THE RHIZOCTONIA DISEASE OF POTATOES. 21 5 



yields of Irish Cobblers in this section. It is well known that 

 yields of Irish Cobblers are frequently disappointing farther 

 west in the central part of the State, where good crops of 

 Green Mountains and certain other late varieties are secured 

 without difficulty. No doubt climatic conditions have some- 

 thing to do with this but there is every reason to believe that 

 Rhizoctonia contributes its share in bringing about these unde- 

 sirable results the same as it did at Highmoor Farm, which is 

 located in the same section. 



That there is considerable difference in the resistance of dif- 

 ferent varieties of potatoes to the disease and possibly a differ- 

 ence in the resistance of different strains of the same variety is 

 indicated by our somewhat limited observations upon this phase 

 of the subject. Just what varieties are the most susceptible 

 and what are the most resistant remain to be determined. That 

 soil conditions are important factors with reference to the 

 virulence of the attacks of the fungus seems probable but just 

 what these conditions are is also unknown. 



Preventive Measures. 



The main object of the present publication is to prove that 

 Rhizoctonia is a real, though previously largely unrecognized, 

 cause of potato disease in the East, that at times with certain 

 varieties and under certain soil conditions it may become of 

 considerable economic importance, and to point out the promi- 

 nent characteristics by which it may be recognized. While 

 field and greenhouse experiments are being conducted along the 

 line of preventive measures we have secured no results which 

 add to the knowledge of this phase of the subject. Any advice 

 as to control measures then must be based upon previous work 

 or consist of recommendations of a more or less general or 

 empirical nature. 



The first thing to do is to determine by examination of ger- 

 minating and growing plants whether or not the fungus, which 

 is common in most potato soils, at least where potatoes have 

 been grown for any length of time, actually causes any material 

 injury to the varieties grown, under the soil conditions which 

 exist. If not it may be ignored unless one is growing seed pota- 

 toes for a trade which requires seed free from the fungus. If 

 the latter is the case or trouble is experienced from the disease, 



