First report of Alternaria blight caused by Alternaria panax on Ginseng (Panax quinquefolius L) in Oregon and Washington, USA

Ginseng (Panax quinquefolius) is a high-value medicinal herb grown in relatively small commercial gardens in Oregon and Washington. Despite the limited acreage, ginseng represents a significant investment for growers since production costs are very high. In May 2000, necrotic girdling stem lesions about 2.5 cm above the ground were observed on two-year-old ginseng plants growing in the Willamette Valley of western Oregon. Tissues distal to the lesion had wilted, causing loss of foliage for the remainder of the year. The leaflets of some plants had brown lesions from which the centres had fallen out. Approximately half of the 0.25 ha garden was affected, with many plants severely infected. During the same month, similar symptoms were observed on ginseng plants in a commercial nursery in southwestern Washington.

The fungus Alternaria panax Whetzel was observed sporulating on leaves and stems of plants from both locations, and was isolated from symptomatic stem and leaf tissue onto both potato dextrose and water agar media. Identification of the pathogen was confirmed by mycologist Emory Simmons (Crawfordsville, IN). Outbreaks of Alternaria leaf spot of ginseng were observed again in western Oregon in 2001. Alternaria panax is a host-specific toxin-producing fungus and is a very destructive pathogen of ginseng. Widely distributed in the eastern and mid-western USA and Canada (Whetzel & Rosenbaum, 1912; Buonassissi & MacDonald, 1990; and Chang, et al., 1999), the pathogen has never been reported from Washington or Oregon. This report represents an expansion of the geographical range of A. panax, presenting a potential threat to successful ginseng production in the U.S Pacific Northwest.