I’ve copied the original news release from the USDA here because I wanted to make sure you all saw it.
Summary: Japanese beetles don’t like Pelargoniums (annual geraniums) and if they eat the leaves, they tend to pass out. There is no current spray-product that mimics this action in JB but you can reasonably expect to see some action on this in the future.
Controlling Japanese Beetles On The Home Scale With This?Home scale: If you’re of an experimental kind of person, I’m sure you’re thinking it might be possible to concoct a geranium leaf tea as a spray Probably a cold soak as hot water might kill the active ingredient) I have absolutely no idea how this might work – kill, avoidance etc. And more importantly, I have no idea if this kind of product might be of any danger to you or your pets – so I can’t recommend you do it in any way. But I know in the next little while you’re going to read about folks trying it and it will likely appear on forums etc. as a “magic cure” for this voracious pest.
You’ll Likely Read About How Geraniums Will Now Control Japanese Beetles
You’re also likely going to read how just planting geraniums will protect your plants but if when you read the article you’re going to see how this isn’t necessarily true (the leave stun them if eaten – not kill or deter)
This one falls into the category of “now you know the truth” and won’t get you going down some beginner-gardening pathway with wrong information.
This is from the USDA March 2010 issue of Agricultural Research magazine. Interesting information for gardeners.
Geraniums Could Help Control Devastating Japanese Beetle
Geraniums may hold the key to controlling the devastating Japanese beetle, which feeds on nearly 300 plant species and costs the ornamental plant industry $450 million in damage each year, according to scientists with the Agricultural Research Service (ARS).
The beetle, Popillia japonica Newman, can feast on a wide variety of plants, including ornamentals, soybean, maize, fruits, vegetables. But within 30 minutes of consuming geranium petals, the beetle rolls over on its back, its legs and antennae slowly twitch, and it remains paralyzed for several hours. The beetles typically recover within 24 hours when paralyzed under laboratory conditions, but they often succumb to death under field conditions after predators spot and devour the beetles while they are helpless.
ARS entomologist Chris Ranger at the agency’s Application Technology Research Unit in Wooster, Ohio, is working on developing a way to use
geraniums to control the beetles.
ARS is U.S. Department of Agriculture’s principal intramural scientific research agency.