434 OHIO EXPERIMENT STATION: BULLETIN 214 
In Europe, especially in Germany, in 1907 and possibly in the seasons since 
much complaint has been made of a similar disease to that described by 
Stewart as a leaf-roll disease (Blattrollkrankheit). In the European disease as 
well as in the stem bllght of potatoes described by Stewart in New York (See 
Bulls. 101 and 138) and in our present fusarium blight, the leaves of the affected 
plants lose color and roll upward from the border. With this occurs a general 
loss of green in the plants. Orton, who has made a general study of the disease 
throughout the country, regards the fusarium of dry-rot as the causal organism, 
and finds very serious checks upon potaio growing have resulted in San Joaquin 
county, California, upon so-called tule ‘lands where continuous cropping in 
potatoes has been more or less practiced. The evidence is conclusive that we 
have in the dry-rot organism a blight organism of the potato plant which is at 
the same time a soil infesting as well as a seed tuber infecting fungus. In 
addition to this, incomplete observations support the idea that some spread of the 
organism takes place as with other fungus parasites in the field. In the matter of 
preventive measures and remedies, the first consideration should be given to seed 
tubers. These should be of such source and character as are clear from infection, 
‘This infection may easily be determined by cutting across the stem end of the 
tubers. Evidently cellar stored seed is dangerous during this period of epidemic. 
In the matter of spray prevention we have evidence in a cooperative test in Portage 
County, that the spray holds back the advance of the development. Upon dupli- 
cate plots where strong Bordeaux mixture was used, the gain was at the rate of 
13 bushels per acre above any other sprayed plots; and 9 bushels per acre above 
the checks. These plots remained green longer than any of the others and show 
a decided reaction to the copper fungicide. From the behavior of certain hills 
in the various fields whose tops remained green in spite of the general infection, 
breeding for blight resistance should give decisive results. 
Late Blight or Rot of the Potato (Phytophthora infestans De By) called in Europe 
“the potato disease’’ is caused by a downy mildew fungus. This mildew spots 
the leaves, producing a downy, felt-like covering in spots on the under side of 
the leaves of infested plants. This causes prompt dying with wet-rot conditions 
of the leaves and the tubers are rapidly destroyed with wet-rot appearances. The 
potato Phytophthora is a disease which like its host plant is accustomed to 
somewhat cooler conditions of climate than usually prevail in Ohio. However, 
in the years 1904 to 1907 all the summer months were several degrees below the 
normal; this resulted in continuous out-breaks of the blight or rot, culminating 
in 1906-7. In 1908 under warmer or drier conditions while the fungus was found 
at Wooster it did not inflict damage here or elsewhere in the state. It is unlikely 
to be injurious in Ohio, except in seasons cooler and more moist than normal. 
(See table of seasons page 354). 
Spraying for late blight is entirely successful and should begin by the 20th of 
July, being repeated at intervals of two weeks and applications made at the rate 
of 100 gallons per acre on full grown vines. The duration of the spraying will 
depend upon the maturity of the plants, in the late crops reaching four or occas- 
ionally five sprayings. 
Rosette. The Rosette or Rhizoctonia disease often prevails in Ohio, especially 
where potatoes are grown on acid soils. This acid condition is evidently 
favorable to the fungus which attacks the stems of the young plants or even in 
early developments of the stems, these are often rotted off below the surface for the 
earth. In later developments the elongation of the plant axis is stopped and a 
rosette appearance is shown in the leaves. The disease survives by the red- 
