Finding white grubs this time of year is pretty common

September 28, 2018

White grubs are being found in lawns, vegetable gardens and even crawling across streets in Grand Island. I have not had reports of grubs in the streets and I don’t expect to, but it is possible.

While finding large, white, c-shaped grubs create concern, this is normal at this time of year. In most cases, grubs have done the damage they are going to do for this year and insecticide control late in the season is not very effective.

Grubs damage lawns by feeding on grass roots. If grub numbers are high, enough roots may be damaged to cause turf areas to turn brown. Kentucky bluegrass is much more likely to show damage due to its shallow roots. Tall fescue has few problems with white grubs and treatment is rarely needed on fescue.

In vegetable gardens, damage is most common on potatoes. But grubs are rarely a serious enough issue in home vegetable gardens to warrant control.

If control is needed on Kentucky bluegrass (KBG), aim control at the next generation next season. If eight or more grubs are found in a KBG lawn at this time of year, an application of a preventive insecticide may be warranted next June. The use of preventives is only recommended on lawns that had damage the previous season.

It is common to think that if grubs seen now are killed, then grubs will not return next season. However, the adult beetles fly and new ones fly in to lay eggs.

And there are natural enemies or environmental conditions that can reduce populations between now and next summer. Having large grub numbers now does not mean there will be even more next season.

The worst damage that could occur at this time of year is from skunks and raccoons. Skunks scratch and tear up grass to reach grubs. Raccoons turn the sod over to expose grubs to eat.

When grub control is needed in late August or early September, the insecticides Dylox or carbaryl are recommended. Both products are more effective against younger grubs if applied in late August or early September.

Insecticides are less effective on full-grown grubs so trying to control them now usually does not stop skunks or raccoons from damaging lawns. Tidy up any turf that is torn up or turned over and water to help the area recover.

White grubs are the larvae of a group of beetles known as scarab beetles. Larvae of most scarab beetles are not damaging pests. There are four beetles in Nebraska whose larvae can damage turf if grubs are present in high enough numbers.

Our most common scarab beetle that is a lawn pest is the masked chafer. Less common beetles in our area are May/June beetles, Japanese beetles and the black turfgrass ataenius. All grub types are controlled at the same time of year and with the same products, so it is not important to determine which one you have.

Another scarab beetle seen less often is the green June beetle. It is the larvae of this beetle that has been found in the streets of Grand Island. Green June beetle grubs are unusual in they will emerge from soil at night and crawl on the surface on their backs.

It is unusual to see them crawling across streets. All of the rain and wet soils this year may have chased these grubs into the street in search of a well-drained soil. While I have had green June bugs brought in for identification this year, I’ve had no reports of grubs on streets.

Don’t be too concerned about white grubs found in soil now. If you had eight grubs per square foot in a KBG lawn, mark your calendar to apply a preventive next June or early July.

Kelly Feehan his a community environment educator for Nebraska Extension

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