This column ran originally July 21, 2018.
Gardeners from all over have been posting on Facebook about the invasion of Japanese beetles, an insect that has been only a minor pest the last several years.
“Oh my gosh yes,” said Kate Franzman, farmer and beekeeper at Public Greens: Urban Kitchen with a Mission in Broad Ripple. “They are on just about everything. When I get there in the morning I walk through the garden with a container of industrial dish washing liquid from the kitchen and push them into it. In general, the bugs have been unreal this year.”
Purdue’s Japanese beetle report
For sure, the leaf- and flower-eating, metallic green beetles appear to be back in record numbers. Even Cliff Sadof, my go-to Purdue University Extension entomologist, issued a report late last month about the influx of the beetles.
“Although the reasons for this resurgence are unclear, part of the story is that for the past few years there has been enough moisture in the soil during the mid summer egg-laying period to allow most of the beetle eggs to hatch into grubs. These grubs flourished and grew into the adult beetles that emerged the following year, he wrote in the Purdue Landscape Report newsletter.
Warmer temps enable emergence of Japanese beetle grubs
This year’s warm temperatures have allowed the grubs to develop and the beetles to emerge and dine on our plants. Japanese beetles prefer members in the rose family, which includes roses, many fruit trees, hibiscus, grape and dozens of other plants.
“They are devouring some of my roses, the ones they love the most are the yellow ones,” said Teresa Byington, president of the Indianapolis Rose Society. She has at least 175 roses on her Hendricks County property. “I have also seen them voraciously attaching the zinnias this year. Ugh!”
Beetle infestation may be spotty
Japanese beetles rarely, if ever, uniformly infest a landscape, Sadof said. “There are always areas with heavy damage and areas with light or no damage at all.”
There are several insecticides that can be used against Japanese beetle adults, Sadof said. “It can be difficult to kill the beetles without harming pollinators that visit flowers, because most insecticides that kill beetles will also kill pollinators.” Reducing the number of applications is one way to protect pollinators. If you decide an insecticide is the way to go, wait to spray until you see several gathered on the plant, rather than just one or two, he said.
Japanese beetle controls
Byington does not use insecticides. “My only defense is to knock them into a bucket of soapy water. Squishing them or leaving their destructive remains only signal for others to come. We have lately been encouraged by reports that many of our birds are now taking a liking to them. Hopefully in time that will help us with control.”
- Don’t allow the beetles to congregate in great numbers on the plant. A high concentration of beetles alerts their kin that everyone’s welcome. Knock them into a bucket of soapy water.
- Remove any heavily damaged leaves, again, because these serve as calling cards for more beetles.
- For more information, view or download Purdue’s Japanese Beetles in the Urban Landscape.
In my own garden, I’ve seen about a half dozen beetles. Two Japanese beetles on pink SunPatiens were flicked into a can of soapy water for their demise.