CONTROL OF THE SAN JOSE SCALE 



SPRAYING EXPERIMENTS IN 1923 



A few tests of oil sprays were made in 1923, and scales were exam- 

 ined from several orchards sprayed by various growers. The results 

 of these examinations did not indicate that the 2 per cent emulsion 

 could be depended on to control the scale. In two tests, slightly 

 over 99 per cent of the scales were dead, but in the others the per- 

 centages killed ranged from 93 to 97. In even moderately infested 

 orchards, more than 99 per cent of the scales must be killed to effect 

 satisfactory control. 



It was found that the soap emulsions used in the East were very 

 likely, in the Pacific Northwest, to break down in the hard water 

 available for spraying. At the time the dormant spray is applied 

 in the Yakima Valley, water has usually not been turned into the 

 irrigation canals, and water for spraying must be secured from drain- 

 age ditches, wells, or cisterns. These waters are very hard, con- 

 taining, large quantities of calcium bicarbonate, magnesium bicarbon- 

 ate, and sodium sulphate. Even the irrigation water is usually some- 

 what too hard for use with the soap emulsions. Table 1 gives an 

 analysis of several samples of water, and shows the difference be- 

 tween irrigation water and the well water and drainage water. 

 These samples were collected in February, 1924, shortly before the 

 spraying season started. 



Table 1. 



-Analyses of waters used for spraying in the Yakima Valley, Wash. 

 February, 1924 1 



Constituents 



Irrigation 

 water, 

 Yakima 



Well water, 

 Grandview 2 



Drainage 



water, 

 Granger 2 



Total solids . - - - -- - - 



Parts per 

 million 

 59.8 

 7.8 

 2.0 

 62.0 

 2.6 

 22.3 



Parts per 



million 



891.6 



44.5 



110.9 



147.0 



77.0 



106.4 



Parts per 

 million 

 1, 184. 3 





51.4 





43.7 





340.7 



Sulphate radicle (S0 4 ) 



321.1 



Sodium (Na). . . - - _ - . . . . _ -_.... 



229.5 







1 These analyses were made by E. L. Green, formerly assistant chemist, Washington Agricultural Experi- 

 ment Station. 



2 These analyses are evidently incomplete, and it is suggested that chlorides were present but not deter- 

 mined. 



The large quantities of calcium and magnesium salts present in 

 the well and drainage waters decompose most of the potassium soap 

 in the oil emulsion, allowing the oil droplets to run together and 

 come to the surface as free oil. It is also probable that a certain 

 amount of inversion takes place. The calcium or magnesium soap 

 formed is more soluble in oil than in water; hence the oil-in-water 

 emulsion is changed to some extent to a water-in-oil emulsion which 

 will not mix with water. The decomposition of the soap is hastened 

 by the stirring of the dilute emulsion in the spray tank with the 

 agitator. Even without this agitation the emulsion is partially 

 broken down before it can be used. 



Soft water was used in the two tests mentioned above in which 

 less than 1 per cent of the scale survived, but in the others the water 

 was hard, and it was thought that this may have made the difference 

 in the control obtained., 



