Diagnosing lawn problems can be tricky from symptoms that often overlap between one cause and another. It does look like rust in the photos despite the blur. It is not typically that bad of a problem because with any fungal infection, as the environmental conditions change the fungus will die off or go dormant until conditions are favorable for it again. 

Shorter lawn blades will stress the grass in other ways, plus the fungal spores spread so easily in the wind, from shoes, and favorable weather conditions, so mowing at the highest setting or between 3-4 inches is recommended. Also why sanitizing the blades between mowing areas is impractical and not necessary. You could try to bag the clippings when you mow and then discard instead of compost but again, this is a common infection in favorable weather conditions and 

The nitrogen can help and needs to be applied at a rate that complies with Maryland fertilizer laws. If you already fertilized this spring a second lighter application can be made as long as it fits with in the limits for the year. You can review our page on Fertilizing the Home Lawn and that should help clarify. A half rate of what is recommended typically and that should be fine. Let us know if you have questions with it or anything else.

Emily

It can be helpful but isn't necessary. Potentially one application a year is all that is needed and there are organic options over manufactured chemicals. Aerating and overseeding once a year in the fall is the best way to maintain an organic lawn without using chemicals. 

You can visit our Organic Lawn Care page for further guidance and feel free to ask us more questions. 

Emily

you're welcome!