If you've experienced losing areas of lawn to grubs before, you may feel dubious putting new grass down---and with good reason! But populations of grubs fluctuate from year to year. Laying down sod at the right time and using insecticides when and where they're necessary can help you save your lawn from damage so bad that you need to replace it again.
Planting New Sod
Before laying sod for the first time, take stock of the surroundings. Are there fields nearby where the Japanese beetles or June bugs (the adult form of the common white grub) might be spending their summer? Have neighbors complained of grubs? Check the yard for existing grubs by spading out a section of dirt 3 inches deep in potential problem spots. If you don't see any, and assuming you are not replacing sod damaged by grubs, the coast should be clear to lay sod.
Plugging to Replace Lost Sod
If you are replacing sod in areas where grubs have attacked and killed the grass, make sure you don't do so while they're still active. Sod has very little in the way of roots to begin with, and an active grub infestation will just gobble them up before they're established. Likewise, grass plugs need time to adjust to their new home before they're ready to replace roots lost to grubs. Control the infestation first, then plant new sod when your local extension service says that grubs aren't currently active.
If your area is prone to grubs, you might consider using biologically helpful nematodes. These microscopic insects infest grubs, making them too sick to eat and eventually killing them. Nematodes can usually be purchased through the extension service or from online companies. Using nematodes instead of chemical insecticides prevents killing beneficial insects and keeps grub populations under control.
When to Use Nematodes
Apply nematodes in the cool of the morning, preferably on a cloudy day. Wait until it's the time of year for the adult beetles to lay their eggs, so that there's something for the nematodes to eat. Water them into the soil as you go. You can apply them as you lay sod so that they're protected under the grass mats. If there are already grubs present, the nematodes will get to work immediately. If not, they can survive in the soil for a few days while they seek or wait for their prey.
There are a number of grub treatments for the lawn once grubs are present. Most are granular and must be watered deep to kill existing grubs. If you've just laid your sod, you can pull up corners here and there to check for grubs up to 3 inches in the soil before applying insecticide. Do a broad sweep of the yard when you're checking for them. While there may be many grubs in one area, another may have none. Remember that applying chemical insecticide to your lawn will kill insects that hunt grubs along with the grubs themselves, and grubs build their populations back up faster.