December, ’24] 
severin: beet leafhopper fluctuations 
641 
the overwintering brood before the spring generation invaded the beet 
fields. 
The writer (3) has published the fact that nymphs were also taken 
during November and December, 1918, on Red Stem Filaree (Erodium 
cicutarium ) growing on the foothills of the San Joaquin and Salinas 
Valleys. These nymphs hatched from eggs deposited in Red Stem 
Filaree by the summer brood females and not by the dark overwintering 
forms. 
The Weather Bureau reports for Stockton, situated in the northern 
part of The San Joaquin Valley, show that there were only five years in 
which the September rainfall was more than one inch during the past 74 
years, as follows: 1894—1.76; 1899—3.59; 1904—2.27; 1912—1.39; 
and 1918—3.68 inches. It is evident that heavy September rains fell 
during 1899, 1904 and 1918, and were followed in the next year by 
severe outbreaks of curly leaf. The year 1913 is the only exception in 
which a trace of rainfall recorded for September and October was followed 
by serious damage from curly leaf during the following year 1914, but 
September rains recorded for 1912 preceded the outbreak of blight in 
1913. In the Salinas Valley an abundance of rain fell at King City 
during the autumns of 1913 and 1918, preceding the serious outbreaks of 
curly leaf during 1914 and 1919. 
On the other hand, when no large amount of green vegetation is 
available in the cultivated areas during a dry autumn, the number of 
stragglers is greatly reduced and a low percentage of curly leaf occurs in 
early planted beet fields during the winter. During September, 1917, 
.14 inches of rain fell at Manteca, and 4 per cent of the early planted 
crop was affected with curly leaf in the northern part of the San Joaquin 
Valley before the pale green adults of the spring brood flew into the 
beet fields during April, 1918. Again in 1919, .49 inch of rain fell in 
September, and about one beet in a thousand showed the disease symp¬ 
toms before the pest invaded the beet fields during April, 1920. No 
rains fell during September, 1920, and an average of 5 per cent of the 
early planted beets were blighted before the spring dispersal of the first 
brood from the plains and foothills into the cultivated areas occurred in 
April, 1921. 
Although the dark winter brood adults which remained behind in the 
cultivated areas caused curly leaf in half of the crop of the earliest 
planted beets in 1919, nevertheless, the most serious factor associated 
with the severe outbreak of the disease is the enormous hordes of pale 
green leafhoppers which invaded the beet fields during April. Al- 
