The X-large population of fall armyworm (FAW) caterpillars generated by the X-Large population of FAW moths in late August (as indexed by UK-IPM trap counts, See: KPN 1245 Aug 31, 2010) should be past. This does NOT mean that the threat from FAW is over. It simply means that the large pulse of caterpillars generated by the extraordinary number of moths have completed the damaging stage of their life cycle. We do have evidence (especially forage fields having to be treated a second time) that this pulse did cause some producers x-tra trouble.
My best guess is that the FAW caterpillars produced from the X-large moth flight are now in the pupal (resting) stage, from which adult moths will emerge. So it is possible that another large flight could occur this fall, depending upon temperature. The only other recent, large, fall occurring, FAW population for which we have record, occurred on Oct. 5, 2007. This led to large numbers of FAW mostly feeding on volunteer corn (fortunately) in area wheat fields.
Regardless of whether or not we see another large surge of moths, FAW caterpillars will be present until at least the first killing frost and one should continue to monitor crops at risk. By now corn and most soybeans and sorghum are no longer in danger. Grass and alfalfa forages, especially newly established stands are at greatest risk. Additionally, any newly established grass stands including wheat, lawns and grass covers for construction and reclamation should be watched.