Rusty Spots on a Lawn

These "rust" spots are Not the normal Rust that can occur on lawns. That fungus disease is usually seen later in the season. And if it was the Rust disease, the rusty or orange colour would come off onto your shoes as you walk through the lawn.

What it looks like to me is that this lawn- at some point in the past had some spots of another disease called Necrotic Ring spot. This can leave circles and donut shaped areas where the grass dies out.

When the lawn is seeded to fill in those spots, often fescue type grasses seem to be better able to grow. This makes sense as the Kentucky bluegrass of the rest of the lawn is generally more susceptible to Necrotic ring spot.

Fescues while generally more drought tolerant than other lawn grasses, can turn a rusty colour when there is inadequate moisture. I think the earlier May drought has caused this off colour.

Recommendations-
The colour should recover with the recent wet weather. The lawn looks like it could use some nutrition. Make sure however to use a very slow release fertilizer.
The lawn would do better if mown at a mowing height of 3" high.
The necrotic ring spot symptoms can re-occur- if that happens, seeding is recommended.