Essentially, what you're dealing with when rust fungus invades is a case of plant parasitism that is detrimental to grass health -- small infestations might only cause a color change but larger ...

fungal diseases that infiltrate backyards across ... Other summer fungi of note include turf grass rust, which thrives in ...

All of these rusts release the bright rusty-orange spores once spring weather becomes mild and damp, often around late March to mid-April, so now is a prime time to look.