125 



The Effect of Cold Winters on San Jose Scale 

 AND Scale Sprays 



All examination of the foregoing tables will show considerable vari- 

 ation from year to year in winter mortality. The counts of live scale 

 for the four years on untreated branches were as follows : 



Year Percent alive 



1921-22 50.4 (March) 



1922-23 65.9 (April) 



1923-24 41.4 (March) 



f29.3 ( Tanuarv) 



1924-25 -{13.0 (February) 



[lO.O (March) 



It would seem entirely plausible that with the weakening effect of a 

 cold winter on scale, the sprays would be more effective. The tables pre- 

 sented here seem to indicate that this is true. In the fall tests in 1923, 

 given in Table VTII, the percent of live scale runs higher than in the 

 spring tests (1924) given in the same table. 



During this season we had a rather unusual experience in making 

 scale counts. Previously, after applying sprays, a month had been found 

 long enough to wait for the drying up of the scales that had been killed. 

 Following the fall applications of this year, however, there was a period 

 of abnormally cold weather, and on starting our counts after the usual 

 interval, the oil-sprayed branches showed from 22 to 36 percent of the 

 scale apparently alive. After another four weeks, branches with the 

 same treatment showed only 1.3% to 1.8% live scale, indicating that 

 the scales had been kept in cold storage, as it were, the continuous cold 

 preventing their drying sufficiently to show any discoloration. The win- 

 ter of 1924-25 was the most severe on the San Jose scale of any winter 

 since 1917-18, and the record of only lO'/i live scale on the check branches 

 in southern Illinois in March is remarkably low. The effect of this win- 

 ter-killing is indicated by the very small percent of live scale shown in 

 Table XI for that year, in which none of the treatments, with the excep- 

 tion of two very poor emulsions, gave less than 99% dead scale. 



SuMMARV and Recommendations 



This report gives the results of four years experiments on the con- 

 trol of San Jose scale at various points in southern Illinois. 



The superiority of oil sprays over lime sulfur was demonstrated, 11% 

 of the scale remaining alive after being hit with lime sulfur, as compared 

 with less than 2% with most of the oil sprays. 



Boiled emulsion was as effective as the various miscible oils used. 



Cold-mixed oil emulsions were about as effective as the boiled emul- 

 sions, but somewhat more unstable. 



The most reliable type of homemade emulsions are the boiled soap- 

 emulsions. 



