DUSTING AND SPRAYING EXI'EIMMENTS OP 



1920 AND 1921. 



Special Bulletiu No. 115. 



PY W. C. DUTTON AND STANLIOY .TOIINSTON. 



Pre-Pink Spraying op Apples. 



The general recommendation and practice of growers in Michigan for the 

 control of apple scab have not included any application before the blossom 

 buds have separated in the cluster. A few growers have delayed the dormant 

 application until the blossom buds were first swelling, thinking it to be bene- 

 ficial in controlling scab when applied at that time. An occasional grower 

 has followed the practice of making an application when the buds had ad- 

 vanced far enough for each bud to be easily seen but before they had sepa- 

 rated in the clusters. This is the stage of development referred to hereafter 

 as the "pre-pink" stage. 



Studies made in several dusting and spraying experiments during 1920 

 and 1921 indicated that, in many instances, scab infection had occurred 

 previously to the time the pink or cluster application was made. 



Life history of scab. Apple scab is carried through the winter on the 

 leaves which have dropped to the ground the previous fall. As soon as the 

 leaf drops, the scab mycelium spreads from the infected spots to all parts of 

 the leaf. In the autumn and early spring, organs known as perithecia are 

 formed and in these perithecia the spores develop and mature, ready to be 

 discharged when conditions are right. The discharge of these spores depends 

 upon their maturity and the occurrence of rainy periods after they are mature. 

 They may become mature but remain in the leaf for some time because of 

 the prevalence of dry weather. 



Spore discharge studies. The general recommendation that the first 

 spray application be made after the buds had separated in the cluster has 

 been based on the supposed fact that these spores were not mature and 

 hence could not be discharged until after the buds had reached the cluster 

 stage. Studies made in several experiments indicated that scab infections 

 were occurring earlier than the cluster stage. 



An experiment was planned for 1921 to determine if a pre-pink application 

 is necessary. Information was desired as to the exact time the spores are 

 mature and may be discharged, and studies to obtain this information were 

 made by C. W. Bennett of the Botanical Section. A report of these studies 

 is not to be included here but a brief statement of results may well be made. 



The Duchess orchard on the farm of Mr. J. C. Maynard, of Grand Rapids, 



