Every Monday we tackle common lawn and garden questions on Home Dish. Today we referred to expert Julie Weisenhorn, state director of the Master Gardening Program, University of Minnesota Extension. For more information about Master Gardening programs in your county, visit www1.extension.umn.edu/master-gardener.
Master Gardeners have been discussing whether geraniums are toxic to those pesky Japanese beetles, and if so, is there a benefit to interplanting geraniums around plants that the beetles prefer (such as roses or grapes).
I asked our expert, University of Extension entomologist Jeff Hahn. He said, “This is a real phenomenon; when JB feed on geraniums (Pelargonium spp.) they consume a toxin that, well, intoxicates them. This does not kill them, but they are paralyzed for hours. They eventually recover. Interestingly, they don’t apparently learn from this as they will commonly go back and feed on geranium again. There is research that shows that interplanting geraniums does not protect other plants. In fact, the research showed that there were more JB on roses when geraniums were present.”
— Julie Weisenhorn, state director U of MN Extension Master Gardener
Editor’s note: Japanese beetles can become a nuisance this time of year, destroying beautiful landscaping in a matter of days. One method of pest control is filling a bucket with soapy water, then knocking the beetles into the bucket. They are most sluggish in the morning hours, so this is a good time to hunt them down. If you hold the bucket underneath the beetles and attempt to touch them, they will often respond by playing dead and will drop right into the bucket, eventually drowning. Or—if you don’t want to touch them—use a butterfly net to catch them, then dip the net into the bucket. Leave the dead beetles in the bucket and set it outside. The bucket can serve as a repellant to other beetles. Happy hunting!