Question:
Japanese beetles are devouring my roses. What can I do?Answer:
Japanese beetles eat the foliage, fruits, and flowers of over 300 plants. When feeding on foliage, the beetles consume the tissue between the veins, leaving a lace-like skeleton. Flowers and fruits are sometimes devoured completely. Roses, raspberries, grapevines, crabapples, birches, and lindens are some of their favorite food hosts.
Adult beetles are present for about 6 weeks every summer. The adult beetles begin to emerge from the ground in late June and new adults continue to appear throughout July. Each beetle lives from 30 to 45 days.
Control of Japanese beetles is difficult. Persistence, diligence, and repeated efforts are necessary because new beetles emerge every day over a period of several weeks. Handpicking or screening of high-value plants may be of benefit in isolated situations with limited numbers of beetles. Remove beetles early and often to preserve the beauty of the plants and to reduce the attraction of more beetles. Remove beetles early in the morning while temperatures are cool and the beetles are sluggish. Collect or shake beetles into a bucket of soapy water and discard.
Spot spraying infested foliage of high value plants with a labeled garden insecticide may reduce damage for several days, but multiple applications are required to maintain control. Check the insecticide label to make certain the plant you want to spray is listed. Read and follow label directions.
Japanese beetle traps are widely available but have been shown to be ineffective in controlling moderate to heavy infestations. In fact, they may attract more beetles than they catch!
Learn more about growing roses in this article: Growing Roses in Iowa.