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Japanese Beetles on the Prowl

Posted by Kari Houle - Articles

Over the weekend the Illinois Pest Survey shared a post on Facebook saying that Japanese Beetles were out in Central Illinois. Sure enough, I go and check the growing degree days for the area and they are at the point when Japanese Beetles begin to emerge. If you want to know more about growing degree days, I wrote an article about it back in 2015 and you can find that article here: http://go.illinois.edu/GrowingDegreeDays

I've had people asking will this year be as bad as last year and it's hard to say. Sadly, it's a wait and see situation and keeping fingers crossed that what seemed like a never ending winter helped to cull part of the overwintering grub population. I've also been asked how we can prevent Japanese Beetles and there really is not good answer to that either, we simply can't and we are at the mercy of Mother Nature.

A few quick Japanese Beetle facts.

  • They fly 10 to 15 miles, so even if you are using grub control on your turf (only recommended when they are causing damage when populations are around 10-12 per square foot), it only works to prevent them from turning your lawn into a roleable carpet.
  • Japanese Beetle traps only work to increase the party in your yard. They are scent based and attract more beetles to your yard. You may dump the trap full of beetles on a regular basis, but most get side tracked by much tastier morsels in your yard. Some research shows that traps are only effective when placed ¼ mile away.
  • They feed on over 300 different types of plants with their favorite diners being Linden, Roses, and Brambles.
  • They prefer laying eggs in turf that's green and growing, so it's honestly better to let turf go dormant during the heat of the summer so it reduces preferred egg laying sites.
  • Japanese Beetles aren't new – they were first discovered in New Jersey in 1916 so they've been munching away here for over 100 years.
  • Adult Japanese Beetles live for 30-60 days and females lay between 40-60 eggs in their life time. Prolific aren't they?
  • There are chemical controls for Japanese Beetles, but keep in mind that all of those labeled for use are toxic to highly toxic to pollinators, so caution is needed if you choose to apply to flowering plants attractive to pollinators.
  • Another option for control is knocking them into a bucket of soapy water. It's a great way to get frustrations out by knocking those suckers in one by one. Friendly reminder – just remember to dump the bucket out once they have expired, because a bucket of dead Japanese Beetles in hot summer heat over a few days does not smell so pretty.
  • The good news is, there are plants out there that are not favorite diners for Japanese Beetles. A few examples include Lilac, Dogwood, Magnolia, Forsythia, Redbud, Holly, Sweet Gum, and Tuliptree.

For more information on Japanese Beetles you can contact your local Extension office. You can find your local Extension office in Illinois by visiting this website: https://web.extension.illinois.edu/state/findoffice.cfm



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