I've found that in a good brassica mix you'll have varities that mature at different rates and the deer will be specific on when they utilize each of them.
The deer begin eating my plots a fair amount come November. MK_M_GBL has had tremendous results in October with his brassica plots and has the photos of mature trophy class bucks gorging themselves on his plots. You just have to give your deer a season or two to know what exactly the food source is. As with any food plot, don't expect miracles.
