In September, annual white grubs can cause major injury to lawns. How do you know if you have them or have the damage? The first signs are an off color in large patches, kind of a dull green, usually in late August or early September. After a week to 10 days, the dull green turns to light brown, and then to tan.
In late September, the symptoms turn to signs with upturned grass and the presence of actual grubs under the sod, in the upper layer of soil. The good news is that they are easy to see; the bad news is that at this stage they are hard (but not impossible) to deal with.
The first step is to remove all of the upturned sod. It’s not going to regrow, so the best use of it is to put it on the compost pile along with the falling tree leaves. Next, choose whether reseeding or resodding is best. Either will work just fine, especially if it’s a smallish patch. Use a pitch fork to loosen the soil, then spread 2-3 pounds of Kentucky bluegrass (it’s too late to seed tall fescue) over the loosened soil or cut pieces of sod to match the damaged areas.
After regrassing, keep the new seed/sod moist, not soggy or dry. This is several-times-a-day activity the first 2 weeks, gradually backing off as the seed germinates and the roots of the sod take hold. Then, apply a light rate of starter fertilizer to enhance rooting. After the grass reaches 3 inches in height, begin mowing, but carefully as the new plants are not well established.
As the new grass is establishing, the grubs have probably moved on to adjacent parts of the lawn. To prevent them from damaging the previously unaffected areas, apply Sevin (carbaryl) or Dylox (triclorfon). Read and follow all label directions.