158 Maine Agricultural Experiment Station. 1920. 



symptoms before death. This transmission is not modified by 

 seed treatment. 



(5) Its infectiousness has been proved by means of graft- 

 ing and of inoculations with juice from diseased plants. 



(6) Aphids, or plant lice, have been shown to be impor- 

 tant agents for natural transmission of mosaic from one potato 

 plant to another. 



(7) Transmission has been attempted by means of flea 

 beetles, Colorado potato beetles (or "potato bugs"), seed-cut- 

 ting knives, soil, and contact of seed pieces, leaves, stems, and 

 roots, but has not yet been demonstrated with any of these 

 agents. 



(8) The effects of the spread of potato mosaic to healthy 

 plants apparently cannot be avoided by the selection of hills or 

 tubers or by discarding parts of the seed tubers, unless plant 

 lice are controlled. 



(9) The relation between this spread and differences be- 

 tween localities, varieties, fertilizers, and spray methods are be- 

 ing studied but have not been fully determined. 



(10) Such spread has been reduced by roguing seed plots, 

 that is, by removing mosaic hills as fast as they appear, and 

 absolutely prevented by thorough control of certain kinds of 

 insects. 



(11) Potato mosaic is difficult to control but it is now pos- 

 sible to recommend measures that promise to be helpful. 



Introduction. 



The disease of Irish potatoes known as mosaic has been 

 Itnown for a long time in Europe, according to Quanjer 2 , al- 

 though without the present name always being applied or the true 

 nature of the disease well understood. It was found to be preva- 

 lent in the potato fields of Aroostook County, Maine, in 1912 3 . 

 In 19 1 7 and 19 18 it was reported from twenty-one states 4 , includ- 



2 Quanjer, H. M. The mosaic disease of the Solanaceae, its relation 

 to the phloem-necrosis, and its effect upon potato culture. Phytopath. 

 10:35-47. Figs. 1-14. 1920. 



3 Orton, W. A. Potato wilt, leaf-roll, and related diseases. U. S. 

 Dept. Agr. Bui. 64. 48 p. 16 pi. 1914. 



4 U. S. Department of Agriculture. Bureau of Plant Industry. Plant 

 Disease Survey. Plant Disease Bulletin, Vol. [1]-2:1917-1918. 



