12 



the same way, there were 15 per cent scabby leaves on the check trees and 3 to 

 4 per cent scabby leaves on the dusted trees. In the third orchard, where no pre- 

 pink appUcation was used, there were at this time 53 per cent scabby leaves on 

 the check and 21 to 24 per cent scabby leaves on the dusted trees. This indicates 

 the necessity of a prepink application if dust is to control the primary infection. 

 But even where both prepink and pink applications of dust were made, relatively 

 more primary infection occurred than in the sprayed orchards. As is explained 

 elsewhere, the dust treatments in the orchards where dusting began with a pre- 

 pink application, were entirely satisfactory in preventing the further spread of 

 scab, that is, in preventing infection later in the season by the summer spores. 

 It would appear that if dust is equally as efficient as Uquid spraying in controlling 

 the spread of scab during the summer, it is less efficient in preventing the primary 

 infection in early spring. If such is the case, then for those who own both duster 

 and sprayer, a safer procedure would be to use the sprayer for the pink appUcation 

 and the duster for later ones. It should not be overlooked, however, that dust 

 satisfactorily controlled scab on the fruit when the dusting schedule included both a 

 prepink and pink appUcation. 



Effect of Fungicides on the Tkee. 



The literature contains references to increased dropping of the fruit foUowing 

 the use of lime-sulfur. There was this year in the experimental orchards no more 

 dropping of the fruit foUowing any of the several treatments than that wliich 

 occurred on the check trees. 



There was only a negligible amount of injury to fruit or foliage on any of the 

 sprayed or dusted plots. The trees used are Mcintosh. Although burning was 

 absent in the experimental plots, it was seen on the fruit of Baldwins following 

 the appUcation of sulfur dust. Childs (3) and others report that sulfur dust may 

 cause an injury to apple fruit similar to that of Ume-sulfur solution. The relation 

 of sulfur dust burning to temperature in the case of varieties susceptible to burn- 

 ing needs to be further considered. As has been pointed out by Safro (24) some 

 cases of injury attributed to Ume-sulfur are primarily cases of sunburn, and the 

 same is probably true of injury by suKur dust. The absence of spray injury from 

 all plots made it impossible to learn to what extent the addition of lime to Ume- 

 sulfur decreases burning, and how the latter fungicide compares with Atomic 

 Sulphur in tliis respect on the apple. 



Relation of Temperature of the Season to the Fungicidal Efficiency of 



Sulfur. 



We have as yet no data on the temperature necessary for sulfur to prevent the 

 germination of the winter spores of the apple scab fungus. Doran (25) has shown 

 that sulfur prevents the germination of the summer spores of this fungus when 

 the temperature is 78.8° F. for five hours. If the temperature is higher, less time 

 is necessary and if the temperature is lower, more time is necessary. This tempera- 

 ture or above it was recorded in the experimental orchards on fifty days between 

 May 7 and August 31. As the results show, the temperature conditions of the 

 season were such as to insure the fungicidal action of sulfur, and so prevent the 

 germination of the conidia. 



If there had been fewer days during this period when the temperature reached 

 the necessary point, it is probable that the results with Bordeaux mixture_ and 

 copper dust as compared with sulfur fungicides would have appeared relatively 

 better than proved to be the case. 



Summary. 



A spray schedule beginning with the pink application controlled apple scab as 

 well as a schedule beginning with the prepink application. 



Sulfur dust controlled apple scab satisfactorily when it was applied five times 

 beginning with the prepink application, but not when it was appUed four times 

 beginning with the pink application. 



Liquid Ume-sulfur 1-50 and dry Ume-sulfur 4-50 proved of equal fungicidal 

 eflEiciency for scab control. 



Less than 4 pounds of dry Ume-sulfur in 50 gallons did not on the whole control 

 scab quite as weU as dry lime-sulfur 4-50. 



