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May and June Beetles Flying (06/06/19)

Over the last two weeks, May and June beetles. Phyllophaga. spp., have been emerging and flying at night towards lights of houses, parking lots, etc..

Over the last two weeks, May and June bhort.1 3eetles. Phyllophaga. spp., have been emerging and flying at night towards lights of houses, parking lots, etc.. These beetles have a three-year life cycle ending with the emergence of adult beetles in late May or early June; hence the names May or June beetles. Adults are tan to brown, ranging from ½ to 1 inch long, with a smooth, hard exoskeleton. Adults mate shortly after emerging from the soil. Females lay eggs 3 to 7 inches below the soil surface. Eggs hatch in three to four weeks and produce white C-shaped larvae approximately 1 inch long when mature with six legs behind the head. After hatching, the larvae dig upward to feed on turfgrass roots for the rest of the summer. Feeding may cause the turfgrass to wilt, thin or even die in small to large patches. As fall approaches, the larvae migrate downward below the frost line to hibernate for the winter. They move upward again after spring arrives to resume feeding. The most extensive turfgrass damage is caused by the  second-year larvae. As fall approaches, the larvae move down below the frost line once again. They resume feeding for a short time during the third spring before pupation into the adult stage begins. Adults emerge from the soil the following spring to mate and complete their three-year lifecycle. Adults do not damage turfgrass; after emergence, they mate and feed on ornamental foliage for a short time, then die. Defoliation in the top part of ash, willow, cottonwood, oak, elm and other trees is easily visible now.

Signs of grub damage in lawns begin as small, irregular dead patches several inches wide. If control measures are not taken, the damaged areas can expand to several feet or yards in diameter. A simple way to diagnose grub damage is the “tug test.” Grasp a handful of damaged turf and pull; if the turf comes up in large pieces without resistance, the damage likely was caused by white grubs severing roots from the turf as they feed in the thatch layer or just below the soil surface. Diseased turf, although dead or damaged, will provide resistance during the “tug test” because the roots are still intact.

Skunks and moles often cause secondary damage to grub-infested turf by digging and tunneling for larvae just below the soil surface. Mole tunnels and skunk diggings may indicate a white grub problem.

In lawns, three to four larvae per square foot is considered an action threshold for insecticide treatment around homes. Systemic insecticides provide effective control if applied approximately one month before the heaviest feeding occurs. Contact or stomach insecticides can be used as a rescue treatment, but neither chemical control measure will revive dead or severely damaged turf.

An effective nonchemical control measure is to avoid thatch accumulation and maintain a vigorous lawn. Also, avoid permanent night-lights in or near the turf area. They attract adult beetles, which often lay eggs at night in turf adjacent to illuminated areas.

Biopesticides have not provided reliable control of white grubs. Beneficial parasitic nematodes are effective for white grub control only when soil moisture is adequate.

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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