Blight Canker of the Apple Tree. 215 



14. Resistant and Susceptible Varieties 



Early in the investigations it was observed that certain varieties are 

 more susceptible to attacks of the canker than others. Fortunately, in 

 the orchards examined there was in each case a number of varieties repre- 

 sented so that considerable data as to relative resistance was secured. 



Only one variety so far has been observed that seems to be entirely 

 immune to canker attacks. In an orchard of some 200 trees in the worst 

 infected section of the Hudson River region, all the trees had gone out 

 but seven. These were Wolf River. They showed not a single canker 

 and were strong and thrifty. A single tree of this same variety was also 

 observed in another orchard in the same locality. It, too, was entirely 

 free from the disease. The Wolf River is not regarded as a desirable 

 fruit but could be used to advantage as stock for top-grafting. By 

 setting desirable varieties well out on the main limb the chief source of 

 trouble would be removed. Talman Sweet, although not entirely im- 

 mune, appears to be fairly resistant and as stock for top grafting seems 

 to be valuable. 



A provisional arrangement of varieties so far observed in the order 

 of their resistance may be said to be : Wolf River, Talman Sweet, Pewau- 

 kee, Red Astrachan, Tetofsky, Grimes Golden, Wine Sap, Fameuse. 



In most of the afifected orchards the Baldwin was the first to go out 

 from canker attacks. The Ben Davis seems to be almost as subject to 

 the disease as the Baldwin. The susceptibility of this variety to the so- 

 called '■ sun scald" has been reported by growers in the ^lississippi val- 

 ley.^ The more susceptible varieties seem to be : Baldwin, Ben Davis, 

 Mann, Ilubbardston, Fall Pippin, Stark, Greening. 



In general, summer and fall varieties seem to be less liable to attacks 

 of the disease, or at least suffer less, while winter varieties are apparently 

 more susceptible. It may be mentioned here that the writer has observed 

 this same peculiarity in the attacks of the apple rust, the roestelia stage of 

 Gymnosporangium macropus. 



The study of varietal resistance has not been extensive and the above 

 lists are to be regarded as entirely provisional. Further observation along 

 this line will no doubt very materially change the number and arrangement 

 of varieties. Enough has been observed, however, to indicate that it 

 ofifers valuable suggestions to growers in regions known to be especially 

 subject to canker epidemics. 



15. Acknowledgments 

 The writer takes this occasion to acknowledge the many kindnesses 

 and courtesies extended to him by growers whose orchards he has had 

 occasion to examine. He is especially indebted to Air. L. B. ,Frear of 



