WALNUT APHIDES IN CALIFORNIA. 



45 



The best results, therefore, were obtained by the lime-sulphur 

 wash. The greater efficiency of the 8 per cent crude-oil emulsion 

 over the 12 per cent crude oil used in experiment No. 1 is probably 

 due to the heavier grade of oil (22° Baume) used in the 8 per cent 

 experiment. The heavier oil remains longer on the trees and coats 

 the eggs of the aphides more satisfactorily than the oil of fighter 

 grade. As may be seen from Table XVI both the 8 per cent crude- 

 oil emulsion and " Yel-ros," 1 to 25, gave good results, but " Yel-ros," 

 1 to 40, was quite ineffective. Table XVI is a summary of experiments 

 against the winter eggs: 



Table XVI. — Summary of experiments on the winter eggs, Walnut Creek and Santa 



Rosa, Cal, 1913. 



Character of spray. 



Date of ap- 

 plication. 



Number 

 of trees 

 sprayed. 



Date of ex- 

 amination. 



Plant 

 lice 



present 



(check — 



100). 



Cost per 

 diluted 

 gallon. 



Crude-oil (27° Baum6) emulsion, 12 per cent. 



Commercial lime-sulphur, 1 to 10 



Crude-oil (22° Baum6) emulsion, 8 per cent. . 



Commercial lime-sulphur, 1 to 8 



"Yel-ros," 1 to 25 



"Yel-ros, " 1 to 40 



Feb. 25... 



Mar. 5 



Apr. 9-11. 



do... 



do... 



do... 



Apr. 5, 15 



do.. 



May 27.. 



do.. 



....do.. 

 ....do.. 



Per cent. 

 72.4 

 .0 

 10.6 

 1.9 

 13.4 

 93.2 



3.01 

 .02 

 .0073 

 .025 

 .028 

 .0175 



It is in a measure unfortunate that the homemade 1-2-1 lime- 

 sulphur spray was not tried. This is considerably cheaper than the 

 commercial article, but there is no reason to suppose that the winter 

 formula of the homemade lime-sulphur would not prove quite effective 

 judging by the results obtained with commercial lime-sulphur. 



In recommending winter sprays for the plant lice infesting walnut 

 trees the writer must accord the preference to lime-sulphur, 1-8 to 

 1-11, while good work may be expected from crude-oil emulsion, 8 to 

 12 per cent, using the heavier grades of oil (not lighter than 24° 

 Baume), and from "Yel-ros," 1-25. The oil emulsion (homemade) is 

 the cheapest winter spray, although there is little difference between its 

 cost and that of the homemade lime-sulphur wash, winter formula. 



In applying the spray for the aphis eggs the wash should be directed 

 so as to cover completely every part of the twigs and limbs. Late 

 spraying, i. e., making the application just before the buds are begin- 

 ning to swell, is preferable to spraying earlier, especially if crude-oil 

 emulsion is used, as the oil does its best work soon after it is applied 

 and the plant lice at hatching time are more easily destroyed by it. 



In concluding the section on artificial control the author would like 

 to express his thanks to Mr. Frank Leib, San Jose, Cal., and Messrs. 

 George Whitman and E. I. Hutchinson, Concord, Cal., for their help and 

 cooperation in the carrying out of field experiments on their orchards, 

 and also to Balfour, Guthrie & Co., San Francisco, Cal., by whose 

 courtesy the Santa Rosa experiments were made possible, they having 

 made the spray applications under the author's supervision. 



