American ginseng (Panax quinquefolium) is a perennial herb native to parts of the US and Canada grown primarily for the medicinal properties of its root. Currently, more than 95% of the cultivated commercial ginseng in the United States is grown in Wisconsin. Wisconsin’s 150 growers cultivate 1500 acres of ginseng, producing 500 to 2000 pounds per acre which represents 10% of the world’s supply of ginseng. At an approximate average of $20-30/lb, ginseng is a high value crop for Wisconsin, totaling $50 to $75 million annually. Cultivated ginseng is grown on a raised plant bed under a tree or black woven polypropylene canopy. The shade required by the crop and dense plant spacing create a microclimate highly conducive to disease with limited air movement and extended leaf wetness periods. If Alternaria leaf and stem blight is not controlled, it can reach epidemic proportions within a month after the plants have emerged in the spring, destroying all the foliage. The loss in yield reported by Wisconsin growers when the disease is uncontrolled range from 50 to 100%, with the majority of those surveyed reporting losses of 75 to 100%.
“Alternaria blight, incited by Alternaria panax Whetzel, is the most common disease of ginseng throughout the world… This disease is a yearly problem for ginseng growers in Wisconsin and can be especially destructive, causing rapid defoliation and plant death.
In the absence of effective treatments for Alternaria blight, growers could potentially lose $13,930/ha in root revenue due to repeated crop defoliation. Since A. panax also infects drupes, seed may be threatened. With an average seed yield of 337 kg/ha, growers could lose an additional $18,537/ha (current market value $55/kg) due to Alternaria blight.
Cultural strategies to manage Alternaria blight include increasing plant spacing to enhance air circulation, removing infected foliage, and replacing straw mulch in affected areas. Unfortunately, these strategies are not practical and would not preclude the reintroduction of inoculum via air currents. The use of biocontrols as alternatives to traditional fungicides has also been considered for Alternaria blight management. However, the biocontrol agent did not adequately reduce disease under field conditions due to poor survival on leaf surfaces.
Currently, growers rely on fungicides to protect their crop from Alternaria blight. Growers must apply fungicide sprays judiciously during the relatively long growing season of May through September to protect the crop and comply with product labels.”
Authors: Hill, S. N., and M. K. Hausbeck.
Affiliation: Michigan State University.
Title: Factors influencing airborne conidial concentrations of Alternaria panax in cultivated American ginseng gardens.
Source: Plant Disease. 2009. 93:1311-1316.