The freezing temperatures over this past weekend have resulted in damage to ginseng plants that had emerged out of the straw. The primary symptoms of damage will be kinking and splitting of ginseng stems as the plants unfold (Figure 1). There is also some water-soaking on affected leaves (Figure 2). This water soaking could be easily confused with a foliar disease. Most seedlings were still protected by the straw unless straw cover was very thin (Figure 3). The extent of the damage will not be known until plants have fully unfolded. With the onset of humid and warmer temperatures, the risk of Botrytis is high on damaged plant tissues. Alternaria could also develop, especially on weakened tissues. An application of a broad-spectrum foliar fungicide such as chlorothalonil (Bravo/Echo), Switch or Allegro is advised to protect the plants from both Alternaria and Botrytis. If Botrytis appears in a garden, Elevate can be used to stop the progression of the disease.
Gardens should be monitored very closely over the next two weeks for foliar Phytophthora. The first reports of foliar Phytophthora in the last several years have occurred in mid-May. Because plants are emerging ahead of schedule this year, foliar diseases may also develop early. Ridomil and Aliette are the only fungicides currently registered for control of Phytophthora in ginseng.
Figure 1. A split stem in a 2-year garden caused by the freezing temperatures this weekend.
Figure 2. Water soaking directly caused by freezing temperatures.
Figure 3. Seedlings emerging under the straw. These were protected from the freeze by the straw.