You might have had a faster response on the Ornamental Grass Forum rather than this image posting site ...
Hopefully you haven't removed the grass! There is nothing really wrong with the grass. It has 'foliar rust' - this is a fungal disease that is more common when the plant is stressed &/or when the weather is warm & humid with little air circulation. Can be chemically controlled with a fungicide.
or
Improve air circulation, clean up all foliage at the end of the season, provide plant with lots of tender loving care :o)
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