Geraniums may help deter Japanese Beetles
In 1929, it was discovered that a natural control for adult beetles is, believe it or not, geraniums. The beetles feed on the geranium leaves and flowers, which puts them into a narcotic state for 12-18 hours. They lay on their backs while enjoying their altered state, which makes them susceptible to predators and easy for gardeners to collect and crush. Some beetles ingest the irresistible geranium leaves so often that they die from it.
But don’t interplant geraniums around your roses, thinking that this will deter the pests. Because Japanese Beetles love geraniums so much, interplanting will create the opposite effect and attract so many beetles that your roses will become infested. Plant a patch of geraniums in a sunny place far away from the plants you want to protect – it’s believed that the sun has an intensifying effect on the narcotic substance in the geranium leaves.