If it’s late summer in Ontario, it’s time for Japanese beetle mania. It sure is in my garden. Popillia japonica has a voracious appetite for over 300 plant species but that’s not the reason why they’re so annoying. No, for suburban gardeners dealing with the classic yin-yang of flower beds and lawn, it’s that wicked one-two punch these beasties deliver. As larva they feed on roots. As flying adults, they feed on just about everything else above ground. That means in the spring, just before they finally transform from grub to bug, they’re very likely happily munching away just beneath your lawn–the roots of good quality, irrigated turf grass is a favourite of these critters. Then, during the adult Japanese beetle’s “flight period” (from June 15 to September 30 in Canada), they wreak havoc above ground, defoliating just about everything in sight.
Google how to get rid of Japanese beetles and all kinds of suggestions bubble up but the consensus amongst horticulturalists, agriculture experts and researchers seems to be that drowning them in a bucket of soapy water is the most effective. To do this, you simply pick them off the plant and drop them into the bucket or shake the stems so they fall off into the bucket. You’ll see traps advertised for them but the pros all agree that you may catch some of the little buggers but you’ll also attract more from farther afield. Using nematodes on your lawn to get rid of them in their grub stage is also highly recommended.
Is there a more let-Mother-Nature-do-her-thing option? Yes and no. In Bringing Home Nature, Douglas W. Tallamy writes that there are a few North American insects that eat Japanese beetles but, because we have such little biodiversity in our urban areas to support native insect life, there are too few of these good guys to make any impact on the gazillions of Japanese beetles that reproduce each year in our famously un-diverse gardens made up of non-native plants and monocultures known as lawns.
So the scourge of Popillia japonica isn’t going to go away any time soon but you can be proactive and choose plants for your garden that don’t appeal to them. According to Michael J. Raupp, aka The Bug Guy, a Professor of Entomology at The University of Maryland, there are some plants that seem to do better at avoiding the big munch.
- Roses with small, dark-coloured blossoms tend to avoid the beetles whereas roses with larger, light-coloured blooms do worse.
- Maples with dark leaves (purple or deep red) faired worse than those with green leaves.
- Lindens have hairy leaves so they aren’t as popular with the beetles as trees with leaves that aren’t hairy.
Also, check out The University of Kentucky College of Agriculture’s list of landscape plants likely to be attacked by adult Japanese Beetles. You’ll also find a short list of plants seldom damaged by them.
But these lists aren’t explaining why some plants can get obliterated while other plants are seemingly ignored. For instance, at this very moment, my Cigar plant (Cuphea hybrid) is being decimated by the critters while, crammed in the same container, the Campfire™ Fireburst Bidens hybrid plants (a new Proven Winners introduction for 2016 that I’m trialling) are being completely ignored. Is this because Proven Winners has bred a new super plant with an invisible force field that protects it from the beetles? That would be cool but I doubt it. The Bug Guy explains:
“You may have noticed that Japanese beetles often attack one plant severely, leaving a lucky neighbor relatively unscathed. Apparently, when beetles initiate an attack, specific odors are released by the damaged plant. These send a signal to other beetles something like “good food, eat here”. This foliar attractant is compounded when female beetles release a chemical message called a sex pheromone. The sex pheromone says to the guy beetles, “how’d you like to spend a little time with me?” A rambunctious love fest and feeding frenzy erupt, and, in the process, your plant takes a beating.”
You gotta take your hat off to anything that can multitask so enthusiastically and effectively. That said, I need to go find my bucket.