October, '21] serverix ,v others: beet leaf hopper 409 



beet leaflioppers which were killed in screen wire cages with old dust 

 preparations varied as follows: 



Kaolin, Lime, "Black Leaf 40" 6^o, killed 16%. 



Kaolin, Lime, "Black Leaf 40" 8%, killed 75%. 



Kaolin, Lime, "Black Leaf 40" 10%, killed 16%. 

 The dust mixture containing 10% "Black Leaf 40" was now applied 

 to one acre of beets isolated by alfalfa fields and the percentage of beet 

 leaflioppers that were killed was approxim.ately detennined. Another 

 acre of beets was used as a check or control at a distance of about 1000 feet 

 from, the dusted field. The nearest beet fields were about a m.ile away 

 from, the two experimental areas. Before dusting, three m.en estim.ated 

 the number of bugs present in different rows of beets in the two acres 

 during the early m^oming. It was found that there was an average of 

 6 adults to 100 feet of a row of beets. After applying the dust at the 

 rate of about 100 pounds to the acre, there was an average of 5 adults 

 to 100 feet of a row of beets. The inefficiency of the dust was due to the 

 fact that the lim.e was partly air-slaked and lost som.e of its active jDrop- 

 erties. Four days later another dust mixture containing freshly burnt 

 lim.e was applied to the sam.e acre of beets. Three days after dusting 

 there were 4 adults and 1 nymph in 030 feet of beets or a reduction of 84% 

 of the hoppers. In the acre used as a check, there were 6 adults and 

 9 nymphs to 100 feet of a row of beets. 



The percentage of leafhoppers which were killed in screen wire cages, 

 with the newly m.ade dust containing 10%; "Black Leaf 40" and aj^plied 

 with a dusting machine at the rate of about 100 pounds to the acre varied 



as f olloA^-s • 



Dead 7 hours. Dead 24 hours. Dead 48 hours. 



59% 84% 96% 



92% 95% 100% 



56% 72% 82% 



Average 69% 83.3% 92.6%, 



No conclusions can be drawn as to the value of dust mixtures as a 

 method of control for the beet leafhopper, due to the fact that the beets 

 were planted after the invasion into the cultivated area had occurred. 

 The s])ring brood flew into the beet fields near King City between April 

 25-30, 1921. The beet seed was planted on May 9 and germ.inatcd on 

 May 20 in the dusted and check acres. The first application of dust 

 was applied on June 20, and the second on June 24, after the hatching 

 of the second brood n^-mphs had occurred. It is evident, however, that 

 with a reduction of 84% of the hoppers in a dusted acre of beets, a 

 m-arked decrease in the percentage of curly leaf would occur in isolated 

 beet fields providing the dust is applied shorth' after the spring flight of 

 the adults into the cultivated area. 



