Introduction Most growers of ginseng are familiar with the typical symptoms of Alternaria infection . Stem infections occur as tan lesions that develop a coating of dark conidia or spores that rubs off on your hand like soot. The earliest leaf symptom is a chlorotic or yellow spot on the upper surface of the leaf which later becomes dry and tan. Under certain weather conditions Alternaria infections do not follow this pattern. If the weather has ben very hot and humid Alternaria infections take on a totally different look.
Affected leaves develop large patches that are dark green water-soaked.
These are visually identical to the early stages of foliar Phytophthora and Botrytis leaf blight. The symptoms of Alternaria infection in hot humid conditions resemble the symptoms of foliar Phytophthora blight and early Botrytis infection. This lesion began as a dark green water-soaked area and progressed eventually to a dark, dry, thin lesion. In a seedling garden symptoms of Alternaria infection in hot weather can be alarming. Plants quickly go down and are black from the straw up.