Ginseng harvest is in full swing and tops are senescing rapidly at this time. For gardens not being harvested this year, it is important to consider one last protectant fungicide over the next few weeks before winter. Foliar diseases like Alternaria and Botrytis will have no impact on root development this late in the season. However, inoculum from this year can remain on dried ginseng stems and in the straw over the winter. These could start new infections in the spring. In addition, root diseases like Rhizoctonia and Cylindrocarpon can continue to develop and spread under the cool conditions of late fall and early spring. It is a good idea to apply a broad spectrum fungicide to control diseases on both the remaining stems and in the soil before winter.
The product to use will depend on what issues developed in the garden this summer. If Alternaria was the main issue, consider an application of Allegro or Scholar, which can control Alternaria and Botrytis but also affect root pathogens. In addition to foliar blights, Allegro is registered for control of Rhizoctonia, while Scholar is registered for control of Rhizoctonia and suppression of Cylindrocarpon. If Alternaria was not a major issue and Phytophthora or Pythium were bigger issues, consider a Maestro application, which is registered for control of Botrytis, Phytophthora, Pythium and Rhizoctonia and suppression of Cylindrocarpon.
There are several reports of rusty root on seedlings this fall. This issue is quite common, but affected roots appear to have more damage than usual this year. Affected roots are often bright orange with the outer layers of the root crumbling off of the exterior (Figure 1). The tops of affected plants often turn reddish and senesce prematurely (Figure 2). Observations from research plots suggest that the condition may be more severe in portions of the bed exposed to higher rainfall rates, such as where rainwater drips off of the shade cloth. The causes of rusty root are not fully understood, but Fusarium and weaker strains of Cylindrocarpon may be involved. Abiotic issues such as nutrient deficiencies or toxicities could also be a factor. Excessive amounts of rainwater under the drip lines may result in nutrients leaching out of the root zone. Now is an ideal time to survey gardens for damage, since the early senescence is currently more obvious than other times of year. Dig up suspected plants to examine the root damage. Identifying the pattern of damage in the field can help in determining the cause and may point to potential management options. A sample of affected roots has been sent for further diagnosis.