They’re Baaaaaaaacccckkkk. The Japanese Beetles Return for the Season!

Yup, that’s right.  These adorable, shiny (OMG so Shiny!) beetles have started to return.  Even though they may be cute they can be highly destructive.  The Japanese beetles (Popillia japonica: Scarabaeidae: Coleoptera) are, as you might guess, a non-native species of beetle which made its way here a number of years ago and easily found a home in our turfgrass and other plants.

Japanese Beetle adults kicking back on my tomato plants.
Japanese Beetle adults kicking back on my tomato plants.
Japanese beetle getting fancy with his legs on my tomatoes. Careful there mister!
Japanese Beetle larvae “grub” From Wikipedia

Their larvae often know as “grubs” (pictured below) spend their time in grass and can be responsible for some pretty serious damage to turfgrass stands; home lawns, sporting fields, etc.   They are also known to feed on some ornamental tree and shrubs.  These areas can be managed a variety of ways from planting more resistant turfgrass and plant varieties, to the use of products like synthetic pesticides or biological control methods, most notably milky spore disease.  Left unattended, they can eventually cause major damage to the grass by chewing through the roots.  And it’s not just the damage that they themselves do that you need to worry about.  You also have to worry about raccoons and skunks coming into your yard and pulling up the grass to get at those squishy, tasty grubs!  Remember Timon and Pumbaa from The Lion King!  They weren’t joking.

Timon with a tasty morsel. I think that would most likely be a caterpillar but it’s hard to tell with the way it’s drawn. Could just be a slug with a headcapsule…which isn’t really a thing.

These guys overwinter in the larval stage and the adults start to emerge right about now (June – July).  The adults damage plants in a very different yet just as important way.  I’ve been finding them on my tomato plants but this isn’t one of their typical plants they go for.  To be fair, I haven’t seen them feeding so it is possible I’m just noticing recently emerged adults just hanging out on my plants waiting to fly to bigger and more tasty pastures.  The adults are skeletonizers and will eat the “meaty” bits of the plant leaves, leaving the veins intact.  They are known to happily feed on over 400 species of broad leaf plants so take your pick.  A big one that they like are grapes and this is another thing that makes them a huge potential pest.  Imagine these guys in Wine Country!?!  Please, say it ain’t so!  Not my wine!  Infested strips of grass near a winery could be potentially devastating if left uncontrolled.

So how do we deal with these guys?  Well, I keep a nice plastic container in my freezer for all of the adults I find and I just throw them in there.  This is by no means an effective method of control but it’s a great method for just collecting some beetles.  There are a couple of traps that you can buy which use pheromones to attract the beetles to the bag where they fall in and die.  The problem with this is that they ATTRACT the beetles to the general region which can actually result in a bigger problem overall.  I actually want to get one of these bags so I can snag a whole bunch of bugs, but then I will have to worry about treating my lawn somehow…I wonder if I can get my landlord to pay for that???

Bag-a-Bug. Only really effective if you want to bring more Japanese beetles onto your property.

Other, more successful control methods are chemical treatments formulated specifically for “white grubs”.  “Grubs” is a term generally reserved for the larvae of scarab beetles which also includes Masked/European Chafers as well as the June beetles.  They all will survive in the turf during their larval stages but as you might imagine, will have different points of high susceptibility to treatment.  If you know you have mostly JB’s then make your application according to their life cycle.  The latter instars (juvenile stage) and adults are the least susceptible to pesticide products (synthetic and organic) as they are a bit more hardy by that time.  The best time to treat is when the larvae are still in their first couple of instars.  In Ohio, this means late August to early September at the latest.  As many as 95% of the eggs will be laid by mid August here.  By early fall when the weather starts to cool the grubs will crawl a bit deeper into the soil and begin their hibernation state and thus no longer be susceptible to treatments.

Japanese Beetle life cycle in Ohio. Remember to make your treatments when they are most vulnerable, in those early instar stages.

If you’re like me and you want to do your home gardening a little more on the “green” side when possible there is some good news and some bad news with regard to grubs.  The good news is there are some parasitic wasps (Tiphia popilliavora and T. vernalis) which are fairly well established in the Eastern states and will parasitize the larvae.  The bad news…they aren’t really effective at controlling the beetles in this area.  They are more successful in the southern states though.  There is also a disease called Milky Spore Disease (Bacillus popilliae) which is thought by some to be useful but depending upon your region it may or may not be.  The problem here is that this disease is already present in much of the natural habitat of these beetles and therefore populations (at least here in Ohio and nearby) have already been exposed to this and similar diseases.  By introducing the milky spore to an area where it is already present you’re not going to see much success as they have already been exposed.  In the areas where it has been effective, it can take a few years (2-3) for the spore count to build up to an affective level.  Don’t use any insecticides against the grubs during that time as the grubs are needed for completing the bacterium cycle.

Other than habitat modification (slit-seeding and planting resistant grasses and ornamentals) synthetic pesticide treatments are going to be your best bet.  I can’t recommend one particular product over others but by contacting your local Entomology Extension office they can give you the heads up on which products are best.

Hope that helps some of you.  Until next time! Hakuna Matatta!


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