Answer: It sounds to me as though your plant has developed a rust disease. Rust diseases are caused by various fungi and produce pale yellow to rust colored areas on upper leaf surfaces and powdery spots of fruiting bodies on undersides directly beneath. Infected balloon flower stems and flowers may be seriously deformed. Remove any infected leaves as soon as possible. Rust can be prevented by periodic sprays of wettable sulfur on vulnerable plants, starting several weeks before the disease normally appears. Space plants widely apart for good ventilation, and avoid wetting the foliage when watering.
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