Grubs eating alfalfa roots

After baling second cutting in June I noticed some alfalfa crowns didn't regrow and died. I figured it was from drought as the whole field didn't regrow for two weeks after cutting until it rained. Now after third cutting which was baled about 10 days ago I have noticed many of the alfalfa crowns look very drought stressed and the regrowth is minimal. The thing is we have not been overly dry since cutting and many of the plants look healthy with 6-8 inches of regrowth.

I tried to pull up some of the poor looking alfalfa plant and to my surprise they came out of the ground very easy and the taproot was mostly all dead and looked like something had eaten much of it. I also found a couple plants that the taproot had a white grub eating the center out of the root. Anyone know what this pest might be and how to control it? I'm afraid the damage is already done and many parts of the field is going to be thin but I don't want this pest to continue feeding on the healthy crowns.



Grubs eating alfalfa roots