There have been many more reports of leaf roller damage to ginseng over the past week. At this point the caterpillars are already quite large and may have begun to pupate. The only product registered for control of leaf rollers in ginseng is Dipel 2X DF and a maximum of 2 applications are allowed per season. Dipel is most effective when the caterpillars are young, and would not be as effective at this stage of development. Since they are close to pupating, they may not be doing much more feeding and the cost of a Dipel application may not be worthwhile.
Not much is known about leaf rollers in ginseng and the exact species have not been determined. There may be more than one generation of leaf rollers per year, or there may be different species attacking at different times of year. Growers and garden walkers should continue to monitor gardens closely for young larvae. By the time the damage can be seen from a distance it may be too late to effectively control the caterpillars. Closely examine plants at various locations in each garden, both above and below the leaf for the tiny developing caterpillar. At this stage there may not be any rolling of leaves. Once caterpillars are found, determine the extent of the problem and whether a spot application would be sufficient to control the problem. Dipel 2X DF is effective when caterpillars eat treated leaves and is best applied in the evening when caterpillars are coming out to feed on the ginseng. Drop nozzles are recommended to ensure thorough coverage of both the upper and lower surfaces of the leaves. Since only 2 applications are permitted per season, growers should use the product only when it is effective and the benefits outweigh the costs to avoid the development of resistance.
New damage continues to show up in older gardens from the freeze in late April. With the wet conditions over the past week, these newly affected tissues will be prone to the development of Botrytis. Growers should apply protective fungicides in any gardens in which fresh damage is identified.
Some ginseng growing areas have now received enough rain that standing water in gardens is an issue. These areas of gardens are very prone to the development of foliar Phytophthora. These same areas have received at least two potential infection periods for Phytophthora. A further infection period could result in more widespread incidence of the disease. While Aliette can provide protection in healthy tissues, Maestro application is recommended if foliar Phytophthora appears in the garden or in the area.