198 The Sugar-Beet in America 
swarms fly from their breeding grounds on wild plants for 
long distances over mountain chains and other barriers. 
Sometimes there will be only one flight into a partic- 
ular region; if so, beets coming up later will not be 
infested. 
“Leafhoppers taken from wild plants do not transmit 
the disease until they feed on diseased beets. Three hours 
on a beet rendered them pathogenic, but they could not 
transmit until after an incubation period of one or two 
days. It is probable that some wild plant carries the 
disease and leafhoppers coming from this plant are able 
to transmit it to the beets. 
“A large number of leafhoppers, early attack, hot 
weather, and clean cultivation are favorable to the curly- 
leaf development. The converse of these factors, together 
with frequent cultivation, early irrigation, and shade or 
weeds, are unfavorable. Seed growing is doubly hazard- 
ous in curly-leaf areas. 
“Loss from curly-leaf may be largely prevented by 
avoiding dangerous areas, by planting small acreages 
in a ‘blight cycle,’ by controlling the time of planting, 
by not thinning just as the leafhoppers appear, and by 
knowledge of conditions on breeding grounds. Para- 
sites doubtless assist somewhat in controlling the leaf- 
hopper, but to be at all effective ‘should be introduced 
into the permanent breeding grounds.” 
DISEASE INJURY 
The losses due to beet diseases have not been great in 
America, probably because beets have been grown here 
