April, '21] GiDDiNGS: dusting vs. spr.wing 227 



(Orchard No. 2) 

 Foliage data: 

 Leaf spot 



(Percent, leaves diseased) 80.0 32.9 60.4 



Leaf spot 



(Spots per infected leaf) 20.8 2.8 5.0 



Percent, scabby leaves 53.6 7.7 14.9 



Fruit data: 



Percent, scabbv fruit (total) 95.2 21.5 90.5 



Percent, light scab 18.3 8.1 39.6 



Percent, sooty blotch 99.5 5.0 89.9 



Please note that the results from use of sulphur-lime sulphur dust are 

 included merely because they indicate a hopeful line for further experi- 

 mental v^^ork. The combination of natural conditions which helped to 

 bring about these results may have been far from normal, but we are 

 inclined to believe that such was not the case. 



Otir results have indicated that sulphur dust is not so effective as 

 either the lime sulphui spray or the Bordeaux spray for control of apple 

 scab in West Virginia orchards where the disease is severe. 



We have found that it is absolutely essential to apply the dust in the 

 early morning, and undoubtedly it would be preferable to apply it soon 

 after midnight as some are already doing. We have found that the dust 

 machines available do not have sufficient power and do not expel the 

 dust with sufficient force. We believe that the discharge tube could 

 well be arranged so as to give better distribution of the dust as it leaves 

 the machine. 



We have also found that appHcations of different materials must all be 

 made on the same day if any comparisons are to be considered. We 

 have a large am.ount of data, including special experiments, which shows 

 that a diflerence of one to three days between the dates of appHcation 

 of various materials or between applications of the same material will 

 often decrease or increase the relative effectiveness to such an extent as 

 to indicate clear-cut success on the one hand and extreme failure on the 

 other. 



Turning now to a general'survey of the work, I will endeavor to inter- 

 pret it from m.y point of view. I hope to keep within reasonable bounds, 

 for this idea of interpreting the other fellow's data is a ver>^ dangerous 

 pastim^e. Considering, first, the 1920 season, Michigan and Virginia 

 present strong evidence as to the value of sulphur dust against apple 

 scab. In Virginia seven applications of material were given. It seems 

 to me that we should reduce this number of treatments. Pennsylvania 

 reports good results from dust in two orchards and just fair comparative 

 control in a third. Five applications were given in each of these or- 

 chards. 



