318 
Journal of Agricultural Research 
Vol. XXVIII, No. 4 
SUMMARY 
Curly-top disease of beets is characterized by a dwarfing of the whole plant, 
curling of the leaves, and irregular swelling of the veins on the under sides of the 
affected leaves. Marked phloem necrosis is produced throughout and shows as 
more or less conspicuous dark rings in cross sections of the root. 
The disease is known to occur in only the semiarid regions of the western part 
of North America. 
Curly-top is the cause of greater losses than any other sugar beet disease in 
this country. Very great damage to beets results when they are grown as an 
annual crop and when grown for seed production. 
The exact nature of the cause of the disease is unknown, but the fact has been 
demonstrated that the virus can be transmitted by the beet leafhopper (Eutettix 
tenella Baker). No other means of transmission is known. The ability to 
produce the disease is not inherent in the leafhopper. There is some evidence 
that an interval of a few hours, an incubation period, must elapse after a nonvi- 
ruliferous leafhopper has fed on a diseased plant before it can effectively transmit 
the virus to a healthy plant. Ten or more insects are more likely to produce the 
disease in an inoculated plant than when the inoculation is made with one or two 
insects. In cases where the disease is produced there is no difference in the 
incubation period or severity of the effect between inoculation with single insects 
and those with ten insects. A viruliferous leafhopper may not produce the 
disease each time it feeds on a healthy plant, even though the periods of feeding 
be 24 or 48 hours or even longer. 
Tests in regard to the relation of light to infection indicate that plants kept 
in darkness during inoculation are more readily infected through the cotyledons 
than through the true leaves. 
Tests of the effect of heat on the disease indicate that the virus is not destroyed 
by temperatures lower than those at which the beet tissue is killed. 
Limited data suggest that the virus may be destroyed by desiccation. 
The virus is distributed through all parts of an affected plant. 
Limited data suggest evidence opposed to the claim that a specific bacterial 
organism is associated with curly-top. 
The incubation period of the disease varies usually from 7 to 14 days. As 
short an incubation period as 4 days has occasionally been noted. 
The incubation and development of the disease is retarded by low tempera¬ 
tures. 
Very young plants are more readily infected than are older plants. 
A wide range of species has been found susceptible to curly-top. 
The virus probably overwinters in susceptible wild annuals, in volunteer 
beets, and in the insect. 
No satisfactory control of the leafhopper by artificial or biological means has 
been discovered. Early planting usually avoids much of the injury. There is 
basis for belief that a resistant strain of beets may be developed. 
LITERATURE CITED 
(1) Ball, E. D. 
1906. the beet leaf-hopper (eutettix tenella). Utah Agr. Exp. 
Sta. Ann. Rpt. 16 (1904/05): 16. 
( 2 ) -. 
1907. the genus eutettix. Proc. Davenport [Iowa] Acad. Sci. 12: 
27-94, illus. 
(3) -. 
1909. THE LEAFHOPPERS OF THE SUGAR BEET AND THEIR RELATION TO 
the “curly-leaf” condition. U. S. Dept. Agr. Bur. Ent. 
Bui. 66: 33-52, illus. 
