June beetle numbers high in 2011

With the large flight of adult June beetles this year, watch for a high white grub population and increased root injury the next two growing seasons.

The 2011 flight of adult June beetles is possibly the biggest I have seen in my 21 years in the Grand Traverse Bay area. These relatively large, brown to blackish beetles are fairly common every year. We notice them as they bounce off our windows at night as they fly toward sources of light.

There are about a dozen closely related species of June beetles (also called May beetles) that are very difficult to tell apart. They live for one to three years as a grub in the soil, feeding on plant roots. The grubs are soft-bodied and mostly white with six legs and a prominent brown head. When disturbed, they curl into a “C” shape. When full grown, they pupate and transform into adult beetles which leave the ground in the spring. The grubs can be serious pests of lawn grasses, ornamental plants and agricultural crops. The adults feed very little, typically causing inconsequential injury to plants. The high population of adults this year has resulted in some noticeable feeding injury to the foliage of tender-leaved plants, especially if they are located near the lights attracting the adults.

The great number of adults may result in a significantly larger than normal deposition of eggs in the soil over the next few weeks. If conditions favor egg survival, there will be a large number of tiny grubs by early July, ready to eat the roots of plants and potentially harm lawns, landscapes and crops. Most of the harm will not come this year, but as we get into the 2012 growing season, the damage potential will increase as this generation of grubs – now larger – begins a second year of root feeding. The adults of the eggs being laid right now will not appear until the spring of 2013 (for pictures and more information, see Dave Smitley’s article, Large flight of June beetles could mean more grubs next year).

Be watchful for high white grub populations and increased root injury for the next two growing seasons. It will be important to watch out for grub injury in turf grasses, small grains, hay fields and on woody plants recently planted into sites that had grass cover crops. If you need information on grub identification and control options, feel free to contact your local MSU Extension office.

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