WALNUT APHIDES IN CALIFORNIA. 



43 



f erred to one of the Clipper type, as the former will diffuse the spray- 

 better over the leaf surface. Such a driving-spray nozzle as that 

 devised by the Massachusetts Agricultural College is desirable for 

 spraying trees of large size. If there are unsprayed walnut trees 

 in the vicinity it may be necessary to make a second application 

 some two or three weeks later, as plant lice are apt to have migrated 

 from these to the sprayed trees. 



On account of the extended period over which the sexual forms are 

 produced, fall spraying for these forms, unless repeated again and 

 again, wiU be of little value. 



It should be borne in mind that the number of "lice" hatching in 

 the spring from the winter eggs varies considerably year by year in a 

 given locality or orchard and also that the hatching time of these 

 "lice" is regulated by the sap flow in that particular tree upon which 

 the eggs happened to be placed. The hatching of the winter eggs 

 is not regulated by temperature conditions. Hence the stage in the 

 seasonal development of the aphidids corresponds to the stage in 

 development of that particular tree on which the stem-mother lice 

 were produced, leaving out of consideration the possibility of mi- 

 grants arriving from other trees. This point is of importance when 

 it is considered that the different varieties of cultivated walnuts put 

 out their leaves and produce their nuts at different times and that 

 these functions are performed by individual varieties at different 

 times dependent on locality and seasonal meteorological conditions. 



Table XIV summarizes the control experiments made for spring 

 and summer treatment. 



Table XIV. — Summary of spring and summer spraying experiments against walnut 

 aphides, San Jose and Walnut Creek, Cal., 1911, 1912, and 1913. 



Character of spray. 



Date of appli- 

 cation. 



Number 



trees 

 sprayed. 



Result of 

 spray; per 



cent of 

 plant lice 



killed. 



Cost per 

 diluted 

 gallon. 



Commercial lime-sulphur, 1-50 and commercial tobacco 

 extract No. 2 (1-1,500) 



July 1, 1911 



July 3, 1911 



May 21,1912 



do 



1 



10 



10 

 6 



6 

 12 



95 



95 

 40 



98 

 74 



85 

 55.6 



$0,012 



3 per cent distillate-oil emulsion (homemade) and com- 

 mercial tobacco extract No. 2 (1-2,000) 



.0088 





.008 



2 per cent distillate-oil emulsion (homemade) and com- 

 mercial tobacco extract No. 2 (1-1,500) '. 



.0098 





July 31,1912 

 do 



.0067 



2 per cent distillate-oil emulsion (commercial) and com- 



.0127 



Whale-oil aoap (homemade), 1 pound to 5 gallons water.. 



May 10,1913 



.004 



WINTER TREATMENT. 



Experiment No. 1 . — Crude-oil emulsion, 12 per cent (crude oil, 27° Baum£). Orchard 

 of Mr. George Whitman, Concord, Cal. A block of 31 European walnut trees of moder- 

 ate size were sprayed February 25, 1913, under a pressure of from 150 to 175 pounds. 

 Three gallons of spray were applied to each tree and ' ' Friend" nozzles used. The trees 

 were well drenched. Examination made April 5, 1913, showed that trees were start- 

 ing to leaf. Most of the leaves were as yet tightly closed, but the basal leaves of many 



