These things are terrible in my part of southeast Pennsylvania. Every year there are people in my neighborhood that lose significant patches of lawn to these things. I have skunks continually digging small holes in my lawn to get at the grubs. I know they are sod webworms because I have seen the moths flying, and have capture them to identify them. Also I have dug up the grub/worm stage in my shrub beds.
To top it off, we have Japanese beetles very bad here, and the white grubs associated with them are horrible. So we have two nasties: sod webworms and Japanese beetle grubs.
I have found that Bug-B-Gone Max seems much more effective than Grub-Ex. In fact, it seems like Grub-Ex is totally ineffective. This is measured by an informal count of the number of holes I see in my lawn from skunks. The BBGM seems to be followed by a reduction in skunk damage.
My lawn treatment program consists of monthly applications of Bug-B-Gone Max, and heavy monthly overseeding. If I didn't do this, my front lawn would be almost eliminated. There are portions of my lawn that have little grub activity, and these look like lush dense green carpets from the high maintenance. However, the heavily affected areas don't look so great.
Anyone else have problems with these things?