4 CIRCULAR 17 5, U. S. DEPARTMENT OF AGRICULTURE 



SPRAYING EXPERIMENTS IN 1924 



A large series of spraying tests was made against the San Jose 

 scale in the spring of 1924. It was evident from the experience 

 of 1923 that the boiled lubricating-oil emulsion, made with potash 

 fish-oil soap, can not be recommended for use in the Pacific North- 

 west, except where soft water is available. Attempts to remedy 

 the difficulty by the use of stabilizers, such as more soap, flour, glue, 

 casein, weak Bordeaux mixture, and cresol, were not very successful. 

 The hard water can be softened by adding lye to it and allowing it 

 to stand for a day or two, but this is impracticable, as the growers 

 do not have storage tanks. 



It was known that various commercial miscible oils made of 

 lubricating or fuel oils, soap, and cresylic acid (cresol) mixed with 

 hard water much more readily than did the boiled lubricating-oil 

 emulsion. The possibility of making a "homemade'' miscible oil 

 was therefore investigated during the winter of 1923-24, and a 

 method was worked out which is given on page 10. It was found 

 that this miscible oil could be made without any pumping and with 

 very little or no heating. To be perfect, however, the various in- 

 gredients must be measured out accurately, and since the soap obtain- 

 able always contains some water, this water content must be known. 

 This soap is not ordinarily sold with any guaranty as to water con- 

 tent, and it is subject to drying if exposed to the air. It is therefore 

 difficult for an individual grower to make this miscible oil. 



A cheaper and more easily made oil spray than the miscible oil 

 is one that originated at the Missouri Experiment Station. 1 In mak- 

 ing this emulsion the oil is emulsified by means of calcium casemate 

 (casein spreader). This emulsion may be called the "casemate oil 

 emulsion." It has the advantages of being cheaply and easily pre- 

 pared by anyone capable of following simple directions, and also of 

 mixing perfectly with any hard water and even with lime sulphur. 

 It should be made up as needed, for it will not keep very well for 

 more than a week or two. 



In the tests made in 1921 lubricating-oil emulsions made with 

 soaps and with casein spreader were used, as well as the miscible oil 

 and commercial lime sulphur. The spray was applied with a bucket 

 pump to limbs of trees infested with the San Jose scale. Twigs 

 from these limbs were examined with a binocular microscope about 

 a month after the spray was applied, and a record was made of the 

 percentage of the scales that were dead, only the half -grown female 

 scales being considered. The results obtained are presented in Table 

 2. and the percentage of control is also given. This has been figured 

 in accordance with the method used by Abbott. Culver, and Morgan. 2 



1 Burroughs. A. M. a new method of making engine oil emulsions. Missouri Agr. 

 Expt. Sta. Bui. 205, S p.. iilus. 1923. 



"Abbott, W. S.. Culver. J. J., and Morgan. W. J. effectiveness against the san 



JOSE SCALE OF THE DRY SUBSTITUTES FOR LIQUID LIME-SULPHUR. U. S. Dept. AgT< Bui. 



1371, p. 6. 1926. 



