Leaf spots are light tan to brown and usually have a concentric ring or target pattern with a yellow halo. As leaf spotting increases, blighting and defoliation soon follow. A. panax can survive the winter on infected crop debris. The following spring, the fungus produces spores which are spread to new growth by wind, rain, and splashing water. Disease development is favored by warm, wet, and humid weather.
Fungal spores germinate and infect the plant when stems and leaves are wet.
To prevent Alternaria leaf blight, avoid planting ginseng in areas with poor air circulation and avoid close plant spacing. Keep foliage as dry as possible. Once the disease is identified, collect and destroy all foliage with disease symptoms. If more than a few plants are infected, and a positive identification of the disease has been made, use of a fungicide is recommended. Even if a planting is defoliated by leaf blight, new buds are unaffected and the plants will usually emerge the following spring.