American Ginseng Production Would be Devastated Without Fungicides

Ginseng Under A Canopy

Ginseng Under A Canopy

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[12]:1311-1316.

Carrots are Unharvestable Without Fungicide Use

Unharvestable Carrots

Harvesting Carrots

Alternaria leaf blight is the most common foliar disease of carrot. Under optimal conditions, severe foliar epidemics rapidly develop, leading to loss of foliage and reduced yields. Alternaria also indirectly reduces yields by interfering with mechanical carrot harvests. Leaves weakened by blight break off when gripped by a mechanical harvester and the roots are left behind in the ground.

“Because high humidity and frequent rainfall or irrigation is common during the growing season, yield-threatening foliar blights are a recurring problem for carrots. …Michigan growers harvest carrots mechanically and weakened foliage can disrupt harvest due to carrot tops breaking off during lifting. In situations where foliar disease is severe and not controlled, the tops may be compromised to the extent that the crop cannot be harvested. Therefore, fungicides currently play a critical role in the management of foliar diseases.”

Author: Hausbeck, M.K.
Affiliation: Michigan State University, Department of Plant Pathology
Title: Carrot Disease Update
Source: Carrot Country. 2012. Summer:6-8.