If you have a small Japanese beetle invasion, or you’ve decided not to use an insecticide, there are some tips you can utilize when hand-picking them.
First, the JB response to disturbance is to drop straight down from the plant. You can position your bucket of soapy water beneath the branch you’re tapping and use their own behavior against them to garner more direct hits into the water.
Is there a time of day that is more effective than others to handpick the JB? Yes! A study by Switzer and Cumming, 2014, found that handpicking JB at 7:00 in the evening had the equivalency of handpicking them 3 times a day.
Japanese beetles aggregate because of plant-emitted chemical compounds that have a fruity or floral odor. These plant communication chemicals are defenses emitted when plants are under attack. But these same odors have the detrimental consequence of signaling to Japanese beetles “party at the Smith linden!” When JB populations are kept low, plants emit less of the chemical compounds that attract more beetles to the site and the plants suffer less defoliation.