MANUAL OF GENEEAL AGEICULTUBE. 85 



or nearly so, prying off the cuticle and applying its my- 

 celium closely to the host tissue. 



Control. One spraying just before and one immedi- 

 ately after blossoming are most important for its control. 

 If the scab is serious it may be necessary to spray a third 

 time. The spray used is known as Bordeaux Mixture. It 

 is made of copper sulfate and lime. Directions for its 

 preparation are given in any of the references in Part V. 



68. FIRE BLIGHT. 



Materials : Read the experiment. Obtain Cornell Uni- 

 versity College of Agriculture, Bulletin 272. In sections 5 

 and 6 obtain specimens at blossoming time and press them. 

 Later in 7 obtain fruit and preserve in a five per cent solu- 

 tion of formalin, to which has been added enough copper 

 sulfate to just color the water. The latter will hold the 

 color in the fruit. Whenever possible fresh material 

 should be used. 



This is the most common and best known bac- 

 terial disease of plants occurring in this country. It 

 affects apples, pears, quinces and occasionally plums, apri- 

 cots, and a few ornamental and wild plants related to the 

 apple family. The affected tissues are killed outright. 



Symptoms. The symptoms of this disease will be 

 studied in the order in which they manifest themselves 

 during the season on different parts of the tree, beginning 

 with the first activity of the disease in the spring. 



The hold-over canker is the source for the first infec- 

 tion in the blossoms in the spring. Typical cankers on the 

 limbs of apple and pear trees have been provided. Study 

 the specimens before you carefully and observe : 



1. The smooth, more or less sunken area in the bark, 

 its margin sharply defined by a definite crack in the epi- 

 dermis the canker. In active cankers this margin is not 

 sharply defined. Note the diseased spur or shoot at the 

 center of each canker. 



