Foliar diseases are the major issues facing ginseng at this time. Alternaria has been spreading in gardens and targeted Alternaria fungicides should be applied (Figure 1). Phytophthora leaf blight has been present for a few weeks and wet conditions will allow it to continue to spread. It is important to distinguish the symptoms of Phytophthora leaf blight (Figure 2) from those of Phytophthora root rot (Figure 3). While they are caused by the same pathogen, the location of the pathogen will determine which products will be most effective. Phytophthora leaf blight is far more destructive because air-borne spores can spread the disease throughout the garden and beyond. Growers now have several options for control of/protection from the disease in both the tops (Revus, Reason, Acrobat, Aliette) and in the roots (Maestro, Ridomil Gold, Aliette, Reason, Revus).
Figure 1. Developing Alternaria leaf blight lesions on ginseng within the past week.
Figure 2. Phytophthora leaf blight in June 2014 with water-soaked dark sections of leaf or whole leaflets. If the upper stem is affected the whole top can droop (see Figure 3).
Figure 3. Symptoms of Phytophthora root rot on the leaves of ginseng. The upper plant in the photo probably had foliar infection due to the dark water-soaked appearance, but the lower plant is wilting down due to Phytophthora root rot alone.
When spraying for multiple diseases at the same time, it is necessary to choose a product rotation that minimizes the number of applications but maximizes control of each disease. A new table has been added to the latest version of the 2014 Crop Protection Guide for Ginseng which has been distributed to all growers through the OGGA Newsletter. The table titled “Activity of In-Season Fungicides on Ginseng Diseases” includes a list of fungicides registered on ginseng for in-season disease control and their level of activity on target and non-target diseases based on publicly available research trials and experience with these products in other crops. Revus and Reason were registered after the publication date and are not yet included in the table. The best strategy for disease control is to apply broader spectrum, less targeted products when conditions are less favourable for disease, and switch to more effective, targeted products when there is high pressure of a specific disease.
Since the available fungicides are registered for a limited number of applications per year, it is also necessary to plan your product rotation to ensure control of diseases over the entire season. For example, some products are only registered for 2 or 3 applications a year and these should be saved for periods when they will be most effective. Consult the 2014 Crop Protection Guide for Ginseng or the product labels for more information on the number of applications permitted per season and application procedures.
While insects are not a major problem for ginseng production, they can cause significant damage in local areas. Two insect pests that are most damaging this time of year are four-lined plant bug (Figure 4) and leafrollers (Figure 5). Now is the time to scout fields closely for these two pests. By the time you see significant damage it may be too late to control them with insecticides. For leafrollers, look for curled leaf edges with webbing inside and chewing damage to the leaves. For four-lined plant bug, look for regular shaped brown spots in the leaves or the insects themselves hiding under the leaves.
Figure 4. Adult four-lined plant bugs on lemon balm with typical spotting damage. Damage would be similar on ginseng leaves.
Figure 5. Curled leaves due to leafrollers in ginseng. Unfolding the rolls would reveal webbing, insect frass and possibly the caterpillar itself.