Ginseng is showing definite signs of senescence in most fields. The focus of fungicide programs at this time of year should be to minimize inoculum for next season for foliar diseases and maintain control of root diseases. If gardens are ready to be harvested, there is not much point in keeping the leaves free of disease unless plants are still green and will not be harvested for several weeks. Root disease control may still be necessary in these gardens if rots are actively spreading, but growers should pay attention to pre-harvest intervals (PHI) listed on the label to ensure residues on the root are below established limits. Many ginseng products have PHIs in the range of 20 to 30 days, so they cannot be applied up to a month before harvest (Quadris has a PHI of 2 years). Choose products with shorter PHIs if sprays are necessary.
Botrytis spores are widespread in the environment, so control of Botrytis is less critical once the leaves are no longer photosynthesizing. Even if inoculum on stems and old leaves are controlled, spores will move in from outside of the garden in the spring. On the other hand, Alternaria panax only affects ginseng and a few related forest species that are relatively rare, so the garden is the primary inoculum source for next season. It is important to control the disease on dying plant tissues to reduce inoculum in the spring. However, if leaves are no longer green, there is no need to keep up with a regular spray interval. Control of spores can be achieved with a broader spectrum fungicide near the end of the season rather than repeated applications through the fall.
Root diseases like Cylindrocarpon and Rhizoctonia can be relatively active at low temperatures in fall, milder winters and early spring. Continued control of these diseases is necessary in gardens not being harvested. Phytophthora root rot is less active at cold temperatures but will still be active until the soils cool.
Harvest will begin soon and this is the first year that most growers will be harvesting gardens not fumigated with Telone C-17. We have been conducting a survey of fields treated with different fumigants to get a better idea of how the two main fumigants (metam-sodium and chloropicrin) are performing for various ginseng pathogens. Those results will be available this winter. Growers should keep track of the levels of various diseases in harvested root this year. This will aid in the selection of the best fumigants and fumigation practices for future gardens.