Answer: Purple leaf plum and roses are two of the Japanese beetles favorite foods. They also love grapes and other fruit trees. But they don't limit themselves to just those. They will attack almost any plant!
Although Sevin (carbaryl) is often recommended for Beetles, it will also kill other beneficial insects such as bees. Organic/environmentally conscious gardeners may prefer to use the Neem products which act as a repellant.
Use of the traps is in controversy, some saying they attract more than they catch.
A government written document on the beetles is available on line at http://www.aphis.usda.gov/oa/pubs/jbbro.pdf It gives some good info on the beetles, including plants which are resistant to them.
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