Brown patch can pop up quickly in hot, humid weather, especially with high nitrogen fertility and late afternoon and evening thunderstorms. Luckily, the very cool nights that have followed the brief hot spells will eliminate brown patch activity. Both fungi are in every soil will attack vulnerable, young turfgrass plants.
Pythium is most common when turf is too wet.
You can sometimes tell which fungus is active by the mycelium color, but Rhizoctonia can look quite white in wet conditions when it is growing quickly. Only a microscope can differentiate them for certain. Fungicides are not usually effective in saving infected seedlings. Overseeding is the best approach. Once turf has matured, it is not longer so susceptible.