Dying individual or scattered stems in a mass planting or perennial clump can wilt or be killed for a variety of reasons that are sometimes hard to diagnose. Stem-boring insect larvae, breakage due to wildlife, and certain infections (Southern Blight being one of several) can all result in stem collapse and leaf browning. Since a fungicide will not be effective for situations where a fungal or bacterial disease caused wilting and dieback, since such products cannot cure existing disease, all that can be done is to prune out the stems in decline, since once wilted, they rarely recover (if insufficient water is the culprit, usually more of the plant will be equally affected).

The leaf speckling (stippling) visible as one of the symptoms was probably caused by a sap-sucking pest like thrips or (more likely, given the size of the stippling) leafhoppers. Given the mainly cosmetic damage caused by stippling, no intervention is needed for this symptom, especially since use of an insecticide would put the plant's pollinator/ecological value in jeopardy.

For now, just trim back any areas of dieback (especially if it helps to thin-out a crowded clump), keep monitoring the plant for watering needs given our current drought, and feel free to share any new symptoms with us for assessment.

Miri