Japanese Beetle Late Summer Myths and Sensible Strategies

Damage to grape vines in my neighborhood

The unproven and varied strategies for managing Japanese beetles and their larvae each summer gets more and more interesting as they spread out and gain more dining opportunities along the Front Range. It is understandable that gardeners and homeowners are desperate for any fix to make them go away or reduce their numbers in yards. 

Let's face it, these insects are horrible. Most of us have no problem using another "H" word to describe our feelings. Hate, with a capital "T" and that rhymes with "D" which stands for Disgust, Detest and Despise. I could use stronger words, but this is a family friendly blog.

Those of us in central and south Denver neighborhoods who have been dealing with Japanese beetle summer invasions in fairly high numbers for five years or more can offer some sound advice as to what works or not. We've had lots of practice. Plus there are some newer resources from local CSU entomologists and Colorado Department of Agriculture experts with effective management practices and products to use on adults and lawns for larvae.

Our local experts and research universities know well what to recommend for Japanese beetle management. They've had the benefit of learning from other experts in these same fields who have been dealing with Japanese beetles for over one hundred years. Japanese beetles arrived in Riverton New Jersey in 1916. Hey, it only took them a little under one hundred years to make it to Colorado.

Here are some myth controls I've heard or read of late. I won't qualify the use of the first three bullets with how or why they are being used because I believe they could or will harm plants, the soil, beneficial insects pollinators and who knows what else. 

• Powdering plants JBs eat with baby powder.

• Dousing the whole lawn with diatomaceous earth.

• Eviscerating dead beetles in a food processor to make a slurry, then sprayed over plants as a repellent. Mix in catmint foliage (must be for fragrance to mask the horrific smell of dead beetles)... "and really...the kitchen Cuisinart food processor?"

Save your money - no traps!

• Putting out traps work (yes they work) - comments from me - "Do you believe a random posting recommendation on a local community Internet bulletin board or perhaps from a co-worker or a sales clerk in a garden center that putting up a Japanese beetle trap will reduce J. beetle numbers and damage to your plants? Or do you believe decades of researched university and agricultural studies that say that traps draw in more Japanese beetles to the area and surrounding plants? 
• The lures are highly attractive and will draw in beetles from long distances. Hmm, I smell fresh baked apple pie - and there's a la mode too. It's free pie, wonder how many neighbors will show up for a piece or two, then invite some of their friends to join the eating party. And then what happens - they never leave, just like cousin Eddy!
• If you buy into using traps then you should have very happy neighbors because their beetles will be coming to your yard and eating more of your plants. They should send you a thank you note or leave a bottle of wine on your front porch. Better yet, they ought to leave you a few bucks each week to cover the trap baits that you have to replace often. I wish I lived next door to trap users!!"
• Will plants like Virginia creeper serve as trap plants to keep beetles occupied and not interested in other landscape plants? The answer is highly unlikely, no. As the summer progresses and plant sources get eaten, they will seek out other plants they like (or will try) in the landscape. 
• If you plant onions right next to roses, will beetles leave roses alone? No, they know exactly where the roses are growing and will ignore the onions (or any other plants they don't like) and go straight for their preferences. Consider and research new plants added to your landscape carefully. Click HERE for my like/dislike plant list (a work in progress).  

What are the best controls to use now that it's mid-August on both adult beetles and larvae in lawns (next year's generation)?

• For the most immediate control flick adults into soapy water in the morning or evening when they are sluggish and easy to flick. Keeping the numbers down actually reduces more beetles from joining the eating party on your plants. What attracts them to plants are the plant oils released by beetle chewing (called congregation feeding), so less beetle chewing means less beetle visits. The research on Japanese beetles says that it is fine to squish or pinch adults on the spot. Their smushed parts do not attract more beetles to the area - it's the chewed plant oils that put out the welcome sign. 
• A good mail order, organic spray for adult beetles is beetleJUS!™ beetleGONE!^® Different names from different suppliers. 
• Try to mow less often - keep the lawn on the tall side which adult females don't like. Their preference for egg laying is moist, low cut grass. Keeping the lawn on the drier side during egg laying (June through August) is also effective on egg mortality. Just use care to keep any trees in or near lawns watered so they aren't stressed.  
• There are a handful of grub control products recommended, but get going, most of them are more effective when put down earlier in the summer. Organic Btg grubHALT!™ or grubGONE!^® can be used now into September, as can beneficial nematodes. 
• Don't waste your time or money on Milky Spore (scroll to page 7), it doesn't work well here, try GrubEX, nematodes or Btg. Click HERE for information on all grub products - found on Dr. Cranshaw's Fact Sheet.

Smile (but I should have sat up straight)

And when the final beetle has fallen dead sometime in September (hopefully) - smile. There is hope on the far horizon to battle this ravenous foe with beneficial predator insects and a new spore pathogen for larvae. Stay tuned and I'll write more as I learn more.