With the very dry conditions we are currently experiencing, it is extremely important to ensure you are irrigating ginseng enough. This is a critical time of year for root development, since leaves are still healthy and green. Any stress at this time of year can lead to early senescence, which can reduce root growth for the remainder of the year. It is especially important to irrigate sufficiently in seed production fields because water stress can lead to berry abortion and poor seed development. Water stress can also lead to more wind burn and heat stress and can make the plants more susceptible to foliar diseases.
Over the past few weeks Rebecca Shortt, OMAFRA Water Quantity Engineer has put out two irrigation articles to help in calculating your irrigation needs. The following article provides the calculations on water needs for the week. Crop factors for ginseng have not been established, but they have been estimated at 0.3 for seedling gardens, 0.7 for 2-year old gardens and 0.8 for 3-yr old gardens and older. This estimate is based on a fully grown ginseng crop using about 80% of the water a crop in an open field would use. You might think it should be a lot lower because of the straw mulch, the shading and the lower air flow in a garden. However, it is actually much warmer under ginseng shade, which would counteract much of the benefits of the mulch and the shade. High cloth shade and wood shade gardens would use less water because it is cooler under these structures.
For those with drip irrigation, it is often difficult to know how often to run the system and for how long each time. The following article provides examples for determining your drip irrigation needs:
How Long Do I Run My Drip Lines?
Despite the dry conditions, root diseases continue to show up. New infections of Phytophthora and Cylindrocarpon have been reported. Frequent irrigation can lead to wet spots where there are leaks in the system, where sprinklers overlap and near drip irrigation emitters. These can be localized sites of root infection. Do not forget about your root disease management!
The main problem with applying fungicides for control of root diseases at this time is difficulty getting the product to the root zone. For those with overhead irrigation, you can time your fungicide application before irrigation to move the product into the root zone. For those with drip irrigation, this is not an option. The only viable option in this case is to irrigate before spraying to wet the soil, spray at the highest water volume you can practically achieve, time the spray before a rainfall (even if it is only a few millimetres), and if rainfall is not sufficient, irrigate again to move the product around. In order for the product to be effective, it will need to get through the straw before drying, and there is no point in applying the product if this is not possible.