222 The Potato 



Department of Agriculture, Washington, D. C, has 

 reported certain varieties that have shown considerable 

 resistance to both early and late blight. These are 

 Apollo, Sophia, Professor Wohltman and Max Eyth. 

 They are all foreign varieties and under conditions of 

 climate and soil in the United States they succeed very 

 poorly, being light yielders and rather poor in quality. 

 Stuart remarks that it would seem as if high disease- 

 resistance of the vine was correlated with low yield and 

 undesirable tubers. He found no varieties tested to have 

 strongly marked scab-resistant qualities when grown in 

 soil well infested with the scab organisms. He believes 

 that the value of disease-resistant varieties is problem- 

 atical, but that the plant-breeder, by mating them with 

 the most desirable commercial American types, may 

 develop commercial types of resistant varieties. 



Summary 



It may be well to summarize control measures in the 

 following way : — 



What selection does. — It aids in eliminating curly- 

 dwarf, leaf-roll, mosaic, the various wilts, black-leg and 

 other diseases showing on the vines and also transmitted 

 by the tuber. It eliminates low-yielding hills. It elimi- 

 nates impurities in a variety. 



What seed treatment and rotation do. — They reduce in- 

 jury from rhizoctoniose, scabs and black-leg. They 

 increase the stand of potatoes in the field. They give 

 clean tubers. 



]Vhat spraying does. — It prevents early and late 

 blight. It prevents the blight rot. It reduces injury 

 from tip-burn. It repels flea-beetles. It kills the bugs. 



