Many ginseng fields are beginning to show early signs of senescence, which includes a slight purpling of the leaves, especially in older gardens. Earlier senescence this year is probably a result of the frost damage to stems in May. The life of the plants can be extended by ensuring consistent irrigation, if needed, and maintaining a spray program to control Alternaria and Botrytis. Heat stress will also accelerate senescence, so it will be important over the next few days to ensure good ventilation in gardens.
Early senescence should not be confused with the foliar symptoms of a root disease. Tops on diseased roots will often turn more red or yellow, rather than purple and will stand out from the rest. In our research plots we are seeing considerable rusty root on seedlings this year (Figure 1), and leaves on affected plants are showing red and yellow leaf symptoms. Rusty root can be caused by several different fungi including Fusarium, weak strains of Cylindrocarpon, and Rhexocercosporidium. Controlling these fungi can be difficult. Both Scholar and Maestro are registered for suppression of Cylindrocarpon and may have some effect on Fusarium at the same time. Some seedlings may grow out of this damage in later years and others may die off completely. The stand is often thick enough in a seedling year to overcome the loss of a few plants and still form a full canopy in the second year.
Figure 1. Rusty root on seedlings in a new research garden.
When harvesting ginseng seed, it is important to avoid harvesting seed in heavily diseased areas. The berries in these areas may be infested with fungi like Fusarium. Infested berries can lead to seed infection in the field or during the depulping process. Berries can also be underdeveloped in diseased areas, which could lead to higher rates of seed disease during stratification if they are not removed. If collection of seeds from diseased areas is unavoidable due to the extensive frost damage, only intact and healthy looking berries should be collected.