Severely diseased plants should be discarded. If only a few plants are involved, remove all blighted leaves. Keep the foliage as dry as possible to reduce initiation of new spots. Water during the day to avoid leaf wetness at night.
Applications of Dithane M45 or iprodione will also reduce new infections.
To begin new plantings, purchase clean seeds. Dip seeds in a solution of 10% household bleach, e.g. 1 part Clorox and 9 parts water) with a few drops of detergent for 1 minute. Immediately plant seeds in clean potting mix such as Sunshine Blend 4. As seeds germinate check continuously for any signs of rot. If rots develop, discard all seeds in that pot.
If young plants are purchased at garden shops, check all plants for disease. If any plant has leaf spots, avoid all plants in that group.
Ideally, all old, diseased plants should be destroyed before new plants are started. Fields with diseased plants will harbor the pathogen for months and surviving plants produce spores that will blow over to clean plants. Alternaria survives in diseased plant tissue in the soil. Avoid reinfestation by growing the new crop in areas which have not been used for gomphrena for at least a year. Homeowners should consider planting gomphrena in large pots to allow time for Alternaria to die in contaminated gardens. Without such measures, this pathogen will persist season after season.