THE BEET-SUGAR INDUSTRY IN 1920. 47 



way with a so-called leafhopper, which appears to be only a carrier 

 and not the real cause of this disease. A further study of curly-top 

 has been undertaken by the Office of Sugar-Plant Investigations in 

 cooperation with the Bureau of Entomology, in the hope of being able 

 to determine the exact cause of the disease, and especially for the 

 purpose of finding some practical means of control. Curly-top does 

 not usually occur to any serious extent two years in succession in 

 the same field, although there are some exceptions to this rule. Fre- 

 quently it will occur over a given area, destroying or stunting to a 

 worthless size practically all of the beets for a season and then 

 almost entirely disappear, so that the next year beets of good tonnage 

 and quality may be grown on the same fields. It is possible that 

 there are other carriers besides the leafhopper and that certain soil 

 and climatic conditions favor the development of this disease. The 

 real cause, however, is undoubtedly organic in nature ; it is probably 

 either an organism or an organic compound ; but until this cause is 

 known little progress can be made in finding a reliable method of 

 control. Curly-top has played an important part in closing at least 

 two beet-sugar mills and has caused losses of hundreds of thousands 

 of dollars in other localities. 



Root-rot.- — There are several destructive diseases of the sugar beet 

 known as root-rot. One of these is due to a fungus called Phoma 

 and another is due to a fungus known as Rhizoctonia. Other root 

 rots less extensive or little known are due to other fungi or to 

 bacteria. The Phoma, rot seems to be more prevalent and more 

 destructive than the Rhizoctonia. These fungi attack the beets in 

 the field, usualty in midsummer. Sometimes they destroy the plants 

 before they are harvested, causing a serious loss to the grower. In 

 other cases they make only a slight attack on the beet in the field, 

 but develop more or less rapidly when the beet has been placed in 

 storage, either for sugar-making purposes or for seed production. 

 The Phoma fungus causes more loss to stored roots than any other 

 agency, especially if the temperature favors the development of the 

 fungus. These diseases are found in all parts of the sugar-beet 

 area in this country and in Europe. The most successful means 

 of combating the root-rot of beets in the field is crop rotation,; 

 and if it does not get started in the field there is little danger 

 of its developing in storage. 



Leaf-spot. — Two fungi which produce spots on the leaves of beets 

 are more or less general throughout the United States and Europe. 

 One of these is known as Cercospora and the other as Phoma ; the 

 latter is the same fungus that produces the root-rot. When the 

 spores of either of these fungi fall upon the beet leaves and the con- 

 ditions are favorable the fungus growth attacks the tissue of the 

 leaf, producing distinct and characteristic spots. The Cercospora 



