182 Maine Agricultural Experiment Station. 1920. 



In 1918, stock unrogtied and partly mosaic in 191 7 was 

 divided into two parts, one unsorted and the other with tubers 

 of 2 ounces and less in weight discarded. The percentage of 

 mosaic differed only two-thirds of one per cent, being about 45 

 per cent for each. The plots observed covered about one-fifth 

 acre each. 



SELECTION OF SEED PIECES. 



Tuber units, or groups of plants each from a single tuber, 

 are often mixed regarding mosaic, that is, partly diseased and 

 partly healthy. In experiments conducted in 1918 and 1919 with 

 such tuber units, there was a preponderance of mosaic in bud- 

 end hills. This, however, is of no value regarding the problem 

 of control because of the small percentage of tubers that will 

 produce both healthy and diseased plants. It is far more im- 

 portant to take measures which will eliminate all tubers that are 

 either partly or wholly mosaic. 



REMOVAL OF DISEASED PLANTS. 



Since the selection of hills, tubers, or seed pieces seems, with 

 our present knowledge, to be of no great value in securing or 

 maintaining healthy potato stocks, contrary to experience with 

 certain other potato diseases 17 , the results secured by removing 

 diseased hills from seed plots are of interest. This method in- 

 cludes several careful inspections for mosaic plants, their re- 

 moval as soon as found, and of course harvesting and storing 

 the crop separately from all diseased stock. If only one inspec- 

 tion is made it should not be made until all of the plants from 

 diseased tubers have become large enough to show mosaic. In 

 1919 in all-mosaic stocks only 6j per cent were mottled in Green 

 Mountains and 89 per cent in Bliss Triumphs by July 9. In 

 the early part of that season the unusually high temperatures 

 probably retarded the development of mottling directly and on 

 the other hand hastened it indirectly by accelerating the develop- 

 ment of the plants. All plants in these lots were plainly mosaic 

 by the last of July. A single inspection made late enough to 



"See Me. Agri. Exper. Sta. Miscel. Publ. 535, on "How to Control 

 Potato Enemies." 



