Ginseng growers continue to report loss of 2-year old ginseng plants to the disease known as Rhizopus, but the disease does not appear to spread from root to root. It is likely that Rhizopus is not the primary cause of the disease. The initial cause of the issue is likely a seed-borne issue such as Fusarium. Fusarium has been isolated from diseased roots. It is possible that Fusarium weakens the plant and allows an entry point for secondary rot organisms to move in and destroy the root under wet conditions. Rhizopus is only one of several different rot organisms. Pseudomonas, a common soft rot bacterium, has also been isolated from diseased roots. Once symptoms develop there is nothing that can be done to control the disease. Control may not be necessary, since the disease does not appear to spread from root to root.
Symptoms of heat stress are being reported in many areas. This is likely the result of days of hot sunny weather and little air movement. The only way to control this issue is to allow hot air to vent out of the garden through the shade on hot days and ensure good air movement through the garden by raising the side shades. The best time to consider improving airflow through the garden is at the time the shade is being erected in the seeding year. This includes allowing areas where the shade can be raised in high risk areas, or establishing roadways across the top of a hill. The areas of the garden that are most at risk of heat stress are at the top of hills contained below the shade and those gardens erected close to forests or wind-breaks where the prevailing winds are blocked on hot days.
With the return of drier weather and dew periods getting longer each day, the risk of Alternaria will increase again. This includes the developing berries, which are vulnerable at this stage of development. Thorough coverage of all above ground surfaces of the ginseng plant is essential for protection from Alternaria. Research has shown that the use of drop-arms is necessary to ensure coverage of the stems and the underside of the leaves.
Rusty root is also present on ginseng seedlings. Scattered roots show an orange rust of the entire root surface. This disease has been shown to be caused by several different fungi including Fusarium, Cylindrocarpon, and Rhexocercosporidium. Once symptoms develop there is not much that can be done to control the disease. These diseases can be seed borne, and seed treatments can be an effective method of reducing disease pressures. Apron XL LS and Maxim 480 FS are the only seed treatments registered for use on ginseng. Maxim provides control or suppression of Fusarium, Cylindrocarpon and Rhizoctonia, while Apron provides control of Pythium.