DISEASES OF CROPS 



959 



Treatment. — Soak the seed potatoes for two hours in formaldehyde 

 (1 pound in 30 gallons of water) or in corrosive sublimate (4 ounces in 30 

 gallons of water) for one and one-half hours. When the land becomes 

 infected, avoid the use of stable manure and lime, and rotate crops for 

 three to five years. 



Little Potato, Rosette, Stem Rot, Scurf (Rhizoctonia or Corticium 

 vagum, B. and C, var. solani, Burt.). — This disease assumes different forms, 

 varying with the climatic conditions, soils and varieties. In very severe 

 cases many of the young plants fail to get through the ground. Many 

 that do get through are dwarfed and show a peculiar crinkling of the 

 foliage. The part of the stems 

 below ground shows peculiar 

 brownish or black cankers. In 

 some cases the leaves tend to roll 

 upward; many small tubers are 

 formed just below the surface of 

 the ground and just above a very 

 pronounced canker, and aerial 

 potatoes along the stem above 

 ground. The fungus can be 

 readily detected on the tubers; 

 it appears as small black spots, 

 which do not wash off, but can be 

 readily removed by rubbing. 

 However, the presence of these 

 spots on the tubers does not 

 necessarily mean a severe out- 

 break of the disease. 



Treatment. — Soak seed pota- 

 toes in corrosive sublimate as 

 recommended for scab. 



Bacterial Wilt (Bacillus sol- 

 anacearum, Smith). — The plants wilt prematurely, become yellow, then 

 black and dry. This disease attacks tomatoes, tobacco, peppers and 

 eggplants. 



Treatment. — Rotate crops, avoiding those that are susceptible. 



Tipburn. — This disease is due entirely to hot, dry weather. It causes 

 the leaves to dry at the tips and margins, roll up and break off. 



Note. — There are a number of other diseases of the potato which 

 cannot be included in this brief discussion. 



A Potato Affected with Russet Scab. 1 



.Showing the russeting and cracking, asso- 

 ciated with the fungus Rhizoctonia. 



TOMATO 

 Early Blight. — See Potato. 

 Leaf Blight (Septoria ly coper sici, Speg.). 



-This disease appears as 



1 From Farmers' Bulletin 544, U. S. Dept. of Agriculture. 



