APPLE POWDERY MILDEW. 



19 



The method of measuring the degree of control of foliage infec- 

 tion was the same as in the earlier work. The results again showed 

 the effectiveness of the sulphur sprays and indicated that in seasons 

 like that of 1917 good mildew control may be established by careful 

 and thorough spraying with either lime-sulphur solution, colloidal 

 sulphur, or sulphur in some other finely divided form, if the fungi- 

 cides are applied at the time the buds are in the " pink " and again as 

 soon as the petals have fallen. These experiments also demonstrated 

 that there is little difference in the efficiency of Bordeaux mixture 

 and ammoniacal copper carbonate for mildew control, but both are 

 less efficient than the sulphur sprays. In the case of the Bordeaux 

 mixture, the same objection arose as in previous years, i. e., apples 

 sprayed with it failed to develop a good red color. For this reason, 

 therefore, if it is necessary to spray for mildew after the advent of 

 hot, burning sunlight, ammoniacal copper carbonate is to be pre- 

 ferred to the sulphur sprays. 



In 1917, for the first time since the experimental work was begun, 

 a fair crop of fruit was obtained on the Pryor Eeds and gave the 

 first opportunity to obtain data on the effects of spraying in the re- 

 duction of mildew russeting of the fruit. Yfhile the Pryor Eed 

 variety is less subject to russeting than some others, and while there 

 was only a small amount of the trouble even on the check trees, the 

 results, as shown in Table III, indicate that the russeting can be 

 eliminated by proper spraying. This is a matter of considerable im- 

 portance with such solid-color and high-grade varieties as Grimes, 

 Jonathan, Newtown, and Esopus (Spitzenbiorg) , and with others 

 where the marking is prominently displayed, and causes a loss of 

 grade and lowered returns. The efficiency of the different sprays in 

 preventing mildew russeting of the fruit proved to be about the same 

 as in the case of foliage infection. 



In 1917 it was also possible for the first time to compare the cumu- 

 lative effects of the different sprays used in previous years in the 

 prevention of bud blight and in insuring a crop of fruit. These data 

 were obtained only in the case of the Pryor Eed variety and are pre- 

 sented in Table IV. The plat numbers refer to the designations of 

 the plats in 1916. 



Table IV. — Average yield of fruit per tree of the Pryor Red variety in 1917, 

 showing the cumulative effects of different sprays used in previous years for 

 the control of apple powdery mildew at Wenatchee, Wash. • 



Plat. 



Average 

 yield. 



Crop in- 

 crease 

 over 

 check. 



Plat. 



Average 

 yield. 



Crop in- 

 crease 

 over 

 check. 



No 8 



Bushels. 

 18 

 22 

 18 

 15 

 17 



Per cent. 

 50 

 83 

 50 

 25 

 42 



No. 13 



Bushels. 



20 



11 



16 



a 12 



Per cent. 

 66 





No. 14 





No 10 



No. 15.... 



33 





No. 16 





No. 12 











a Check. 



