SOME ENEMIES OF THE TREES 115 



age, however, is done to the foliage, by the for- 

 mation of the little yellowish cluster cups or 

 blisters, which destroy the functions of the leaf. 

 Cedar rust must have two hosts to complete its 

 life cycle. As the fruit trees cannot become in- 

 fected with this disease from any other source 

 than from cedar balls, the destruction of all the 

 red cedar trees in the fruit areas is the easiest 

 way to become free from the pest. 



Apple-scab is another fungus disease that 

 thrives in cool, moist weather. It is most trou- 

 blesome to fruit growers. Indeed it was to 

 combat this disease that spraying was first in- 

 augurated. It is caused by a fung^is which 

 feeds on tissues of the fruit and foliage. Its 

 presence on the fruit is shown by a series of cir- 

 cular, dark-gray spots, which in bad cases often 

 dwarfs the affected side, pitting and cracking it 

 out of all shape. Apple-scab attacks both sides 

 of the foliage, producing smoke-brown patches, 

 causing the leaf to curl and often to drop off. 

 Apple-scab lives through the winter on fallen 

 leaves, and starts growth in the early spring, 

 producing spores which are discharged into the 

 air and carried to the young leaves and blossom 

 buds, where they germinate and start infec- 

 tions. 



Bitter rot, another dreaded fruit fungus, ap- 



