Ginseng fields are beginning to dry out, but the wet conditions have left significant issues with Phytophthora root rot. Any additional rains with the approaching cold front could increase spread of the disease.
Rhizopus continues to be an issue in 2-yr gardens. Because the roots are destroyed by the time foliar symptoms appear, and the disease does not appear to spread from root to root, control of this disease is not necessary at this time. There are no products registered for control of Rhizopus in ginseng, and Rhizopus may not be the initial cause of the issue. It is possible another fungus causes the initial damage and Rhizopus takes over and rots the remainder of the root. Growers should continue to monitor gardens to ensure the disease does not begin to spread to neighbouring roots.
The hot and humid conditions over the past week have increased Alternaria leaf blight activity. Alternaria infection is most severe on weakened plant materials. The wet conditions over the past few weeks have increased drip-line issues and these will be hot spots for Alternaria activity. Growers should promote good air flow through gardens by lifting the side shades to reduce humidity in and around the canopy and allow hot air under the shade to escape. Temperatures under the shade are up to 6oC warmer than ambient air, and this can stress plants and leave them more susceptible to infection. Hills entirely contained under a shade can be especially hot as the hot air rises up the hill and pools under the shade. Inserting a vent in the shade at the top of the hill will allow the hot air to escape more rapidly. Once plants are weakened by an initial lesion, the plant becomes even more susceptible to subsequent infection. The interval between Alternaria controls should be reduced under these conditions to the low end of the range indicated on the product label.