If you have more than 12 of these bad boys in 1 square foot of grass, then they are the culprit. Normally lawns can tolerate some grub feeding without showing damage, but when you get above the critical number of about a dozen, then you are going to see the damage.

Good and bad news is the damage is done. They are finished feeding for the season. If you kill them now you are closing the barn door after the horses are gone. The time to stop them was last July (possibly even before you became aware of the damage). If you spend the money to kill them now, it will just be spiteful...which is not a bad reason now that I think about it. Do you remember last June whether your porch lights were covered with beetles? That is one indicator that you are about to have a grub problem.

If it happened like that to me, I would spend my money on making the lawn look better rather than killing the sleeping grubs.

This is for you and you along in the California high desert: I believe the very best thing you can do now is to winterize. Without grubs I would suggest winterizing later in the year, but you have this going on. You are between the Labor Day and Thanksgiving holidays when lawn fertilizer seems to work. Since it is this long after Labor Day, I would go ahead and winterize. Winterizer fertilizer is high nitrogen/fast release chemical fertilizer. It causes fast growth at the tops which feeds the roots. One thing you could do at the same time as winterize is to apply an organic fertilizer like alfalfa pellets. Apply at 20 pounds per 1,000 square feet. That will do more for your soil (and lawn) than any combination of other treatments you might consider - especially if you have not used an organic fertilizer in a long time.

Is your soil made of the loose rubble that is common in the high desert or did they bring in fill that looks like soil?

Have you ever had your soil tested by a professional (not university) soil test lab? My worry in the SoCal high desert is boron levels. The only place to get a good soil test I know of is Logan Labs. Their $20 test is better than most university special order tests costing $100 or more. It will give you boron levels.

Boron is a tricky element. All life needs a little bit, but once you get more than a threshold level, nothing lives.

d_schall - so you are saying I wasted my money in applying anti-grub "fertilzer" 3 weeks ago here in NW Wisc.?

What was the active insecticide ingredient in the fertilizer?

Yes 1111, that's what I'm saying.

just f'in great!