Japanese Beetle Control on Leaves and Flowers

Biology and Life Cycle—one-year complete life cycle from egg, larva, pupa, adult. Adults usually emerge in June, females begin egg laying immediately and in to September. Each female lays up to 60 eggs as an adult (not all at once) in nearby grass turf, they seek well-irrigated areas. Cool-season grasses like Kentucky blue grass, ryegrass and fescue are their preferred turf for egg laying. White Grubs live in turf roots – fall, winter, spring, emerging as adults in June for the cycle to begin again.

Japanese beetles are attracted to over 300 plant species and will eat grass roots, leaves, fruits and flowers of many ornamental plants plus agricultural plants. They are very mobile and will fly to plants they prefer, up to five miles. The volatile oils released from chewed plants attract more adults to those plants. They are very actively feeding, mating and egg laying in the heat of the day. They begin feeding at the tops of plants. In the cool of mornings and late afternoon they are sluggish and easier to manually flick in to a soapy container to their death.

Insecticide Options for Control of adult Japanese beetles on leaves and flowers

Document by Dr. Whitney Cranshaw, Colorado State University

Sprays that are not effective for control of Japanese beetle damage to leaves and flowers. A partial list of products that have failed to control Japanese beetle in CSU trials would include the following active ingredients:

capsaicin canola oil

cottonseed oil garlic oil

horticultural oils (mineral oils) insecticidal soap

neem oil rosemary oil

spinosad thyme oil

Information from Dr. Whitney Cranshaw, Colorado State University