Some areas were touched by frost on the night of May 13, but it is too early to determine the extent of the damage. Damage would be mostly confined to low areas of gardens with poor air flow. With temperatures expected to warm considerably over the next day, there is a higher risk of Botrytis developing in areas affected by frost. Botrytis usually requires damaged plant material in order to infect a plant, and warm and humid conditions favour the spread of the disease. A protectant fungicide should be applied to any areas damaged by frost.
Alternaria pressures were high in 2012 and there may be higher levels of inoculum on old stems this year. Alternaria is also favoured by humid conditions and previous damage. A foliar fungicide program should ensure protection from both diseases at this time. Growers now have many options for controlling Botrytis and Alternaria in ginseng. Consult the 2013 Crop Protection Guide for Ginseng (Supplement to Publication 610) for a list of registered products. A rotation of registered products is necessary to avoid the development of resistance.
Over the past several years the first report of foliar Phytophthora has occurred around this time of year. Growers should closely monitor gardens for any symptoms of foliar Phytophthora. Conditions have been relatively dry in many areas so far this month, which reduces the risk of Phytophthora. However, more rainfall is in the forecast. Gardens should be protected before a rain. At present, Ridomil and Aliette are the only registered products for control of Phytophthora in ginseng. If you suspect you have foliar Phytophthora please report it to me at firstname.lastname@example.org.