the nematodes in the early morning and late evening and avoid the hot mid-day sun.

Beneficial nematodes occur naturally and pose no threat to humans, pets, or beneficial insects.

Dick’s Corner is at your service!

Our ongoing fight against Japanese beetles can get frustrating.  Avoiding plants the beetles love is good advice, but with more than 300 plants on their menu, that can be hard to do.

For more advice, and maybe a bit of “we feel your pain,” please stop by and chat with Tagawa’s Garden Experts and Dick’s Corner.

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Luan Akin
About 
Luan Akin
Tagawa Gardens Outreach Ambassador

After 30 years as a news reporter for KCNC TV in Denver, Luan Akin was ready for a change. In 2008, she came to Tagawa Gardens and offered to create a brand new position: Garden Outreach Ambassador.

Luan had trained and volunteered as a Douglas County Master Gardener for ten years. In addition to her duties as a news reporter, working primarily out of the Channel 4 News helicopter, Luan also produced and presented a long-running series of stories called “Gardening Together.”

All these years later, Luan now works year ‘round, presenting a variety of gardening and nature-related topics to hundreds of children, HOA’s, gardening clubs, church groups, small businesses and other organizations.

She is an avid gardener, a beekeeper and a proud mom to four dogs who have trained her well.

6 Comments

  1. JD

    July 3, 2021 - 4:33 am
    Reply

    60+ years ago as kids in VA, the beetles loved the roses. Mother paid us to hand-pick the beetles off and into baby food jars…filled with gasoline..

    • Luan Akin

      Luan Akin

      July 20, 2021 - 1:23 am
      Reply

      J.D… Isn’t it amazing what kids can find entertaining… and in your case, profitable!!

      I live in the prairie east of Parker, along the Douglas/Elbert County line. The beetles are few and far between here because they’d have to cross a lot of grassland that offers nothing to eat en route to our small lawns, rose gardens and other tasty treats they love! And I’m hopeful to keep it that way!

      My best,

      Luan

  2. Noel

    July 7, 2021 - 2:06 am
    Reply

    What about the beetle bag traps? I’ve used them for years and have 3 full bags of beetles by the end of summer. I’ve heard it said that the scent attracts more beetles into your yard, but if more people would use them, it seems that significant numbers of beetles would be removed from the environment at no environmental cost. Every beetle caught in one rof these traps is not going to eat your plants or reproduce. I just wish more people would take the responsibility to trap beetles that way.

    • Luan Akin

      Luan Akin

      July 20, 2021 - 1:18 am
      Reply

      Sorry I missed your comment, Noel. The Japanese beetle traps trigger a lot of debate. The hormonal and floral lures are pretty powerful and will definitely attract and trap a whole lot of beetles. The debate is over whether they end up drawing a lot more beetles into your yard than you would have had otherwise, but not catching all of them, so you end up with more beetles than if you hadn’t used them. CSU recommends them only for monitoring… to let gardeners know when the beetles have arrived.

      However, I know several experienced gardeners who use them simply to kill as many beetles as possible. If you do use them, they need to be at least 30 away from desirable plants, and emptied on a regular basis. Hanging them from a shepherd’s hook away from their favorite plants is one suggestion.

      Not a tidy answer, I know. It’s one of those techniques that comes down to each individual gardener’s decision.

      Hope that helps.

      My best,

      Luan

  3. Jamie Luisi

    July 16, 2021 - 5:59 pm
    Reply

    Do you have organic option for budworms on petunias & other flowers? Thx

    • Luan Akin

      Luan Akin

      July 20, 2021 - 1:31 am
      Reply

      Jamie… There are a couple of organic products you can try. Tagawa’s carries both of them.

      One is “Bt.” It comes in a sprinkle-on powder or a spray. The spray is probably a better choice for flowers since the powder is a bit unsightly for that use. Bt is a naturally-occurring bacteria that is toxic to the digestive tract of caterpillars but perfectly safe on beneficial insects. Also won’t harm birds that eat the caterpillars as they hang on the plant for a day or two until they fall to the ground.

      Another organic product to consider is called “Captain Jack’s Dead Bug Brew.” It’s useful and works well for a lot of things and is one of my go-to’s when I need a pesticide.

      Obviously, follow the directions on both products. Even “organic” pesticides can cause problems if they’re not used correctly.

      Hope that helps!

      Luan

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