ii4 Diseases of Truck Crops 



far as is known, no definite method of control can be 

 recommended. The use of healthy roots should be 

 depended upon. Wherever possible soil sterilization 

 with steam or formaldehyde is also recommended. 



Alternaria Blight 



Caused by Alternaria panax Whet. 



Blight is perhaps the most common of all ginseng 

 diseases. It is found practically wherever this crop 

 is grown. 



Symptoms. The disease at first manifests itself 

 as dark brown spots on one side of the stem. Often 

 the spots work in deep and cause the stem to rot and 

 break at the point of the lesion. On the leaves, 

 blight appears as watersoaked spots. These grad- 

 ually dry out, becoming thin and papery with a 

 distinct rusty brown border (fig. 19 n). The disease 

 may also attack the leaflets at the point of attach- 

 ment to the leaf stalk. This generally causes a 

 dropping and dying of the leaflets. Later a velvety 

 brown cover appears on the dead tissue which con- 

 sists of the spores of the fungus. Frequently the 

 seed heads are also infected. 



The Organism. The mycelium of Alternaria panax 

 is brown, septate. The conidiophores are erect, 

 brown, septate, irregular at the tips, and tufted. 

 The conidia are brown, borne in chains, and typical 

 of Alternaria (fig. 19 s). 



Control. Blight may be effectively kept in check 

 by spraying with a 3-3-50 Bordeaux mixture. 



