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White Bugs & Circular Patches of Dead Grass

Typically, your lawn looks great in the rainy months of spring and early summer, while the grass is growing strong and the roots are developing well. But the damage caused by grubs, those white bugs under the grass, may often appear later in the summer and fall when the grass is dryer, stressed and no longer growing for the season. Test sick patches by tugging on the grass. If it comes up easily, white grubs are possibly eating the roots.
  1. White Grubs

    • Chafer beetles are one of the culprits in lawn circles.

      There are eight kinds of beetle larvae, also called grubs, that commonly cause damage to lawns by eating the roots of the turfgrass. All the larvae are similar in appearance, fat white grubs that normally are found curled in a "C" shape. June beetles, Japanese beetles, black turfgrass ataenius, Oriental beetles, European chafer, Asiatic garden beetle, green June beetles and masked chafer are all species found as garden pests as adults and as larvae in lawns eating the roots.

    Diagnosis of Grub Damage

    • Skunks will dig holes in the lawn and peel back turf looking for grubs to eat.

      Circular or irregular patches of dead or yellowing grass may be a sign of grub infestation. To check, grasp the grass firmly and pull upward. If the grass will not come up then it may be damage from dog or cat waste, drought or other causes. If the grass comes out, there have probably been grubs eating the roots and loosening it. You may be able to see them in the soil below. Damage to the lawn from skunks or raccoons digging is also a sign of grubs, as they are eaten by those animals.

    Prevention of Grub Damage

    • The easiest and best way to control grub damage is to water your lawn as the summer gets drier. A healthy, unstressed patch of turf will bounce back from grubs feeding on the roots and outgrow the damage. Control grubs and adult beetles with insecticides in July. When applied earlier in the year, it will not be as effective. Organic controls of the grubs are parasitic wasps, nematodes and fungal infections. Organic controls are of limited use.

    Repair of Grub Damage

    • To repair sections of turf killed by grubs or by animals hunting them, rake away the dead grass and debris and water the area. If the area is large or thinly grassy, reseed and continue to irrigate as needed until fall dormancy.