16 Department Circular 329, U. S. Dept. of Agriculture 



POTATO 



The necessity for field inspection and selection of seed potatoes 

 has been confirmed by investigations of the plant pathologists, who 

 have brought to light the importance of disease as a factor in the 

 deterioration of seed stocks. It has been found that " degeneration " 

 of potatoes can be attributed largely to the presence in the field of 

 various forms of the diseases known as mosaic, leaf-roll, and 

 spindling tuber. 



These so-called "degeneration" diseases of potato, if present in 

 seed stock, may cause reductions in yield ranging from 15 to TO 

 per cent or even more. During the growing period aphids spread 

 the diseases from infected to healthy plants, so that in a large field 



Fig. 8. — A stop on a potato tour in New York to study diseases found in seed-source 

 test plots. The well-planned tour has been a most effective agency for making 

 farmers acquainted with the nature of plant diseases, their importance, and 

 methods of control. 



it is practically impossible to eliminate them by rogueing out the 

 obviously diseased plants. Owing to the fact that tubers from in- 

 fected plants produce diseased progeny the following year, it is 

 evident that they should not be used for seed. It is somewhat diffi- 

 cult to avoid this, because, unlike such troubles as scab and rhizoc- 

 tonia, the ''degeneration'' diseases can be recognized only by exam- 

 ining the growing plant. 



From the extension point of view, the problem is twofold. It 

 is necessary (1) to create among growers of table stock a recognition 

 of what constitutes disease-free seed and impress them with the 

 desirability of planting such seed, and (2) to develop among growers 

 of seed stock methods of producing seed potatoes and bring such 

 methods into sufficiently general use to supply the demand created 

 by educational work among growers of table stock. 



