WALNUT APHIDES IN CALIFORNIA. 
43 
ferred 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 winch 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 
2 
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 
Commercial tobacco extract No. 2 (1-1,500) 
.008 
2 per cent distillate-oil emulsion (homemade) and com- 
.0098 
July 31,1912 
do 
.0067 
2 per cent distillate-oil emulsion (commercial) and com- 
.0127 
Whale-oil soap (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° Baume). 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 
