Thanks Rowan and Christopher

I’ve come to a similar conclusion. Recently I visited a farm down near Canberra. Going through a paddock, the farmer showed me how his perrenial grass plants were being wiped out by slaters. Same sort of problem. He has layer chickens out eating the slaters. This afternoon I was out in the same paddocks that were negatively affected with slaters in Autumn and found very high population still thriving, sucking the juice from top of lucerne (alfalfa) plants. In addition, they or the bigger white grub in pic are eating the phalaris plants off at the roots, just under ground. These phalaris plants powered through the cool season, growing well with roots to a meter deep. Looks like we’ll lose most of them.

I’ll do some trial plot plantings of summer crop and see if they get attacked.