Fescue, like other turf grasses, is susceptible to a variety of fungal infections. Fungus is most likely to attack a fescue lawn that is improperly maintained and is a sign that your lawn needs better care. Fungal fescue diseases can be treated with fungicide, but these treatments can be quite expensive. and will likely have to be applied season after season. Proper lawn maintenance is the only long-term cure.
Look for sunken, circular patches of matted dead grass (which may be orange or dark gray) with white fungal growths at their edges. These patches are suffering from pythium blight. This fungus usually crops up in late spring in lawns that suffer from too much heat and water and especially lawns that have recently been seeded with too much seed. Heavy fertilization in late spring can also encourage fungal growth by providing it with lots of tender new grass shoots to feed on.
Scan for small, dead patches that appear shortly after a heavy dose of fertilizer in summer. These small spots are caused by "brown-patch" fungus. And as the fungus spreads, these patches will grow and join together in clumps that can reach more than 3 feet across.
Allow fescue that is susceptible to brown patch to go dormant in the summer. This means that it should not be fertilized at all during those months and only watered once weekly (early in the morning to allow the grass a chance to dry out before nightfall).
Look for large oily or slimy patches in your fescue lawn. These patches are caused by slime mold fungus. These slimy patches will eventually turn gray and then black. While unsightly, this fungus does not actually feed on the grass itself and it can be washed off with the hose.
Search for small dead patches of grass that are roughly 6 inches in diameter. These small dead patches are caused by dollar spot fungus. This fungus most commonly attacks fescue lawns that are suffering from drought or lack of fertilizer.