Report of State Board of Horticulture. 93 



superficial canker; but with the advent of warmer weather 

 in spring, with its induced physiological activities, they nvdy 

 increase in size rapidly until, under favorable conditions, the 

 disease may invade an area several inches in diameter by the 

 last of May or early June. At that time the increase in size 

 of the canker spots and the energies of the fungus are thence 

 devoted wholly to the production of spores. At that time 

 the diseased areas are dark brown in color, markedly de- 

 pressed, and usually limited by ragged irregular fissures 

 which separate the dead from the surrounding living tissues. 

 (See Fig. 8.) These dead spots vary in size from those not 

 more than one-half inch in diameter to extensive areas three 

 or four inches wide by six or eight long. Even larger diseased 

 areas are sometimes produced by the union of two or mcra 

 cankers. 



EXTENT OF INJURY. 



It is difficult to form an estimate of the extent of the injury 

 caused by this disease. To be sure, orchards have been com- 

 pletely ruined by it, but in the vast majority of orchards its 

 presence is indicated only by more or less numerous ugly 

 wounds upon the branches. Occasionally a single canker com- 

 pletely girdles a branch on the trunk of a young tree, thus 

 killing at once its distal portion (See Fig. 10), but more com- 

 monly only a dead spot occurs from which in the course of a 

 few months the bark sloughs oflf, leaving an ugly wound which 

 requires several years to heal. (See Fig. 9.) When these 

 wounds were at all numerous the branches are much dis- 

 figured and are moreover greatly weakened. It is not at all 

 uncommon, however, for trees which have been seriously 

 injured to continue to bear fair crops of fruit year after year. 



CAUSE OF THE INJURY. 



Many theories have been advanced regarding the cause of 

 this disease, among which may be mentioned insect injury, 

 sour sap, frost, sun-scald, fire blight, etc., and indeed most of 

 these causes may produce injuries which superficially resem- 

 ble apple tree anthracnose in its early stages. There is no 

 longer any doubt, however, that this disease is produced by 

 a particular fungus, Gloesporium malicorticis. 



