I am sorry for this delayed reply to your gardening question. The spring rush has brought a deluge of questions and we are working hard to catch up!
That is very strange about your fountain grass. I cannot think of anything that would do that unless the affected grass is in less sun or in a poor soil condition. Dry soil, tight clay soil, or any such factor could be the problem. You indicated that they get the same sun and water, so there must be something in that spot. Try digging the plant up reworking the soil and adding an inch or two of compost and then resetting the old plant or a new one.
Thanks for the question. Best wishes for a wonderful gardening season. Please stop in again soon!
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