Japanese beetles on roses

A Remedy for Japanese Beetles

In Blog, Feature, Gardening, News by Val Thies16 Comments

The Japanese beetle is an unwanted garden pest causing massive damage to our beloved plants in its adult form and our lawns in its larval/grub form.

The Japanese beetle is not native to Minnesota and has no known predators in its adult stage, making it difficult to get the large numbers of these destructive beetles under control. They are voracious eaters, destroying leaves, flowers, vegetable plants, and fruit trees. You have probably seen one of their meals of skeletonized leaves in your own yard.

Once they are done feasting on your precious plants, the females fly off to lay 1 or 2 eggs in a sunny turf location. Over the course of their adult life, a female Japanese beetle will lay between 40 and 60 eggs. These eggs hatch in August and immediately begin dining on the roots of the turf grass where they were laid. The damage to our lawns by the larval or grub form of the Japanese beetle can be more devastating than the visual unsightly defoliation caused by the adult beetle. As the grubs feed on the roots of grass, they leave irregular shaped brown patches that lift when pulled on. This damage is usually seen in late summer or early fall. Grubs also attract animals such as raccoons, skunks, and moles which dig up our lawns in search of their next meal.

Beneficial Nematodes

So what can we do to manage these pests without the use of pesticides and chemicals? Beneficial nematodes to the rescue. Nematodes are beneficial microscopic insects that travel below the surface of the lawn and attack Japanese beetle grubs. They kill the grubs in 16-48 hours by locating the grub, entering it and infecting the pest with toxic bacteria and killing it. They produce hundreds of thousands of offspring which then search for more pests to infect.

They are safe for people, pets, and plants. They are a natural and effective alternative to chemical pesticides and have no detrimental effect on non-target species such as ladybugs, earth worms, and other helpful garden insects. Please note: This product doesn’t affect the adult beetles that are currently terrorizing your garden. It will reduce the overall population of beetles. Do not use beneficial nematodes if you have already applied an insecticide to your lawn.

August through September is the time to apply beneficial nematodes to your lawn.

Do Your Part: Buy Nematodes!

Tonkadale sells two sizes of nematode packages that you can apply to your yard. Buy them online through our website, then print out your confirmation email (or bring it on your smartphone) and pick up your nematode packages in the store.

Learn more about beneficial nematodes, including prices and application instructions.



  1. Yes, I would like to get the nematodes. How wonderful! Please put me down for some

    Thank you
    Vickie Kingston

  2. I now live in WI but am a fan of Tonkadale. We are coming for a wedding on 8/18 but since you said they would not be available til 8/17 I thought 8/18 would be OK.

  3. About 3 weeks ago I noticed the dead patches on my lawn from the grubs and had my lawn service apply insecticide. They also do any annual grub control in early summer. If I switch to nematodes, when would I apply them? Thanks

    1. We do not recommend using nematodes if you have already applied an insecticide, as it might kill the nematodes.

  4. Once I pick up the nematodes how long do I have to put them on the lawn? And if thunderstorms are predicted should I wait.? I have some reserved for This Friday but now they are predicting storms. Thanks,

    1. If they’re unopened, they can be stored in the fridge for several months. After you open them and mix them in water, they should be used right away. As for the rain, you could apply them before or after. You’ll need to keep the turf moist after application so the nematodes can do their thing, so if you apply them before it rains, it should be fine.

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