Other than localized damage from summer storms, weather conditions to this point of the season have been ideal for ginseng production with seasonable temperatures and only timely rains, which is in contrast to the excessive rains last year. The biggest issue growers are dealing with is left-over root phytophthora issues from last year. Alternaria is a constant battle, but outbreaks of disease are often a result of poor spray coverage, lack of timely fungicide application, or improper choice of fungicide. No major insect issues have been reported over the past few weeks.
Grub Control at Seeding
Seeding is occurring and will continue over the next few weeks. Many growers are accustomed to applying imidacloprid (Admire/Alias) at seeding to control grubs. A reminder that this product will no longer be registered for this purpose on ginseng after May 19, 2025. There are many growers that do not apply Admire at seeding and report minimal issues with grubs. It appears that grub issues can be patchy and major issues may only occur under certain production practices. Fumigating prior to the egg-laying period of European chafer adults in mid- to late-June will prevent control of the eggs and early instar grubs. Weedy fields between fumigation and seeding may entice egg-laying in the fields.
Since growers will have no options for management of this pest after May 19, 2025, now is the time to determine how much benefit the insecticide application is providing and look for alternative methods (e.g. adjusting fumigation timing, weed management) to manage the pest. Consider leaving a section of the field untreated to help determine what impact the insecticide is having in the field.
Root Disease Management
Root phytophthora will progress as long as the soil remains moist and soil temperatures are above the minimum for the fungus (around 7°C). Progression will be slow when soil temperatures drop below around 15°C. Some progression of the disease can be expected to continue until mid-October and this is not influenced by the state of the tops. Even when the tops are dead, the fungus can still progress.
Cylindrocarpon root rot can accelerate under cool soil conditions. Most of the disease development appears to occur in the fall and spring when ginseng is not actively growing because of its preference for cool temperatures.
Continue to monitor for and manage these two root diseases in the fall.
Foliar Disease Management
Alternaria is still a major risk in late summer, but the consequences of the disease are lower at this time of year, since the tops will be senescing anyway over the next month, and as a result, the lost yield potential from leaf death is lower. However, outbreaks late in the summer can result in increased inoculum that is available to start new infections in the spring.
Botrytis risk is typically low at this time of year but will increase anytime the canopy is damaged by another pest or a weather event (e.g., wind or hail). Unlike Alternaria, Botrytis is an extremely common pest of most crops. As a result, there is minimal added risk from inoculum overwintering on crop debris. It is best to focus on Alternaria at this time of year, and if concerned about Botrytis, apply products that manage both diseases well. Use targeted fungicides for Botrytis alone only if the cost of fungicide application is justified by the potential losses of root growth (i.e., if there are still many weeks of green growth and active photosynthesis ahead).
Last year at the end of August growers were noting significant damage from fall armyworm in rye crops grown ahead of ginseng or as nurse crops in newly seeded gardens. It is important to monitor for this insect pest before damage becomes obvious and it is too late to control them. Coragen can be applied to newly seeded gardens to control armyworm but will only be effective when caterpillars are small (less than 2.5 cm or 1 inch in length). Refer to this previous article for more info.