White Potato 203 



water-soaked areas on the leaves and in wet weather the occur- 

 rence on their under surface of a white mildew are characteris- 

 tic of late blight. The disease spreads rapidly, the blighted 

 plants giving off a disagreeable odor. Irregular discolored 

 lesions, which later become somewhat sunken, appear on the 

 tubers. It is in these diseased tubers that the fungus lives 

 over winter. Control: Spray with bordeaux mixture 5-5-50, 

 beginning when plants are six inches high and repeating 

 every ten days to two weeks throughout the season. Insecti- 

 cides may be added directly to the bordeaux. Potatoes in 

 blighted fields should not be dug until the vines, are dead 

 and dry. 



Eakly blight (Alternaria solani). — Irregular dark brown 

 spots that show concentric rings develop on the leaves, and 

 premature death of the foliage may result. Control: Thor- 

 ough spraying with bordeaux mixture 5-5-50 will afford con- 

 trol. Applications should be begun early. 



Scab {Actinomyces chromogenus) . — ^The disease is due to 

 a parasitic bacterium that attacks the skin of the potato 

 tuber, causing rough corky areas. The organism not only over- 

 winters on the tubers but also in the soil and manure. Goru- 

 trol: Uncut tubers should be soaked for 114 hours in a 

 solution made by adding 4 ounces of powdered corrosive sub- 

 limate to 30 gallons of water ; spread them out where they 

 will dry quickly. It is important to use wOoden containers 

 for the solution, and tubers should preferably be treated before 

 sprouts have developed to any great extent. 



Khizoctonia (Rhizoctonia solani). — The most easily rec- 

 ognized symptoms are black scurf on the surface of affected 

 tubers, reddish brown cankers on young sprouts, dwarfing or 

 rosetting of vines, and the prodiyjtion of numerous small ill- 

 shapen potatoes. Control: The treatment of seed tubers with 

 corrosive sublimate as recommended for potato scab is advis- 

 able. Crop rotation is important. 



Black wakt (Synchytrium, endoMotica). — Hough warty 

 outgrowths are produced on the tubers, especially at the eyes, 

 and may occur on other underground parts of the plant as 



