Oats are very prone to residual herbicide damage. Heavy applications of some herbicides, particularly in heavy soils, will kill oats for several years after application. Damage is about as you describe.
+1
i refuse to use herbicide on food plots. This year we will plant oats and wheat on about 15 acres of food plots on three widely dispersed places. We plant our oats after the grass has turned brown and after a decent rain. i like the ground to have a lot of moisture when we plant. The old Okies call it "mudding in oats".