Evaluation of TOM-CAST in Timing Fungicide Sprays for Management of Alternaria Blight on American Ginseng.

Alternaria panax incites blighting of the foliage, peduncles, and drupes of cultivated American ginseng (Panax quinquefolium). A disease forecaster (TOM-CAST), originally developed to predict leaf blight caused by A. solani on tomato, was evaluated for management of A. panax in commercial ginseng gardens. For 3 years, fungicide sprays initiated by TOM-CAST (using 10 and 15 disease severity value thresholds) were compared with sprays applied at 7- and 10-day intervals. Three fungicide programs were evaluated: (i) chlorothalonil alone, (ii) chlorothalonil alternated with pyraclostrobin, and (iii) copper hydroxide alternated with pyraclostrobin. As many as 10 fewer fungicide applications were made when using TOM-CAST or the 10-day programs. Although select TOM-CAST treatment programs were comparable with the 7-day schedule in limiting foliar disease, only the 7-day applications adequately protected drupe and seed yield. Both A. panax and A. alternata were recovered from drupe tissues and seed coats. Only A. alternata was recovered from endosperm halves. Ginseng seed yield and quality is an important consideration when assessing fungicide programs.