Japanese Beetles Make Their 2018 Debut

 

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The Japanese Beetle – pretty to look at but oh so destructive!

June is a glorious month in the garden, but it also the cue for adult Japanese beetles (Popillia japonica) to emerge from the soil. They’ll hit their peak from late June through at least August. I haven’t spotted the metallic green and copper devils in my garden yet, but if the past is any indication, they’ll visit soon.

Colorado State University offers this comprehensive fact sheet with everything we need to know to defend our plants. It’s an especially valuable reference when considering products which may or may not be beneficial in reducing the pests while doing minimal damage to the ecosystem. If there were best seller lists for gardener information, this would be on the top!

Here are important takeaways from the fact sheet:

05601-fig5Japanese beetles feast on foliage, buds and flowers of their favorite plants. Particularly susceptible are roses, Virginia creeper, Linden trees, Rose of Sharon, Japanese maples, Silver lace vine and Gaura are among their favorite targets. Tell-tale signs of Japanese beetle damage are a skeletonized pattern of mutilation on tender, new foliage and deformed flowers or buds. While unsightly, the damage will not kill the plant.

05601-fig8Traps are not beneficial. That yellow trap you’re tempted to hang in your yard is an open invitation for more Japanese beetles to visit. The trap won’t be able to catch them all and the effect is more, not less damage. Perhaps if your neighbor hangs one…?

Picking does help. Japanese beetles are easy to spot in the cooler parts of the day and can be coaxed into a jar of soapy water with a twig or a shake. Catching is preferable to squishing, as a squashed beetle releases a compound which lures more of their kind. While it may not be fun, catching is oddly satisfying!

Do insecticides work? As always, caution must be used to avoid damage to pollinators, especially when plants are in flower. Products containing pyrethrins, azadirachtin and acetamiprid – used in the early morning or at dusk – when bees and other pollinators are less active – are the safest. See the fact sheet for more details and follow all product recommendations carefully.

Consider removing temptation. Can you replace your Virginia creeper with something less enticing? Do you have roses that have struggled for years? Perhaps it’s time to replace with something less alluring. Conversely, when adding to your landscape avoid plants which are irresistible to this insect.

Late season turf damage. Each female Japanese beetle lays 40-60 eggs in her 4-8 week life span. Eggs are laid deep in moist turf soil. Since eggs and subsequent larvae thrive on moisture, keeping soil on the dry side will inhibit grub development and decrease turf damage. Grubs also munch on turf roots, so mowing at a higher height, which promotes vigorous roots, can help reduce turf damage.  More control ideas can be found in this fact sheet.

Have you spotted Japanese beetles in your garden yet?

 

Submitted by Linda McDonnell, a Denver County Master Gardener

 

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5 responses to “Japanese Beetles Make Their 2018 Debut

  1. Steve Aegerter

    You may want to try this – I have found that they adore my globe mallow, not sure which one I have – but it gets about 4 1/2 feet tall with a 3-foot spread and has pale orangish-pink blooms. Started from seed many years ago. At any rate, the Japanese beetles love them, but they never damage the plant one bit. They meet there for romance!! The damage to the rest of the landscape has been minimal – at least that has been my experience so far.

    I have a large mouthed jar, I believe it held cherries, half filled with water with a good squirt of liquid detergent. I merely go out daily or even twice and shake them into the jar – hence the need for the large mouth. I collected hundreds and hundreds last summer. I collected seed last year and started some for my clients.

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  2. Martha Pearse

    Hasnt the squishing/pheremone theory been disproven?

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  3. Steve Aegerter

    You may want to try this – I have found that they adore my globe mallow, not sure which one I have – but it gets about 4 1/2 feet tall with a 3-foot spread and has pale orangish-pink blooms. Started from seed many years ago. At any rate, the Japanese beetles love them, but they never damage the plant one bit. They meet there for romance!! The damage to the rest of the landscape has been minimal – at least that has been my experience so far.

    I have a large mouthed jar, I believe it held cherries, half filled with water with a good squirt of liquid detergent. I merely go out daily or even twice and shake them into the jar – hence the need for the large mouth. I collected hundreds and hundreds last summer. I collected seed last year and started some for my clients.

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  4. My first beetles today- on my flamingo willows! Horribly timely article…Last year it was June 3rd for my yard- so there were a few days extra. I’m off to spray the roses with cold pressed Neem with Azadirachta – and hopefully squeeze one more weekend before the plague…

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