Has there been any improvement in the technology for removing Japanese beetles? We have rosebushes and a large grapevine, and by August we’re inundated with Japanese beetles. When my father had them, it was our daily duty to pick them off and put them in a can of kerosene.
Your father had the right idea by collecting Japanese beetles every day, because it stops signals given off by feeding beetles that attract more beetles: Handpicking can reduce overall feeding by half. But instead of kerosene, a couple of inches of soapy water in a pail or bowl is the collection method generally recommended. First thing in the morning, hold it under the leaf or bough where the beetles are feeding, and brush them down into it with your hand. The beetles won’t bite you, and as long as temperatures are cool they will fall into the water rather than flying away. Within an hour, they will drown.
Other organic control measures include applying beneficial nematodes or milky spore disease to grass to kill white grubs (Japanese beetle larvae), and growing plenty of flowers that attract beneficial Typhia wasps, which feed on flower nectar and aphid honeydew. Another beneficial insect, the Istocheta fly, is hosted by Japanese knotweed.
Commercial traps often attract more Japanese beetles than they catch, so they should not be placed near cultivated plants. Japanese beetles can fly up to five miles, so even if you place traps far from your garden, you may be attracting and catching beetles that might not otherwise be present.
Japanese beetles feed for only six to eight weeks, and though roses, grapes and soybeans are among their favorite plants, they are able to feed on over 300 plant species. So, grab your bowl of soapy water, and make collecting feeding beetles a daily summer ritual.
— Barbara Pleasant, contributing editor