298 Journal of Agricultural Research voj. xxvni. No. 4 
Titus, by H. B. Shaw and by the Office of Sugjhr-Beet Investigations, Bureau of 
Plant Industry, United States Department of Agriculture. 
Shaw (13) confirmed Ball’s findings regarding the occurrence of curly-top in 
sugar beets as a result of infestation by beet leafhoppers. He caged aphids, red 
spiders, thrips and beet leafhoppers on sugar beets and found that curly-top 
developed only in the beets on which the beet leafhoppers were caged. Shaw 
also reported that, even though no symptoms of the disease were visible when the 
beets were harvested the preceding fall, curly-top disease developed during the 
second season in beets planted for seed production, and that the symptoms of the 
disease were to be found primarily upon the young or growing leaves. 
Bunzel (7) reported a high oxidase content in the tissues of diseased beets, 
recalling the high oxidase content reported in earlier experiments on tobacco, 
mosaic. 
Smith and Boncquet (16) reported that exposure of beets foi; five minutes to 
infestation by leafhoppers was sufficient to cause the symptoms of curly-top to 
develop, although two weeks or more might be necessary before the symptom 
would be obvious. They reported a bacillus as associated with the disease. 
Boncquet and Hartung (6) reported beet leafhoppers not necessarily able to. 
cause the disease while, if such leafhoppers were first fed on, diseased beets and 
then allowed to feed on healthy beets curly-top would then develop. 
Smith and Boncquet (15) reported the finding of bacteria in the diseased beets and 
confirmed the report of Boncquet and Hartung of the apparent inability of the 
leaf hopper to transmit curly-top unless it had previously fed upon diseased plants. 
Ball (4) urged the use of the name “curly-leaf ” to clearly distinguish between 
the disease associated with leaf hopper attack and any disease having symptoms, 
in any way similar. He reviewed the status of curly-top or “ curly-leaf,” especially 
emphasizing the geographical relation of the breeding areas of the beet leaf hopper 
to the areas in which severe outbreaks had occurred. He also emphasized the 
periodicity of migrations from breeding areas and suggested the probability that 
epidemics of curly-leaf could be predicted through the recognition of the period¬ 
icity of the flights of the insect. Commenting on the finding by Boncquet and' 
Hartung that the insects were apparently unable to carry the disease unless they 
were fed upon diseased plants, he suggested the probability that some wild; 
plant was acting as carrier of the disease. 
Boncquet and Stahl (6) reported the occurrence of the curly-top infection in 
native vegetation. 
Stahl and Carsner (17) reported that recently emerged beet leafhoppers, 
lifted from the plant before feeding were not carriers of curly-top, but became* 
carriers of the disease when fed on diseased beets. 
Severin (10) stated that the insects caught on wild vegetation produced the 
disease in beets in some cases while in other cases they did not. He listed wild 
plants from which the leafhoppers were reared and from which these insects- 
transmitted curly-top to sugar beets. 
Carsner (8) reported fourteen species of plants representing eight families as 
susceptible to curly-top. 
Severin (11) demonstrated that after a nonviruliferous insect has fed on a 
diseased plant an incubation period for at least a few hours must elapse before- 
this insect can transmit the virus. 
Stahl and Carsner (18) reported that when an insect is once infected the in¬ 
fection is apparently permanent. 
The appearance of sugar beets affected with curly-top in the different stages 
of the disease might well be more adequately described, but for the purpose of 
this paper brief mention of some of the conspicuous symptoms will suffice. 
When a plant is infected the mature leaves remain normal in appearance, the 
vein swellings and curling of the leaves appearing on only the new growth. 
There is no conspicuous color change in the early stages of the disease (PI. 1). 
In the later stages the older leaves which were mature at the time of infection 
