Japanese beetle news

Judith Adam

Geranium petals may thwart Japanese beetles. Photo by Heather Hayden

Stop the press — there’s encouraging news about Japanese beetles! You may know that from time to time, I go off on a rant about Japanese beetles and the amount of damage they do to roses. Nothing legally available will stop their progress through satiny, scented rose petals, and they also feed on nearly 300 other plant species.

The USDA Agricultural Research Service has been conducting experiments in conjunction with Rutgers University in New Jersey on the pesticide effect of annual geraniums (Pelargonium zonale) on Japanese beetles (Popillia japonica). To quote the study, when geranium petals are eaten by the beetles, “…within 30 minutes of consuming the petals, the beetle rolls over on its back, its legs and antennae slowly twitch, and it remains paralyzed for several hours. When paralyzed under laboratory conditions, the beetles typically recover within 24 hours, but they often die under field conditions because predators spot and devour them.” This is wonderful news, and gives gardeners a fighting chance to save their rose and hollyhock flowers.

Research has shown flower colour doesn’t matter; all contain the paralyzing agent. It’s simple enough to purchase beautiful geraniums, and put them in containers or in the ground near roses and other plants attractive to Japanese beetles. For instance, the beetles relish plum trees (and eat the foliage), so surrounding a plum tree with a ring of geraniums is a good idea. We must keep in mind that predators are required to eat the temporarily paralyzed beetles. Providing a birdbath or two in the garden (I have three!) will ensure birds nest nearby, and their fledglings will be very hungry for beetles. Many times I’ve seen mother cardinals carrying a big beetle back to their nests.

So there you have it—provide water for birds and geraniums for beetles, and beautiful roses may be yours.


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2 thoughts on “Japanese beetle news”

  1. Hi Karen (March 7),

    There’s no mention of harm to predators, including birds. The chemical in pelargonium petals temporarily paralyzes the beetles, and they recover within 24 hours. Considering the body mass difference between the size of a beetle, compared to a medium-size bird, the bird wouldn’t get a large amount of the effective element. But then, it could be very specific to beetles, and with no consequence for birds at all. Here’s a link to the information, if you’d like to see it: http://www.ars.usda.gov/is/AR/archive/mar10/garden0310.htm.

    — Judith


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