THE POTATO 197 



source of the trouble is from planting the potato 

 in fields that have previously shown the disease 

 within two or three years. Such soils are said to 

 be 'sick.' 



"A second period of destruction due to this 

 disease comes during storage. Tubers infected in 

 the field when stored under conditions of moderate 

 temperature are apt to show a high percentage 

 of dry rot. In such cases the fungus causes a 

 blackening of the tuber, with a final outbreak of a 

 whitish mold, and may serve to infect the wounds 

 in other tubers. 



"In the control of this widespread and destruc- 

 tive disease much emphasis should be placed upon 

 the use of tubers free from the disease. ('Bulletin 

 229,' Ohio Agricultural Experiment Station.) Ex- 

 periments have been tried with diseased tubers 

 which indicate that if the diseased portion is largely 

 cut away and the tubers treated with formalde- 

 hyde solution in water such seed will give 

 nearly as good results as tubers from healthy 

 plants. Potatoes should not be grown on the same 

 soil immediately following a crop of the same kind 

 which showed the disease. Experiments along this 

 line indicate that even a three-year rotation is too 

 short to make it safe. 



"Storage of the tubers is also an important mat- 

 ter. It has been found that storing in outdoor 

 pits is preferable to cellar storage, as a rule, and the 

 lower temperature at which the tubers are kept 

 under this method usually prevents, to some ex- 

 tent, the spread of the dry rot. Being a soil fun- 

 gus and capable of living for several seasons in the 

 soil of an infested field, no spray which can be ap- 

 plied to the part of the plants above ground is 

 effective in controlling the disease. " 



