Bill is 100% correct about the soil being imbalanced.
Without looking at the site, I would suggest top dressing with some high quality/locally produced compost. A soil test will tell you the OM% and roughly how much compost to spread. Apply 1/4" until you reach +/- 7%
Address compaction too.
All of that biology in the compost will be antagonistic to those grubs. They will find somewhere else to feed if conditions are tough enough for them.....think itching powder in the sleeping bag.....
As a rescue treatment (sounds like you need to do something NOW), you can apply two different strains of nematodes which can help a lot. This is not really a sustainable fix, but I have seen it work very well. We distribute them. Go to this link
for comprehensive info. Let me know if you need any other help.