There have been multiple reports over the past week of random plants wilting especially in 2-yr old gardens (Figure 1). These plants emerged relatively healthy and are now completely collapsing. The roots are shrivelled but with no signs of disease on the taproot. However, fibrous roots are mostly absent and browning where present. Some of the plants have a shrivelled stem below the straw without any apparent damage to the root.
The cause of this issue is unknown so far. In the past this has been attributed to Fusarium. Looking back in my records, the last time similar symptoms were reported was in 2005 and there are some similarities in the weather conditions between this year and that year. First, both winters were mild, but with some major fluctuations in temperature. At Delhi, the high temperature on Jan. 13, 2005 was 17oC which was followed by 5 nights with a low temperature below -25oC from Jan. 21 to 28, 2005. Major temperature fluctuations continued for the remainder of the winter and early spring. This was followed by an early June of that had numerous days over 30oC and very dry weather in May and June of that year. Flash forward to 2016 and we had a high temperature on Feb. 3 of 14oC followed by a low temperature of -25oC on Feb. 14. A very warm March this year was then followed by a very cold start to April with a low of -10oC as late as April 10. We are also experiencing a very dry spring and hot temperatures over the past week, similar to 2005.
The relatively mild winters on average would have decreased the hardiness of ginseng roots. The rapid changes in temperature, especially with the low snow cover we had this past year could have resulted in direct freeze damage of roots in areas with low straw cover. In addition, roots that were beginning to sprout after the mild March along with their tender stem tissue could have had heavy damage from the cold snap in early April. If this is the case, then damage would be most likely in areas with low straw cover, low areas prone to frost, and exposed areas open to the prevailing winds on those cold days (N to NW side of hills, beds etc.).
The potential of this damage to be caused by cold temperatures this winter and spring is supported by the fact that 2-year old roots are closer to the surface than older roots and would be more exposed to the cold. Also, some of the damage has been reported in areas that were heavily damaged by frost last year. Some of the roots showed damage only to the upper taproot and crown, with healthy tissues beneath. Finally, in our research garden, which had low straw cover, we have seen a lot of damage with most of the damage on the shoulders of the bed where straw cover would be the lowest. Damage is also more prevalent on the west side of the beds, which are more exposed to the prevailing winds. It is likely that the hot temperatures over the past week have stressed the plants enough to collapse due to the lack of fibrous roots.
The other possibility is that the temperature fluctuations have stressed the plants and made them more susceptible to root diseases including Fusarium. A combination of the disease and cold stress is more likely. A sample of the roots has been submitted to the Pest Diagnostic Lab to determine what pathogens may be present.
Regardless of the cause, there is not much that can be done to recover plants that have already collapsed. It is unlikely that this is the type of disease that will continue to spread to healthy roots, and control measures above what is normally done in a ginseng garden are probably not necessary. The damage is probably already done. However, if more information becomes available on the cause of the issue, I will report it in a subsequent crop update.
With the hot and humid weather Alternaria leaf and stem blight is showing up in multiple gardens. Damage is localized and minimal so far, but the crop should be protected to prevent spread since spores are likely flying from the few lesions that are present. Foliar Phytophthora has been reported as well, but would be localized to areas that experienced heavy rains in thunderstorms. More often, tops are wilting down due to Phytophthora root rot.