46 BULLETIN 721, U. S. DEPAETMENT OF AGRICULTURE. 



seen in the eastern portion of the sugar-beet area or in any of the 

 beet fields of foreign countries. It has appeared in practically all 

 States west of Minnesota and Iowa where sugar beets are grown 

 commercially, although it has not been seen in all of the sugar-beet 

 areas of the West. It is not due to unfavorable climatic or soil 

 conditions, nor is it due to the kind or quality of seed used. It is 

 connected in some way with a so-called leafhopper, which appears 

 to be only a carrier and not the real cause of the disease. A further 

 study of curly-top is being 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 excep- 

 tions to this rule. Frequently it will occur over a given area, de- 

 stroying 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 elosing 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 Khizoctonia. Other root- 

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

 teria. The Phoma rot seems to be more prevalent and more destruc- 

 tive than the Ehizoctonia. 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 other 

 cases thej^ 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-s'pot. — There are two fungi that produce spots on the leaves 

 of beets which are more or less general throughout the United States 



