68 DISEASES OF GINSENG. 



tainly not in the case of the Alternaria Blight. These external 

 factors, especially the weather, do, to a marked extent, influence 

 the severity of the malady. The spores of the fungus not only 

 require moisture in which to germinate, but that moisture must 

 continue long enough on the leaves or stems so that the tender 

 germ-tubes may have time to penetrate the host plant and become 

 established as mycelium in the tissues. Just how long is ordinarily 

 required for this to take place, is not known but experiments indi- 

 cate that probably not less than 24 hours of cloudy rainy weath- 

 er, or heavy dew is necessary. It requires from four to nine 

 days for the diseased spots to make their appearance after infec- 

 tion. Cloudy, rainy weather is favorable to the rapid development 

 of the spots, even after the fungus is established within in the 

 tissues. Heavy showers of short duration, followed by bright 

 sunny weather, are not especially favorable to the blight. It is the 

 cloudy rainy periods continuous for a day or so, that favors an 

 epidemic of the disease. The relation of temperature to the devel- 

 opment of the disease has not been worked out. Growers gener- 

 ally hold, that "hot" weather brings blight. True it is, that the 

 malady seems to develop most destructively during the hot months 

 of July and August, but only when there is sufficient moisture. 

 The seasons of 1907, 1908 and 1909 were generally hot and dry and, 

 except in localities where there was a rainy period, Alternaria 

 Blight caused relatively little loss. As is the case with many 

 other parasitic fungi, it is quite possible that a drop in tempera- 

 ture, accompanying a rain period during the hot season, is favora- 

 ble to infection by Alternaria panax. 



There has been much discussion by growers as to the rela- 

 tion of different types and amounts of shading to the blight. By 

 some the question of mulch has been regarded as a controlling 

 factor. The writer must confess that none of these theories appear 



