The fertilizer did not cause the fungus. The fertilizer helps the pathogen in the soil thrive. Constant moisture (including humidity) promotes common summer lawn diseases including red thread, summer patch, brown patch and dollar spot.
You can manage these diseases with proper cultural practices in your lawn care program including proper watering and mowing.
You can help your situation by not watering your lawn in the evening as this helps to hold humidity at high levels next to your grass plants for an extended period of time.
Water deeply and infrequently; set your mower cutting height high. Apply Lawn Fungus Control at the higher (curative) rate to treat and it. Water in after application. Repeat in one month if needed. When mowing, mow the affected areas last and clean your mower blades (carefully) between mowings.