80 DISEASES OF ECONOMIC PLANTS 



like projections, each bearing myriads of spores, which, 

 when conveyed by the wind to the susceptible apple tree, 

 cause the apple rust. Evidence that this relation really 

 exists is readily found if one examines an orchard having 

 red cedar trees upon its windward boundary. 



It is clear that the more red cedar trees there are in the 

 neighborhood of an orchard, especially to windward, the 

 more probability there is of damage from the rust. The 

 rational treatment, therefore, is to remove these trees in 

 so far as possible. 



In rare instances spores may be carried several miles, 

 but orchards are reasonably secure if all possibility of in- 

 fection from the immediate neighborhood be removed. 

 In case the red cedars are too numerous, or if for other 

 reasons it is impossible to cut them, spraying the tree as 

 recommended for the apple scab will lessen the evil to some 

 extent, but its success is not complete or certain. 



Resistant apple varieties are : Duchess, Sweet June, 

 Yellow Transparent, Red Astrachan, Ben Davis, Maiden 

 Blush, Winesap, Oldenburg, Gano, York Imperial. The 

 following are more susceptible : Wealthy, Red June, 

 Wliitney, Jonathan, Missouri Pippin, Prairie Crab. 



Blight {Bacillus amylovorus (Burr.) De Toni). — De- 

 scription and discussion of this disease will be found on 

 page 101 under Pear, the blight of which is identical with 

 the apple disease. Its character and treatment are the 

 same upon both hosts. While the blight is preeminently a 

 pear disease, it also affects the apple very seriously, par- 

 ticularly the form of " "body blight " upon the trunk. 



The Lowell, Isham, Smith Cider, and Yellow Transpar- 

 ent are especially susceptible varieties, while the Celestia, 



