Before assigning blame to grubs, can you answer a couple questions.

How have you been watering over the summer (duration and frequency)?

Does water accumulate in the area where the dead grass is?

Sometimes you can have multiple things going on, and the easiest thing to blame is the giant ugly grubs.

Grubs feed less and less as the summer goes on. Also there should be some tolerance in your lawn for a certain amount of grubs. If you have more than a dozen grubs per square foot of grass, then you have a problem. Fewer than that and grubs was likely not your problem. In any case now is the time to get your lawn fixed. I would give the Bayer time to work. Applying anything now is like locking the gate after the horses are out. Any grubs you have are not going to wipe out any more lawn.

Reseed NOW. Rake up the dead stuff, scatter seed, and step on all the seed to push it into the soil. Then start watering 3x per day (breakfast, lunch, and dinner). When you have 80% germination, start to back off on watering frequency. Mow when the new grass is 5 inches high. Mow it back to 4 inches. If you really want it lower then you can go as low as 3 inches (mid setting on your mower). Happy grass (and happy people) is somewhere between 3 and 4 inches.

According to one of our local nurserymen, grubs rarely strike the same lawn two years in a row. I've never had them once and getting data like that is hard to do on these forums. Grubs come from the beetles which swarm your porch lights in the late spring. If you don't get the beetles, then you probably won't have grubs and will not have to use any more insecticide.

Insecticide is really hard on your soil. One of the classes of beneficial microbes in your soil is called microarthropods. Those are insects too small to see. The insecticide kills out those little guys. And when you lose an entire class of microbes, it affects the entire ecosystem in your property. It would be like wiping out all fish from the Earth. Everything is affected.

No watering over the summer. Water does not accumulate, it's sandy soil.

Yes, more than 12 grubs per sq ft in some areas.

I am planning to reseed, but wanted to kill the grubs first.
Are you saying it's not necessary?

Thanks.

Grubs are your problem. now is the time of the year grubs do the worst damage. spring grubs are seldom a problem, this is why lawn service companies push grub treatment in the fall. I have seen turf pull up like loose carpet in the fall because of grubs. They are feeding on the roots so they can survive the winter and become beetles next summer (most likely Japanese Beetles). If you kill the grubs now your grass will recover. I have seen this numerous times. Lay the grub killer down (granuler) and water water water. You may see fungas but don't worry keep watering. If your grass dries out it will die. If you don't kill the grubs they will return in the spring for a brief feeding before they turn into beetles. also a starter fert will help put this down when your grass starts to recover not before. For sure if you are seeing that many grubs per sq ft. that IS your problem.

This post was edited by ed1315 on Sun, Sep 8, 13 at 21:46

this illustration clearly shows the Japanese beetle life cycle. Note the most active feeding stage of the grub is in September, October and November.