This is the first ginseng crop update of the 2020 growing season. This spring represents some unique challenges for ginseng production. The primary concern is the availability of labour and the timing of pulling shade over the gardens. There are also the normal weather-related challenges to deal with.
The combination of a mild winter, lack of frost in the ground, and a warmer than normal March and early April has resulted in earlier than normal plant development. Based on development of other perennial plants at this time, it is likely that ginseng emergence so far is about a week earlier than normal. Compared to the last few years, plant development at this time is likely around the same stage as it was in 2017, two weeks ahead of 2018, and about 1 week ahead of last year. However, colder than normal temperatures are forecast in the next two weeks, and ginseng emergence will likely slow back to normal by the end of this period.
With tops of older roots starting to emerge from the soil below the straw, they can be vulnerable to low temperatures well below freezing if the straw layer is not thick enough. In 2016, following a mild March, a series of very cold nights from -10 to -12oC was suspected of killing some tops in older gardens in areas with thin straw cover. Because the damage was early enough, secondary buds still grew from those roots, but tops were much smaller than they should have been. Temperatures this week are forecast to be as low as -5 to -7oC. Unless the forecast changes, damage to ginseng should be minimal, but it is something to consider if emergence is poor or tops are smaller than normal in some areas of a garden.
The timing of putting shade over the gardens affects two things: frost and sunlight. It will be several weeks before any age of ginseng develops enough to require shade cloth for light protection. Light protection is generally required once the tops emerge from the straw and leaves begin to unfold but before they turn upwards. This will likely not occur until early May for older gardens based on current forecasts. At that point, damage will increase progressively each day without shade cloth, and tops will likely be killed by the light entirely by about May 20, depending on the weather. For 2s and older gardens, the canopy will re-emerge the following spring, but be smaller than it should have been a year earlier. Seedlings are the slowest to emerge but would be killed entirely if tops are killed by excess light. Generally, plants become sensitive once the forest canopy begins to close.
The other risk to consider is frost. The shade cloth normally provides a small amount of protection from ground frosts. Once the tops emerge through the straw, about two weeks before they are sensitive to light, they can be damaged by temperatures on the ground below about -2oC. Air temperature measurements are usually collected at 1.5 m off the ground, and air temperature forecasts are based on this level. On a calm, clear night the temperature on the ground can be 3 or 4oC colder at the ground level. So, without any protection, damage to ginseng can occur when air temperatures are forecast to be up to +2oC once the tops emerge through the straw. These temperatures can easily occur in late April or early May. If the shade cloth provides a couple degrees of protection, air temperatures would have to be 0 to -2oC to damage the tops, which is less likely at that time of year.
While nothing can substitute the light blocking effect of the shade, there are alternative methods to protect against frost. However, all of them require some labour or equipment to employ.
- Row covers – Most growers have row covers for frost protection and these can also provide a couple degrees of protection (Fig. 1). Growers will have to determine if the row covers can be put out more easily than the shade with limitations on labour.
- Overhead Irrigation – Irrigation during the freezing period can also protect the crop but increases the risk of root disease and requires the irrigation to be already set up ahead of time. In this method, the overhead sprinklers need to be turned on before temperatures at ground level get close to freezing and run continuously until the temperatures go a few degrees above freezing again in the morning. Ice would build up on the plant material (Fig. 2), but as long as the irrigation is running, it would stay at 0oC which is not cold enough to damage the plant material. With this method, there also needs to be capacity to irrigate all the acreage of ginseng at once.
- Wind Machines – Wind machines can be used to draw warmer air from above and blow it down to the ground. They are only effective during temperature inversions on calm and clear nights. There are portable wind machines available, but supply is likely limited, and this may only be an option for a few growers.
Crop protection is also necessary during this time to avoid losses later. Fungicide sprays need to begin when the tops begin tenting or pushing through the straw. This includes fungicides for both Phytophthora and Alternaria/Botrytis.
- For Phytophthora, Orondis Gold is often recommended when tops begin emerging through the straw and can only be used once per growing season. This product is now available as a pre-mix instead of a co-pack. It is recommended that the product be further tank mixed for resistance management. Consult the registrant (Syngenta) and the labels for compatible, registered tank mix partners.
- For Alternaria and Botrytis, there are many options available. However, keep in mind that chlorothalonil products (Bravo, Echo) can only be applied twice during the growing season beginning this year, with a further application as the last application in the fall. The rotation of products for Alternaria and Botrytis control will have to be adjusted accordingly.
It is also important to think of insect control in the spring. Activity of slugs should be low under the temperatures forecast this week. If you are concerned about whether slugs are active in your field, a beer trap is the best method to determine their presence and activity. A beer trap consists of a shallow tin, pan or lid buried to the rim and partially filled with beer. Put it out in the evening and check the next morning for slugs in the tray. If they are present and ginseng has emerged enough to be damaged above or within the straw, then apply slug baits. Cutworms are also a spring issue but will not be a problem over the next couple of weeks while temperatures remain low.