Thank you for sending the image. It looks like rust, a fungal disease not on insect on the black mondo grass. This is caused by dampness and wet weather especially when plants are grown closed together and crowded. You could spray with a fungicide but in most cases this disease will clear up when the weather becomes drier. Try moving the potted plants under cover to keep the foliage drier and try not to wet the foliage when you water the pots and baskets. Good luck and Keep Growing, Marianne Binetti