104 AGRICULTURE FOR BEGINNERS 



First, how will you recognize this disease? If the dis- 

 eased bough at which you are looking has true fire blight, 

 you will see a blackened twig with withered, blackened 

 leaves. During winter the leaves do not fall from blighted 

 twigs as they do from healthy ones. The leaves wither 

 because of the diseased twig, not because they are them- 

 selves diseased. Only rarely does the blight really enter 

 the leaf. Sometimes a sharp line separates the blighted 

 from the healthy part of the twig. 



The fire blight is caused by bacteria, of which you have 

 read in another section. These bacteria grow in the juicy 

 part of the stem between the wood and the bark. This 

 tender, fresh layer is called the cambium, and is the part that 

 breaks away and allows you to slip the bark off when you 

 make your bark whistle in the spring. The growth of 

 new wood takes place in the cambium, and this part of 

 the twig is therefore full of nourishment. If this nourish- 

 ment is stolen, the plant of course soon suffers. 



The bacteria causing this disease are readily carried 

 from flower to flower and from twig to twig by insects, and 

 to keep all bacteria away from your trees you must see to 

 it that all the trees in the neighborhood of your orchard 

 are kept free from mischievous bacterial enemies. If they 

 exist in near-by trees, insects will carry them to your 

 orchard. You must therefore watch all the relatives of the 

 pear ; namely, the apple, hawthorn, crab, quince, and moun- 

 tain ash, for any of these trees may harbor the germs. 



When any tree shows blight, every diseased twig on it 

 must be cut off and burned in order to kill the germs, and 

 you must cut low enough on the twig to get all the bac- 

 teria. It is best to cut a foot below the blackened portion. 



