6 CIRCULAR 17 5, U. S. DEPARTMENT OE AGRICULTURE 



3 per cent oil spray is much more effective than the 2 per cent oil. 

 The presence of a small amount of the scale in the first two blocks is 

 probably due to a failure to cover the trees thoroughly in spraying, 

 or to infestation that spread from other trees during the summer. 



SPRAYING EXPERIMENTS IN 1925 



In 1925 a series of experiments was made to test the comparative 

 value of oil emulsions diluted to 2, 3, 4, 6, and 8 per cent of oil. A 

 comparison was made, at the 2, 3, and 4 per cent strengths, of the 

 cold-mixed casemate oil emulsion, the boiled emulsion prepared with 

 soap, and the miscible oil. The boiled emulsion used in these tests 

 was prepared at the United States entomological laboratory at Fort 

 Valley, Ga., and shipped to Yakima. A red engine oil having a 

 Saybolt viscosity of 227 seconds was used. Brown neutral oil was 

 used in making the caseinate emulsion and the miscible oil. This 

 had a viscosity of 116 seconds. The other characteristics of these 

 oils are given on page 11. These tests were made with a bucket 

 pump, and the scales were examined about one month later. This 

 series of experiments was carried out twice, once on February 24 and 

 again on March 13. The results of the two series of tests were 

 averaged and are given in Table 3. 



Table 3. — Results of experiments with lubricating-oil and lime-sulphur sprays 

 on the San Jose scale on apple trees, Yakima, Wash., 1925 



[Approximately 1,500 scales examined in each test] 



No. 



Materials used 



Dilu- 

 tion 



Tests 

 made 



Scale 

 dead 



Con- 

 trol 



1 

 2 



Lubricating-oil (brown neutral) 1 emulsion (casein emulsifier) 2 



Do .- 



Per cent 

 oil 

 2 

 3 

 4 

 6 

 8 

 2 

 3 

 4 

 2 

 3 

 4 

 °B. 

 4 



Num- 

 ber 

 2 

 2 

 2 

 1 

 1 

 2 

 2 

 2 

 2 

 2 

 2 



2 



2 



Per cent 

 90.3 

 98.8 

 99.6 

 100.0 

 100.0 

 91.3 

 98.7 

 99.7 

 91.4 

 97.3 

 99.1 



95.3 

 49.5 



Per cent 

 80.8 

 97.6 



3 



Do -. 



99.2 



4 



Do 



100.0 



5 



Do 



100.0 



fi 





82.8 



7 



Do . 



97.4 



8 



Do . 



99.4 



9 



in 



Lubricating-oil (eastern red engine) 4 emulsion (soap emulsifier) 6 .-- 

 Do 



83.0 

 94.7 



ii 



Do 



98.2 



12 





90.7 



IS 



Check - --- 













i See specification No. 6. (p. 11). 



2 See formula No. 2 (p. 9). 



3 See formula No. 3 (p. 10). 



4 See specification No. 9 (p. 11). 

 « See formula No. 1 (p. 9). 



Very little difference is evident in the three types of oil sprays. 

 The results from the cold-mixed caseinate oil emulsion and from 

 the miscible oil are practically identical. The boiled emulsion, pre- 

 pared with soap, gave slightly poorer results than the others with 

 the 3 and 4 per cent dilutions. 



The emulsions used at a dilution of 2 per cent of oil gave rather 

 poor results, 9 or 10 per cent of the scales remaining alive. At 3 per 

 cent the results were much better, only 1 or 2 per cent of the scales 

 surviving, while at 4 per cent less than 1 per cent of the scales sur- 

 vived. The 6 and 8 per cent dilutions of the caseinate oil emulsion 

 resulted in a complete mortality of the scales. Lime sulphur at a 

 dilution of 4° Baume left about 5 per cent of the scales alive. 



