Are there a lot of weeds in your plot or is it healthy? I planted a white clover plot last year that got choked out by weeds and was untouched. This year, I put some Arrest on it and they have mowed it off all year, even dug holes in 10" of snow to get at it. Are there a lot of other food sources in the vicinity (standing corn, etc.)? Is it in an area where they feel safe eating it?