The Japanese beetle, according to Vera Kirchik, (JB) is a serious pest of turf and ornamental plants. Grubs feed on the roots of grass and adults feed on the foliage of more than 300 plant species.
Japanese beetles were first found in United States in 1916, after being accidentally introduced into New Jersey. Until that time, this insect was known to occur only in Japan where it is not a major pest. It is controlled in the eastern United States by soil-inhabiting protozoans that are not present in Minnesota. There are two biological control agents, the fly Istocheta aldrichi and the tiphid wasp, Tiphia vernalis, but they do not control infestations.
Japanese beetle adults are approximately three-eighths inches in length with a dark metallic green head and metallic dark tan wings. Key characteristics for adult JB are two white rear tufts and five white lateral tufts of hair. Japanese beetle larvae or grubs are "C" shaped and live in the soil and feed on grass roots. JB was recorded to feed on the roots of corn, beans, tomatoes, and strawberries.
Grubs chew off grass roots and reduce the ability of grass to take up enough water to withstand stresses of hot, dry weather. As a result, large dead patches of grass develop in grub infested areas. These dead patches can be rolled back like a carpet to expose the lack of turf roots. Grubs can be found in adjacent green areas. Early recognition of the problem can prevent this destruction. Starlings and crows, as well as moles, shrews, and skunks may be seen digging up grubs, also damaging the turf.
Adults emerge from the soil in early July, feed, mate, and lay eggs. In July adults are noticed feeding on vines, linden trees, roses, and many other ornamentals. Activity is most intense over a 6 to 8 week period, after which the beetles gradually die off. Individual beetles live about 60 days. Over 2 months females can lay a total of 60 eggs.
JB adults feed in full sun at the top of plants, moving downward as the leaves are consumed. Odors emitted from beetle-damaged leaves causes beetles to aggregate. Also, adults release an attraction pheromone that causes them to aggregate. At dusk, this pheromone is no longer produced and the females fly to turf to lay eggs. Females burrow 2 to 3 inches into the soil and lay their eggs. The grubs grow quickly and by late September are almost full-sized (about 1 inch long). When the soil cools to about 60 degrees in the fall, the grubs begin to move deeper. Most pass the winter 2 to 6 inches below the surface, although some may go as deep as 8 to 10 inches. Grubs feed again in May when ground temperatures are above 50 degrees.
Adults fly long distances to food plants; so adult infestations do not indicate turf infestations. The best time to apply insecticides for grubs is from mid-July until early September. Granular applied insecticides distributed on soil with a spreader are usually the best insecticides for JB.
Before applying an insecticide for grubs, make sure you have a large infestation. The best time to apply insecticides for grubs is from mid-July until end of September. Granular applied insecticides distributed on soil with a spreader are usually the best insecticides for JB.
There are conventional insecticides that kill grubs (imidacloprid) and biorational insecticides that conserve beneficial insects in turf (halofenozide and Acelepryn). In trials in Ohio milky spore disease (Bacillus popillae) has not been as successful in killing JB grubs as was reported in the 1960s. A beneficial nematode, Heterorhabditis bacteriophora, attacks JB grubs. Nematodes are microscopic parasitic roundworms that transport and feed on bacteria. When they find a grub, the nematodes penetrate the larva and inoculate it with bacteria, which quickly multiply within the grub's body. The nematode then feeds on the bacteria. Nematodes need to be applied to soil at night and the soil must be irrigated daily to kept it moist so the nematodes stay alive.
Removing beetles by hand may provide adequate protection for backyards, especially when beetle numbers are low. The presence of beetles on a plant attracts more beetles. The plants that attract JB are American chestnut, American elm, American linden, American mountain ash, apple, birch, black cherry, cherry flowering crabapple, grapes, hollyhock, horse chestnut, Norway maple, plum, roses and walnut trees.
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