My mature ground cover has developed rust colored leaves and flowers here and there in patches. It seems to be spreading. The plants otherwise look very healthy and the flowers appear to be perfect until they turn the same rust color as the leaves.
This early spring when the winter dieback was clipped off it was not removed from the plants. The landscaper thought it would act as a mulch; it seemed like a good idea at the time. I am wondering if that is the cause of the problem as I usually rake the clippings away from the plants and have never had this problem in the past. Would love to stop the problem before all of the plants die. Any suggestions?
Based on your description this sounds like a rust disease. All you can do is remove infected plant material at the beginning of the season and any plant material that is dead and dispose of. Do not let it lay in the beds. You will have to monitor and decide if you want to spray a fungicide next season. This will not cure any infected plant material already there. Fungicides are preventatives. You have to spray as soon as you notice symptoms. This protects new foliage.