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JOURNAL OF ECONOMIC ENTOMOLOGY 
[Vol. 17 
Periodical Outbreaks 
According to Ball (1) the periodical outbreaks of the beet leafhopper 
west of the Rocky Mountains occurred during 1899-1900, 1905, either 
1914 or 1915, and east of the Rockies in 1903 and 1908. 
In California the most reliable records of the outbreaks of curly leaf 
date back to 1899 at King City in the Salinas Valley. The periodicity of 
the beet leafhopper and the interval between outbreaks may be shown as 
follows: 
1899-1900, 1905, 1913-1914, 1918-1919-1920-1921-1922 
4 7 3 years. 
It is evident that, with the exception of 1905, the outbreaks of the 
beet leafhopper occurred twice in two successive years and once in five 
consecutive years. An examination of the number of acres planted, the 
acreage abandoned, and the tonnages harvested indicates that when 
blight occurs in two successive years, the drop in tonnage due to the 
disease is greater in the second year. During the years 1918 to 1922, 
curly leaf caused greater losses during 1919 and 1921, than in 1918, 
1920 and 1922, when the acres abandoned are taken into consideration. 
The largest losses were sustained during the second year in 1919. 
Factors Favorable for Increase of Beet Leafhoppers 
What are the factors associated with the severe outbreak of the beet 
leafhopper during the second year? On September 11 to 13, 1918, heavy 
rains fell in the San Joaquin and Salinas Valleys, germinating the seeds of 
the pasture vegetation on the plains and foothills, and a new growth of 
weeds developed in the cultivated areas. During the autumn the salt- 
bushes and other favorable host plants of the leafhopper normally be¬ 
come dry and the nymphs which hatched from eggs deposited in the fall 
by the females of the summer broods now found an abundance of food in 
this new growth of vegetation in the cultivated territories. These 
nymphs acquired the winged stage subsequent to October and November 
after the return flight of the dark winter adults to the plains and foot¬ 
hills. During the winter these stragglers which remained behind in the 
cultivated districts congregated on the very earliest planted beets in the 
northern part of the San Joaquin Valley and one-half of the 1919 crop 
showed curly leaf symptoms before the enormous numbers of pale green 
leafhoppers of the spring brood flew from the plains and foothills into 
the cultivated regions during April. According to Mr. W. W. Thomas, 
over one-half of the beet crop was blighted at King City (Ranch 3) by 
