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Pelargoniums against Japanese beetles?

20160517A Maverick Mix Park Seed
Deadly to Japanese beetles, pelargoniums create a beautiful barrier around other plants. Photo: Pelargonium x hortorum ‘Maverick Mix’, Park Seed.

Not that I want to scare you, but… Japanese beetle (Popillia japonica) season starts in late June/early July and if this insect is a major pest in your garden (it is far from universal, only being found here and there in North America and Europe), there are plants you can put on your spring shopping list that can offer some control.

20160517B
Japanese beetle

For example, Japanese beetles are attracted to the smell of the zonal pelargonium, also known as zonal geranium (Pelargonium × hortorum). In fact, if given a choice, beetles prefer pelargonium flowers over most other plants. However, when they chew on its flowers rich in quisqualic acid, they quickly become paralyzed. They then fall to the ground, lying immobile on their back, where predators collect them or they die from desiccation. It’s therefore possible to surround susceptible plants with pelargoniums to reduce beetle damage or to plant pelargoniums in a separate flowerbed nearby. (Do not however interplant pelargoniums among susceptible plants: studies have shown that actually increases damage to them!)

Notice that the popular belief that only pelargoniums with white flowers are effective is false. You can use whatever color of pelargonium you choose to knock out a few beetles.

Other plants have the same effect: four o’clocks (Mirabilis jalapa), larkspurs (Delphinium and Consolida) and castor beans (Ricinus communis) are also known to both attract Japanese beetles and poison them.

You have to accept the fact that these trap plants will be a bit munched on, since the beetle has to at least taste them to be poisoned. But the spirit of vengeance is very strong among most gardeners and many will certainly feel a bit of collateral damage in their war against the Japanese beetle is a worthwhile investment!

20160517A Maverick Mix Park Seed

4 comments on “Pelargoniums against Japanese beetles?

  1. Aly Toledo

    Thank you for your article on japanese beetle. I won’t bother picking them out of my geranium flower pots anymore. I just wonder if you could shed some light on plum trees and black knot. I bought a plum tree from botanix three year ago. The tree has been attacked by japanese beetle every summer, I picked a lot of them off but they still manage to eat most of the leaves. And last summer the tree had black knots on it. I cut the aflicted branches off but not sure they’ll appear again. Should I give up on planting fruit tree or can my tree be saved?
    Thank you for your time and all your writing.

    Aly Toledo

  2. Pingback: Controlling Those #$@&%* Japanese Beetles – Laidback Gardener

  3. Unfortunately all these plants are popular or at least edible by deer so plant accordingly.

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