Insect Management

Japanese Beetle

SCARAB BEETLES IN VEGETABLE CROPS

    Japanese Beetles are active in early to mid July  in various crops and non-crop habitats.  Oriental Beetles are also active and, though less damaging, may show up in vegetable fields as well. Oriental beetles emerge a bit earlier and showed up in the last week of June, while Japanese beetles began emerging about July 4 (right ‘on schedule’ relative to past years). Both species are starting to lay eggs now.  Possibly because of the mild winter, numbers of both beetles are high this year.

    There are four species of scarab beetles that are common in New England turf, fruit and vegetable crops. These were all introduced to the US. Japanese beetles are the most common and widely distributed scarab species in New England and until about 10 years, they were the primary grub species in most of New England.  Oriental and Asiatic Garden beetles are relatively new “imports” and their range is expanding.  Below are brief descriptions.

    Japanese Beetle adults are about half an inch long, with a metallic green head.  The wings are shiny copper or bronze color, and there are a few tufts of white “fur” along the side of each wing when it is folded back over the body.  The adults are active in daylight and feed on many different kinds of trees, fruit and flower crops. In vegetables, adults can cause silk clipping in corn, and leaf damage in sweet basil, collards, other greens, green beans, eggplant, asparagus, rhubarb, and peppers.

    Oriental Beetles fly at night, but are very active during the day as well. The beetles are just a little smaller than Japanese beetles, and usually are a rather mottled gray with black splotches. The pattern and color varies. Occasionally an individual will be almost all black or almost all gray. The antennae are branched and are quite striking if you take a close look. There are more beetles flying this year than usual, which will probably translate into a more significant year for grub activity in turf.  Grubs are not known to be active in vegetable fields and crops, though this is not well studied.  Adults feed less on foliage than Japanese beetles so are not generally a concern in crops. 

    Asiatic Garden Beetles are about half as long as a Japanese beetle adult, and somewhat more “plump” in appearance.  They are reddish-brown or copper-colored.  They often are found near roots of plants when one is weeding. Adults tend to cause more damage to vegetable crops than Oriental Beetle, but less than Japanese beetles. Their numbers don’t seem to be especially high this year. Larvae feed on beet, carrot, corn, lettuce, onion, Swiss chard and strawberry.  Adults feed on carrot, beet, parsnip, pepper and turnip.

    A fourth species may also be found: European Chafers, which are slightly larger than Japanese beetles and are a fairly dull brown or tan in color.  They are night fliers but can be seen in large numbers just at sunset, when they congregate in large numbers in favorite trees (such as locust or willow). Adults are not foliage feeders and grubs are mostly a turf problem. Feed through October or November.

Life Cycle

    The life cycle of the Japanese beetle fits most of the species of grubs we encounter in New England, with minor variations depending on the species and the location.  They have a one-year life cycle, with adults emerging from the soil in early July in most of Massachusetts (later farther north) to feed and mate.  The females burrow into the soil (often in or near wide expanses of sod or turf grass) to lay eggs, usually beginning in late July.  Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads).  The first grubs usually appear around late July or early August and begin feeding on roots of grasses and other plants (including corn).  After about two weeks of feeding, the grubs molt to a second “instar”, and feed for another three weeks.  The grubs molt once more, to the “third instar” (or large grub) around the middle of September, and continue feeding until the soils begin to cool down. In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter.  In the spring as the soils warm up, the grubs move back into the root zone and resume feeding for about six weeks.  By the middle of June, most grubs have completed their feeding requirements and pupate (still in the soil) for about a week before emerging as new young adults.

Contols

    On turf, insecticide controls normally target young grubs just as they begin to emerge from eggs. In vegetables, managing the grub stage may not be feasible (or necessary) since the grubs are most likely feeding elsewhere.  However, vegetable growers could run into problems with grub damage if turf or sod is plowed under in fall or spring and followed by a spring vegetable crop. Insecticides may be needed to control adult beetles if numbers are high and damage is significant. The 2006-2007 New England Vegetable Management Guide lists products for Japanese and/or Oriental Beetles in basil and sweet corn. For controls in a crop where these beetles are rarely a pest and therefore not mentioned in the Guide, check the label of commonly used broad spectrum synthetic pyrethroids, carbamates, or pyrethrin.

--Update from Pat Vittum, Turf Entomologist, and Ruth Hazzard

Updated July 2006

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