WALNUT APHIDES IN CALIFORNIA. 41 
Commercial lime-sulphur, 1-50, combined with commercial tobacco extract No. 1, 
1-200, effective. 
Commercial lime sulphur, 1-70, combined with commercial tobacco extract No. 2, 
1-1,000, effective. 
Commercial lime-sulphur 1-45, combined with commercial tobacco extract No. 2, 
1-2,000, effective. 
It is noticeable that the weaker solutions of tobacco extracts were 
not effective alone, but when combined with distillate-oil emulsion or 
lime-sulphur proved quite satisfactory. Possibly the most success- 
ful result was obtained with distillate-oil emulsion of only 2 per cent. 
Field experiments failed, however, to justify the use of this wash alone, 
for it proved to lack the killing power found in the tobacco-extract 
sprays. The emulsion serves, however, as a very good " spreader" 
for the nicotine killing agent, since it serves to distribute the spray 
over the leaf surface. Commercial tobacco extract No. 2 proved to 
have greater insecticidal value than commercial tobacco extract No. 1, 
judging by the corresponding strengths of the two sprays; and there- 
fore in the field only the former was used. Foliage tests on an Eastern 
black walnut tree were made of all the washes used in the laboratory 
experiments, and in no case was any burning observed to result. This 
type of walnut seems more susceptible to burning injury than does 
the European or so-called "Persian" walnut. 
FIELD EXPERIMENTS. 
SPRING AND SUMMER TREATMENT. 
Experiment No. 1. — Lime-sulphur (commercial 1-50) combined with commercial 
tobacco extract No. 2 (1-1,500). Orchard of Mr. I. Du Bois, San Jose, Cal. Two large 
European walnut trees badly infested with aphides were sprayed July 1, 1911, under an 
even pressure of 170 pounds. A count made on the following day showed that 95 per 
cent of the aphides had been destroyed by the wash. 
Experiment No. 2. — Three per cent standard distillate-oil emulsion combined with 
commercial tobacco extract No. 2 (1-2,000). A large, badly infested European walnut 
tree in the yard of the experiment station at San Jose was treated, July 3, 1911, with 
this spray at an even pressure of 170 pounds. A count made July 5 showed that over 
95 per cent of the aphides had been killed. 
Experiment No. 3. — Commercial tobacco extract No. 2 (1-1,500). Orchard of Mr. 
F. Leib, near San Jose, Cal. (PL IV, figs. 1, 2). A block of 10 walnut trees badly infested 
was sprayed, May 21, 1912, under a pressure fluctuating from 60 to 140 pounds. A 
count made two days later showed that not over 40 per cent of the "lice" were de- 
stroyed . 
Experiment No. 4. — Commercial tobacco extract No. 2 (1-1,500) combined with 2 
per cent homemade distillate-oil emulsion. Orchard of Mr. F. Leib, near San Jose, 
Cal. A block of 10 badly infested walnut trees was sprayed, May 21, 1912, under 
pressure similar to that of experiment No. 3, A count made two days later showed 
that 98 per cent of the insects had succumbed. Some oil burning appeared on the 
foliage and nuts owing to insufficient agitation in the preparation of the emulsion 
and consequent freeing of oil. 
Experiments Nos. 3 and 4 were made to determine whether the tobacco extract 
alone would prove effective in the field. Results indicate that a weak solution of 
oil emulsion is necessary to act as a "spreader" for the tobacco. 
