Dry weather conditions and low humidity during warm periods have reduced the risk of most diseases of ginseng. However, frost damage in some gardens and plant stress due to dry conditions can result in increased risk of Alternaria and Botrytis, so it is important to remain vigilant in managing foliar disease. These diseases, especially Alternaria, can explode when the weather changes to hotter and more humid conditions. Cooler temperatures over the next week will hopefully keep the risk somewhat lower. It is important to achieve good spray coverage and to use a rotation of effective products in preparation for higher risk of disease.
During periods of high foliar disease risk, it is important to understand the mobility and modes of action of the different fungicides you are using. Consider alternating between contact fungicides, which offer protection from new infections, with those that are translaminar (moving through the leaf), locally systemic, and/or xylem mobile (moving upwards and outwards from the point of contact). These usually provide some curative control when the pathogen has already entered the leaf. These products also compensate somewhat for less-than-ideal coverage of the plant surfaces, since they can move from treated areas (e.g., the top of the leaf) to areas that often have less coverage (e.g., the bottom of the leaf). However, there are no truly systemic products for management of Alternaria, so it is still very import to achieve good coverage of the stems, not just the leaves. This can be more difficult when the canopy is disrupted by frost damage (e.g., kinked stems). The use of drop nozzles down each alley is important for achieving good stem coverage for older gardens.
Figure 1 includes tables that were distributed at the Ginseng Industry Day in April providing a summary of all the products registered for use on ginseng as of last fall. I am not aware of any new product registrations since then. The fungicide table lists the mobility of the different products within the plant. More detailed information on many aspects of pest control product use in ginseng and other crops is provided in the Ontario Crop Protection Hub (Ontario.ca/cropprotection).
Figure 1. Ginseng Pest Control Product Summary Tables 2023
It is not normal to consider irrigation in ginseng at this time of year, but a complete lack of rain for the past 18 days and minimal rain in the two weeks before that, plus low humidity and generally sunny (or smoky) weather, have resulted in abnormally dry conditions. It is important to monitor soil moisture and ensure adequate irrigation. Irrigation decisions should not be influenced by forecasted rain events, since crop losses can occur before any rain occurs, especially if the forecasted rain fails to materialize. Consult this previous blog post for irrigation resources: https://onspecialtycrops.ca/2022/07/06/irrigation-scheduling-resources-for-ginseng-growers-ginseng-crop-update-july-6-2022/
The lack of rain could also affect the fertility of the crop. If you applied granular fertilizer, especially nitrogen, after the first week of May and have not irrigated, it has likely not made its way down to the roots yet. Foliar application of nitrogen is not adequate for meeting the nitrogen needs of the plant (although it could help in some situations reduce major deficiencies), so deficiencies could appear if nutrients from granular fertilizers were applied after any significant rain or overhead irrigation events. Fortunately, the lack of rain also virtually eliminates the leaching of nitrogen from the root zone, so anything that was applied earlier or is residual from last year will still be available. Consider overhead irrigation not only for meeting the water needs of the plant but also to move nutrients from granular fertilizers into the root zone, even if soil moisture is still adequate for ginseng. This is not an issue for growers that fertigate through a drip irrigation system.
Dry soil conditions can also affect the availability of some nutrients. Calcium deficiencies are known to occur in dry conditions because the reduced transpiration from the leaves means less water is moving through the plant. Since calcium moves into the root in this flow of water, less flow in dry conditions means less calcium entering the plant. This can lead to tip burn of the leaves and poor berry/seed development. Again, the solution is adequate irrigation, not the addition of more calcium.