[Gtgoose]

So i have a fairly new lawn (September 2017), South facing in Denver, CO. I gave it a winterizer, then 2 spring fertilizer feedings of Richlawn fertilizer about a month apart. I've been watering by hand and everything was greening up really nice, been mowing it, etc. but then it just started yellowing up on me as you can see in the pictures.
Underwatered? Over watered? Fungus? Too much nutrients? Not enough?
Any advice is appreciated.
Thank you

 

[g-man]

Did it start small and grew in size or was it sudden?

How much fertilizer did you apply and how big is your grass area?

 

[Gtgoose]

It was sudden.
Total grass area is about 200 sq ft. (10x20). The dead spot is about 3'x4'.
One pass with the spreader at 70% open each time. Richlawn says 60% open every 4 to 6 weeks.