24 a EXPERIMENT STATION. [Jan. 



the average for the State was above 20 per cent of diseased 

 plants. As high as 80 per cent was noted. The estimated 

 reduction of yield due to mosaic is from 10 to 80 per cent. 

 Leaf roll was more frequently observed on Irish Cobblers. 

 These and certain other so-called degeneration diseases are 

 communicable through the tubers. They are, as a rule, more 

 abundant where home-grown ''seed," or "seed" from one to 

 several -generations from the north, are used. While northern- 

 grown potatoes are by no means free from these diseases, it is 

 apparent that climatic conditions in Massachusetts tend to 

 increase them. Except in the higher regions of the State, 

 progressive increase of these diseases and consequent degenera- 

 tion invariably attend attempts to grow potatoes from the 

 same stock year after year. As the production of suitable 

 seed potatoes in our higher altitudes is inadequate to the 

 demands of the entire State, it is evident that if the potato 

 yield of the State is to be increased or even maintained growers 

 must depend largely on northern-grown ''seed." Only properly 

 inspected and certified "seed" should be accepted, because 

 many northern fields are badly infected with tuber-communi- 

 cated diseases. A movement has been initiated through the 

 extension service, to promote and encourage the practice of 

 planting only good "seed" potatoes. General adoption of this 

 practice would result in much benefit to- the potato growers, 

 and would increase the State's total production without in- 

 creasing the area devoted to the crop. An effort also will be 

 made to have non-susceptible varieties substituted for the 

 Green Mountain type. 



The more common potato diseases were by no means entirely 

 absent last season, although the troubles above discussed were 

 responsible for a large part of the losses previous to harvesting 

 the crop. In July early blight was rather severe in some fields, 

 but the ravages of this disease were checked by the drought. 

 Late blight was present in many fields, but the outbreak was 

 light and little damage in the field resulted. However, heavy 

 rainfall in September, before the bulk of the crop was harvested 

 and stored, gave the fungus of this disease a start in the tubers, 

 and the result has been heavy losses in storage. 



The wet weather of September also proved detrimental to 



