Lawn rust ?

Evening all, 

I think my lawn has rust ( I think this is a proper term, if not apologies).  I fed it in the autumn, spring along with moss control, raked out the moss and overseeded.  It looked great for a few weeks (although stripy due to not overlapping the feed), but I've now noticed it has rust coloured spots over the blades of grass and not looking great. 

Any advice as to what i do with it ?  It is super sandy soil, so today I put summer cut and feed lawn food on it, (probably more stripes now), but is there anything else I should be doing, will it kill off the lawn altogether or will it come back once we get more rain ? 

Any advice gratefully received.