DISEASES OF CROPS 



941 



under surface, in the late stages, are produced small, fringed, cup-like 

 structures containing great masses of spores. These spores will not re-in- 

 fect the apple, but are carried by the wind to neighboring red cedar trees, 

 where they cause the formation of the familiar cedar apples. 



These large brown cedar apples of the cedar, occurring in the spring, 

 produce gelatinous, horn- 

 like projections, bearing 

 masses of spores. These 

 spores are borne by the 

 wind to the apple tree, 

 which is re-infected with 

 the disease. 



Treatment. — Remove 

 the cedar apples, or still 

 better, remove the cedar 

 trees. Spraying the apple 

 trees as for scab will re- 

 duce the disease to some 

 extent. 



Fire Blight.— See 

 Pear. 



Other Foliage Spots 

 and Twig Cankers. —There 

 are leaf spots and twig 

 cankers due to other causes 

 which cannot be enumer- 

 ated in this brief discus- 

 sion. These diseases are 

 all more or less injurious, 

 but can be controlled by 

 the regular spraying 

 methods and sanitation. 



Mildew (Sphcerotheca 

 mali [Duby], Burr.) . — This 

 fungus grows on the sur- 

 face of the leaf, causing a 

 grayish or whitish covering. Usually it is not severe and can be con- 

 trolled by the regular spraying or by spraying with potassium sulphide. 



Crown Gall and Hairy Root (Bacterium tumefaciens, Smith and Town- 

 send). — -These two diseases are due to the same organism. The crown galls 

 or root galls occur at the crown or on the roots and sometimes on the 

 stems. They are more or less spherical, with irregular, roughened surfaces. 

 Some are hard and others soft, but they are all probably due to the same 

 cause. They are most severe on red raspberries, are very inj urious to peach 



1 Court esy of Pennsylvania Agricultural Experiment Station, State College, Pa. 



Apple Tree with Typical Collar Blight. 1 



.Showing proper method of cutting back into healthy 

 bark before treating with paint. 



