THE BEET-SUGAR INDUSTRY IN 1920. 47 
way with a so-called leaf hopper, 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, usually in midsummer. Sometimes they destroy the plants 
before they are harvested, causing a serious loss to the grower. In 
I 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 fayors 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 
