Costal Bermuda Hay field heavily damaged by Billbugs

I have had an irrigated, fertilized and babied , field 40 percent destroyed by Billbugs since the last cutting. I noticed several large areas that did not green up after the last cutting, and blamed it on everything , poor fert spread pattern, hot and dry, yes pivot irrigated but everyday for 60-70 days has been 98 +, with less than an inch of rain, herbicide left over in sprayer, cutting too low last time etc. 10 days ago noticed the dead areas were spreading. So used a weed eater to cut back a 2 x2 area, then poured a bucket of soapy water on the cut area, and the ground soon erupted in these little black beetles identified as Billbugs.
My UGA forage team says never seen in hay field before , but they regularly damage lawns, golf courses and commercial turf fields. I am at a loss , no pun, to why and how this happened. Anybody else ever experienced this?? Btw, 3 army worm apps have been made this summer.

Costal Bermuda Hay field heavily damaged by Billbugs