FEDERAL. HORTICULTUEAL, BOARD. 627 



The infestation as now determined in southwestern and western 

 Pennsylvania includes points in Cambria, Olearlield, Center, Arm- 

 strong, and Huntingdon counties. The work of this year, therefore, 

 has materially extended the infestation in this part of the State. 

 The infested area in eastern Pennsylvania remains substantially the 

 same as reported last year. 



The intensive search made in the coal mining sections of northern 

 and southern West Virginia did not result in the discovery of any new 

 areas of infestation in that State. The old area in the immediate 

 vicinity of Thomas, W. Va., was, however, slightly extended by the 

 discovery of the disease in two neighboring villages. 



The wart disease was discovered in Maryland in eastern Allegany 

 County in three villages in the neighborhood of Frostburg. But a 

 single infested garden was found in each village, but on account of the 

 lateness of the season a full determination of the infestation could 

 not be made. Furthermore, the principal potato gro^^'n in the district 

 is the Cobbler, which is immune to the disease. There is reason to 

 believe therefore that the disease may be more extensively present 

 in this section than is now known. Its discovery in Allegany 

 County, Md., is of special importance since the growing of seed pota- 

 toes is becoming a considerable undertaking in that immediate 

 locality. 



Unlike the infestation in eastern Pennsylvania, the infested locali- 

 ties in the soft coal regions in western Pennsylvania, Maryland, and 

 West Virginia are apparently scattered, the disease occurring in single 

 gardens or in a small number of gardens in each village. 



RESEARCH WORK ON POTATO WART. 



Determination of immune varieties of potatoes. — -The research 

 work in connection with the potato wart, begun in 1919, has been 

 continued but on a more extensive scale in cooperation with the 

 state colleges and departments of agriculture of Pennsylvania and 

 West Virginia. Up to date some 78 named American varieties of 

 potatoes have been tested and of these 27 have been found to be 

 mimune to the wart disease. In addition, a great many seedlings 

 have been tested and also a considerable number of foreign varieties, 

 English, Scotch, and German, many of which also appear to be immune 

 varieties. It is worthy of note that all the varieties found to be 

 immune in the tests of 1919 have retained their immunity through 

 the second year of testing. Their reaction to the wart disease has 

 also been the same in Pennsylvania and West Virginia. 



Some of the imported innnune varieties show considerable promise 

 for general distribution in this country and stocks of these will be 

 increased next year. The number of knoMTi American varieties 

 immune to the wart disease now covers the range from early to late 

 potatoes and includes several of the best commercial varieties. These 

 stocks likewise will be much increased in 1921. 



Disinfection of soil. — Considerable progress has been made in 

 the determination of the feasibility of disinfecting soil known to be 

 invaded by the disease. Soil which was thus disinfected by steam 

 and l>y chemicals and other means in 1919 was planted to potatoes 

 susceptible to the disease this season and the results, while not 

 thoroughly effective in controlling the disease, have been very promis- 



