Part II.] 



POTATO DISEASES. 



127 



See general spraying 

 In addition to spray- 



FiG. 3. — Late blight rot of tuber. 

 (After Cornell Experiment Sta- 

 tion Circular No. 19. ) 



Control. 

 directions, 

 ing, — 



1. Allow no decayed or partially 

 decayed seed to go into storage. 



2. Select clean seed tubers, 

 known to have come from healthy 

 vines. 



3. Store in a fairly dry, cool 

 place. 



4. Avoid planting on wet, 

 poorly drained land, or where the blight was serious the previous 

 year. 



Scurf or Rhizoctonia. — This disease has become prevalent 

 throughout Massachusetts. It appears on the surface of the tuber 

 as small, black, hard bodies called sclerotia, which appear like 

 particles of soil but are not easily rubbed off (Fig. 4). In severe 

 cases deep pits resembling wire-worm injury may be produced. 

 The real serious phase of the disease occurs on the young shoots, 

 which become affected from seed tubers. On the lower part of 



these shoots dark de- 



cayed spots or streaks 

 appear, often causing 

 death even "before the 

 shoots appear above 

 ground (Fig. 5). When 

 this occurs new sprouts 

 usually develop, but 

 these in turn are likely 

 to be killed or weak- 

 ened by the disease. 

 Affected shoots which 

 are not seriously 

 enough diseased to be 

 killed develop into 

 weak, sickly tops. 

 The so-called "little 

 potato disease" is a 



phase of this trouble. Fiq. 4. — Scurf or Rhizoctonia, showing blaclc sclerotia on 



tuber surface. 



