366 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 15 



In checking up the percentage of blight in a field, two rows of 50 beets 

 were counted, and the average percentage of curly leaf was computed. 

 Curly leaf was determined by examining the youngest or innermost leaf 

 of a beet for the earliest visible s\Tnptom; namely, the transparent 

 network of minute veins. 



The determination of the niunber of beet leaf hoppers to 100 feet of 

 beet row is a difficult and tedious task. Trial after trial by sweeping 

 with an insect-net proved that this method of ascertaining the number 

 of insects in a beet field was inaccurate. The method which we employ- 

 ed was to disturb the foliage with the hand and carefully examine each 

 beet and surrounding soil for leafhoppers, while the observer crawled 

 along the row of beets on his hands and knees. Months of this experi- 

 ence makes one very adept and the possible error is reduced to a mini- 

 mum. Time after time observers have checked the results of each other 

 and the counts of the number of hoppers were so nearly the same, that 

 it is felt that the data thus obtained is reliable. 



In the Salinas Valley, where this work has been carried on systemat- 

 ically weather conditions are an important factor in ascertaining the 

 number of insects. Early in the morning, when it is cool and still 

 quiet, the adults in the beet fields are sluggish and easy to count. In 

 the Salinas Valjey a daily wind blows from about 10 a.m. until evening. 

 When this wind prevails, the hoppers are difficult to find and the work 

 for the day must cease if accurate results are to be recorded. During 

 cloudy, cool mornings the determinations are very accurate; on warm, 

 sunshiny mornings, the activity of the leafhopppers makes observation 

 more difficult and less accurate. 



During 1920, the number of adults in the beet fields of the Salinas 

 Valley remained almost constant from the time that the invasion of the 

 pest occurred in early May until the second brood adults m^ade their 

 appearance during the last week in June. Nymphs began to appear in 

 early June and increased as the month progressed. The same condition 

 with slight modifications was found to be true in the present season of 

 1921. 



The size of the beet at the time that the leafhoppers appear in consid- 

 erable nvimbers in the fields and the relative number of hoppers present 

 have a direct bearing on the tonnage harvested. At King City three 

 beet fields on which data was kept during 1920, showed the effect of the 

 time of planting. One tract planted about April 1, was being thinned 

 about the time that the spring brood adults flew into the beet fields 

 during the early part of Ma}^ By June 26, these beets were all blighted, 



