Diseases and Pests of the Apple and Their Control 221 



low wet ground or near irrigation ditches are sometimes 

 susceptible to collar-rot. 



In working about trees, care should be taken not to 

 scrape the bark or cause wounds at or about the collar. 

 Such wounds may permit the entrance of either sapro- 

 phytic or parasitic fungi. 



Observations have been made of the successful removal 

 of infected or rotted tissues after which bridge-grafting 

 or the planting and grafting in of young trees about the 

 base of the trees has resulted in the saving of many collar- 

 rotted trees. The practice, while recommended for iso- 

 lated cases, is hardly advisable on a large scale. The 

 process is expensive and not always successful. 



Fire-alight (Bacillus amylovorus). 



Fire-blight or pear-blight is a bacterial disease which 

 affects both apples and pears and, while less serious on 

 apples, it is responsible for heavy loss in apple regions. 

 The disease is caused by microscopic bacteria working just 

 underneath the bark in growing tissues of the trees. 



The presence of blight is generally evidenced during the 

 growing season by a wilting of the leaves and branches 

 above infected parts. The disease winters in hold-over 

 cankers which at the beginning of spring growth exude 

 drops of infected gum. Insects are attracted to the sweet- 

 ened gum and very often carry the germs with them from 

 flower to flower during the period of pollination. Bees 

 are well-known carriers of the disease and aphids very 

 often spread infection through feeding punctures. The 

 first sign of blight in the spring is usually apparent when 

 the infected blossom-spurs begin to wither and die, result- 



