By: Louise Coleman, roseylou[at]aol[dot]com
Japanese Beetle Scientific name: Popillia japonica
The Japanese Beetle was first discovered in a nursery in New Jersey in 1916. It probably came from Japan in a soil ball around imported plants. By the following year it had infested a three mile area and within two years covered over 50 square miles. Each year there is a natural outward movement of the beetles and they now cover all of the North East, parts of the South and Mid-West. They have now spread west as far as Michigan and Missouri. The amount of summer rainfall is the main climatic influence on year to year changes in the number of beetles. Rainfall in June, July and August in most of the East is normally about 12 inches. When it is below 8 inches there is a high mortality of eggs and beetles are less abundant the following year. In areas of the West the summer rainfall is probably too low for survival. However, in 1961 Japanese Beetles were found in Sacramento, CA, but eradication measures were immediately taken and proved successful.
The beetles are attracted to over 300 plants, mostly ornamentals and especially roses. Being gregarious, they are often seen in large groups, devouring a rose bloom. Adult beetles feed from late June to early October with a peak infestation during July. They always appear in my garden in New York on Fourth of July weekend.
The life cycle of the Japanese Beetle is two years. The female lives about 45 days and in the late summer lays 40-60 eggs, usually under grass roots in lawns. The grubs hatch in 10-12 days, feed on grass roots until cold weather then move down in the soil to avoid being frozen. In the spring, they move up in the soil, again feeding on grass roots until pupation in the soil in late May. The 3/4 to 1 inch grubs are grayish white with brown heads and are usually found in a curved position.
Control of Larvae:
Lawns may be grub-proofed with Diazinon® granules or other grub products sold for lawns. The turf may be treated in spring or fall. Care must be taken in areas that are frequented by children, pets or wildlife. In this case, the chemical should be well watered into the soil so no residue is left on the surface.
Control of the Adult Beetle:
Nature places many controls on this beetle. Bird predators include Starlings, Grackles, Cardinals and Meadowlarks. There are also five parasitic wasps that can infect the beetle. Two of the most effective are tiphia vernalis and tiphia popilliavora. Colonies were released in nine eastern states in the early 60s. Milky Spore Disease, which is harmless to humans and animals, attacks the grubs and in time can provide adequate control. Sevin® has proven effective in killing the adult beetle when used as a spray or dust.
However, Sevin is a broad-spectrum insecticide that will also kill beneficial insects that keep mites under control so be sure to keep an eye out and take measures to control a mite infection if you use Sevin. Weekly treatment is necessary to protect rose foliage but nothing will keep Japanese Beetles from feeding on the flowers that open between spray applications.
Rotenone or pyrethrum sprays and dust will kill the adult beetles that are thoroughly covered during application but will not repel a new group of beetles. Neem oil products claim to repel the beetles and must be sprayed on a 5-7 day schedule to work successfully. Beetle traps seem to attract more beetles than they catch and should only be used far away from the rose garden. (A neighbor’s house across the street would be a good location.) When all else fails, hand picking several times a day can reduce the number of beetles that can destroy the roses today and lay eggs for another generation tomorrow….
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