Late-season N: Recent research on bermudagrass found that late-season N applications prior to frost promote fall color retention and do not have a negative effect on bermudagrass winter hardiness. Late-season fertilization is highly recommended for athletic fields and some newly established lawns. The only downside to this practice is that it will increase winter annual weed pressure and may predispose bermudagrass to more injury from spring dead spot and zoysiagrass and bermudagrass to more large patch. ... I know the OP addressed Northern climate, but someone tried to make the issue obligatory to Southern grasses somewhere. Another thing we did in TX was overseeding with annual/winter rye. Except St Aug.