Japanese Beetles have descended on the Chicago area. Half-inch to three-quarters of an inch long, with an iridecent green head and copper colored wing covers, they are here in greater numbers than usual due to our mild winter and the hot, dry summer. They eat many different kinds of plants, most notably lindens, crabapples, cherries, birch, roses and many perennials and annuals. They will skeletonize the foliage and eat the petals off the flowers. After they have devastated the garden, their grubs will live in the lawn, eating the roots of grass plants and causing severe dieback of the turf. They are difficult to control because they are so numerous and new ones keep hatching.
How to control them? They can be handpicked and dropped into a jar of soapy water, or sprayed with chemical-based insecticides. We have found success controlling them with neem oil. Neem oil is derived from the Neem tree found in India, where it is valued for its many uses. It is available as an organic spray that is as effective as anything we have tried; it may need to be applied weekly but it also works on other insects and fungus as well. Lawns should be treated with an insecticide such as Merit as soon as damage is noticed, or if your lawn has had grubs in the past. There is also an organic control called Milky Spore that can be applied to the turf, but it takes about three years to build itself up in the soil in sufficient amounts… so if you have grubs you will need to treat with an insectide or risk losing your lawn.
New beetles keep hatching out for weeks, so be vigilant during July and August. Your garden deserves to be protected from these pesky pests.