Ginseng has been slow to emerge this spring but older gardens are greening up rapidly (Figure 1), while seedling gardens have not yet emerged through the straw. Ginseng at this stage in older gardens is highly prone to the development of foliar Phytophthora and other foliar diseases in periods of wet weather. Growers should ensure protection of these plants from Phytophthora, Alternaria and Botrytis. Botrytis is more of an issue if there is some existing damage on the plants such as slugs, sandblasting, frost or other diseases. Slugs will also be active during this wet period.
Growers now have several options to control foliar diseases of ginseng with the registration of many new products over the past couple of years. It is essential with these products to not apply the same product in two or more consecutive applications. Many newer products are more prone to fungicide resistance and rotating them with other products from different fungicide groups will delay or prevent the development of resistance. In some cases, two or three consecutive applications is enough for the fungus to development resistance and no longer be controlled by the fungicide. Rotation is also necessary if the same product is applied for two separate diseases. For example, Allegro is registered for control of both Alternaria and Botrytis. Even if the first application is for Alternaria and the second application is for Botrytis, resistance can still develop since both pathogens will be exposed in each application. Resistance only has to develop in one field one time and the product could be lost to the industry. Careful management of these products will ensure disease control options are available for the long term.
A listing of the fungicides registered on ginseng and their fungicide groups are included in the 2014 Crop Protection Guide for Ginseng (Supplement to Publication 610). All OGGA members received a copy of the guide in the most recent OGGA newsletter. Contact Sean Westerveld at firstname.lastname@example.org if you have not received a copy.