REPORT OF THE SOCIETY 49 



EFFICIENCY FACTORS IN POTATO SPRAYING 



Dr. W. H. Rankin, Cornell University 



Spraying late varieties of potatoes five to seven times every year with bor- 

 deaux mixture largely eliminates many of the factors which cause a fluctuation in 

 yield. Since spraying thus furnishes a means of making a much larger profit on 

 potatoes, no potato grower can afford to neglect this rather simple but sometimes 

 distasteful practice in this section of Canada and adjacent United States. 



The accuracy of these assertions is no doubt already well recognized by the 

 majority of those present. \\'here proof is desired, however, we need only refer 

 to the experiments conducted for a period of twenty consecutive years at the 

 Vermont Agricultural Experiment Station, and the ten year experiment in New 

 York State. In the Vermont experiments the yield was increased 116 to 224 

 bushels to the acre by spraying in years when late blight was destructive.^ Even 

 in years when there was no late blight, an average increase of 66 bushels to the 

 acre was realized. In the New York ten year experiment an average increase of 

 45 to 97 bushels to the acre was obtained. This increase is realized not only by 

 the expert, but by the average grower as well. One hundred and fourteen 

 New York farmers reporting definite figures on costs and results showed an 

 average increase in yield of 36 bushels to the acre. Two hundred and four farmers 

 reporting only on yield showed an average increase of 54 bushels to the acre.^ 

 These results mean that the farmer received on the average every year in money 

 returns over three times the total costs of the spraying. 



Despite the decided advantages in favor of every potato grower spraying 

 every year, many do not spray. It was in view of this fact, and also because 

 there are many factors in potato spraying which need emphasis that I have 

 have chosen this subject tonight. Before proceeding with the discussion of some 

 efficiency factors in potato spraying, it is necessary that we call to mind certain 

 facts regarding the troubles which spraying helps to control. 



No matter how free the crop may be from the many diseases which are 

 carried over from year to year in the tubers, the late potato varieties in this 

 climate are subject to injury by early blight, late blight, tip-burn, the Colorado 

 beetle and flea beetle. Considerable effort has been expended to select and breed 

 varieties resistant to early and late blight. These measures have been largely 

 without successful results, although many varieties of commercial importance 

 show varying degrees of resistance. The exact combination of weather condi- 

 tions in July and August determines largely the destructiveness of early blight, 

 tip-burn and late blight. It is pertinent to observe here that the seasonal con- 



