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Ginseng Disease Alert: Essential Prevention Strategies

Many of the ginseng growing areas over the past week. Root and leaf diseases of ginseng may increase where areas experience heavy rains and very humid conditions, unless steps are made to prevent disease now. The conditions over the past week are ideal for the development of diseases such as foliar Phytophthora and Botrytis, and there is the continued threat of Alternaria. In addition, saturated soils provide ideal conditions for rapid spread of root diseases, especially Phytophthora root rot.

At this point it is essential to do as much as possible to avoid significant losses due to disease:

Increase Airflow: Although raising the side shades can damage the plants near the edge, the increased airflow would be beneficial by decreasing humidity and leaf wetness in the canopy, and reducing foliar diseases. It would also help to dry out the straw and soil more rapidly, reducing the spread of root diseases. Growers should seriously consider this option, since in many cases leaves in the canopy have been wet for four days straight and protective fungicides will have been washed off of the leaves if heavy rainfall has occurred in your area.

Removing Surface Water: In areas with saturated soil, subsoiling in the trenches can increase water flow and cause surface water to drain more rapidly. This could greatly reduce the chances of splashing water contaminated with Phytophthora onto plant surfaces. Once foliar Phytophthora becomes established it can be very difficult to control, especially in these conditions. It is also necessary to add straw to saturated trenches to reduce splashing. In many cases it can be difficult to remove enough water using these strategies. It may be necessary to dig trenches and catch basins to ensure movement of water away from gardens.

Sanitation: It is especially important under these conditions to limit entry into fields when the leaves are wet or the soil is saturated. Foliar diseases are already present in many fields. Spores of these fungi can easily be picked up on clothing or machinery when the leaves are wet, and spread down the rows or to other gardens. In addition, root diseases can be spread on boots and machinery. Ensure sterilization of boots and machinery when leaving a diseased garden.

Chemical Applications: Maestro (captan) is the only product proven to work in heavy rainfall/saturated soil conditions for control of Phytophthora.
The heavy rains we have experienced over the past week in most areas will have washed fungicides off of leaves. In addition, once there have been multiple inches of rain, fungicides normally used to protect the roots will be leached out of the root zone, removing this protection.

If Prevention Does Not Work:

In some cases, root rot may already have taken over areas of the field. In these cases, it may be helpful to remove the shading in the areas already lost to disease to prevent the spread of diseases such as foliar Phytophthora from these areas to healthy areas of the garden. However, if the soil is saturated, root diseases will still be able to spread even if the tops are killed.

If the wet conditions persist over the next few weeks, some growers in the worst hit areas may have to consider cutting their losses and harvesting early. In saturated soil, root rots can completely destroy a root in 7 days. The spread of these diseases will be very rapid under these conditions. The roots will have at least recovered the shrinkage from the spring at this point in the season. Monitor your crop closely over the next few weeks to determine the extent of root diseases.