Fall is the best time for aerating and seeding your fescue. Fall gives you your best chance for proper establishment of the root systems before we hit the summer heat. Fall weather can also be a challenge to the young seedlings. During periods of heavy rainfall during the seeding season from September to November fungal diseases can be a problem. The photo to the right shows not only rhizoctionia (brown patch) activity ( the circles) but also pythium seedling disease, called melting out, ( the general thinning of turf).
In some cases if you look closely at the base of the turf blades in the thatch layer you can see the actual mycelium from the pythium fungus as in the photo below.
In some cases applications of fungicide can help control the problem but these are costly. If this fungal activity is active then the best course of action is to treat with a fungicide for the pythium and a fungicide for rhizoctonia to control the fungal outbreak then reseed to replenish the stand. It is usually not economically feasible or environmentally sound to try to treat these problems preventively as these problems are more the rarity than the norm most years.