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. (PI. 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. Eesults indicate that a weak solution of 

 oil emulsion is necessary to act as a "spreader" for the tobacco. 



