REPORT OF THE SOCIETY 43 



Conditions Favoring the Development of Fire Blight. 



This disease develops specially under hot and moist conditions, and its 

 development is more rapid in the tender parts of a tree, such as the blossoms, 

 twigs, suckers, etc. For rapid multiplication this bacterial organismn 

 needs a certain amount of humidity, and finds, therefore, a good medium 

 for such rapid development in young shoots and twigs of a tree where sap 

 is abundant. This is the cause of the noticeable spreading in these parts. 

 The disease is also more plentiful in orchards where rich and well cultivated 

 soil enables the trees to make a rapid and vigorous growth. On the contrary 

 cold and dry conditions stop the spreading of Fire Blight, as does a lack of 

 sufficient moisture in the soil. 



General Appearance of Fire Blight. 



The general appearance of Fire Blight may be discussed under four 

 heads : 



A — Body Blight, or the disease of the trunk and limbs. 

 B— Twig Blight. 

 C — -Blossom Blight. 

 D— Fruit Blight. 



Body Blight. 



When a tree becomes diseased with Body Blight, the affected bark 

 turns a dark blue color, starts to swell, and from these swellings there 

 exude numerous drops of a brownish, sticky liquid which run down the side 

 of the tree in small rusty streams. Often the bark becomes badly blistered. 

 The epidermis dries up and falls ofT, due to the death of the tissues. If such 

 a bark is pressed with the fingers it feels soft and spong^'. When a diseased 

 area is cut into, the first thing noticed is the abundance of moisture in the 

 fleshy bark and cambium. A deeper cutting shows the diseased cambium 

 to be streaked with red. 



Twig Blight. 



This form of the disease may occur in foliage twigs, blossom twigs 

 and suckers. In the majority of cases it develops from the blighted blossoms, 

 but after this it is directly due to inoculation by sucking insects, which 

 have previously been feeding on diseased twigs or suckers and have carried 

 some of the bacteria on their mouth parts and introduced them into the heal- 

 thy shoots. The appearance of the foliage in this stage of the disease has 

 given Pear Blight the common name of Fire Blight. When the germs are 

 introduced into the tender tip of a twig, they at once become active, and 



