THE PRINCIPAL DISEASES 113 



Fortunately the scab fungus is comparatively easy to 

 fight. At least it is in most years. There are occa- 

 sional seasons when it seems to be epidemic and beyond 

 control. Under all ordinary circumstances thorough 

 and timely applications of bordeaux mixture will en- 

 tirely subdue it. The most useful application, however, 

 is the dose of plain copper sulphate solution given just 

 before the buds open. At that time the spores are rest- 

 ing on the apple buds, and this is just where, a few 

 days later at budding time, the most serious fungous 

 invasion occurs. Later applications of bordeaux serve 

 to check the spread of the fungus. 



Apple Tree Canker The apple tree canker has only 

 recently been recognized as a serious disease. Even yet 

 it is not present in all orchards to such an extent as to 

 cause much damage. Young orchards and sections 

 where apple growing is a new industry are apt to be 

 comparatively free. But in nearly all old orchards 

 there is an abundance of canker, and in the old apple- 

 growing sections, where neglected apple trees are as 

 common as flies in a country hotel, the canker is a well- 

 established and ever-present menace to the business. 



The canker appears in the form of large patches of 

 dead bark, more frequently in the crotches. Sometimes, 

 however, small canker spots can be seen on young 

 branches. As the canker eats in during the course of 

 two or three years, the bark peels off, leaving patches 

 of exposed wood. These are rough, and the edges are 

 black, and more or less wrinkled. This wrinkling along 

 the margins of the canker spots is particularly striking 

 in cases of long standing, where it is emphasized by the 

 successive annual attempts of the tree to cover in, and 

 heal the canker sore. 



