THE BLIGHT CANKER OF APPLE TREES 



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I. Cankers and What They Are. 

 During recent years several kinds of cankers, occurring especially 

 upon apple trees, have been described and figured in bulletins from differ- 

 ent experiment stations in this country. A canker of fruit trees has long 

 been known in Europe, due to the attacks of a fungus, Ncctria ditis- 

 sijiia.--'^' This disease has also been reported from America.^^ By careful 

 noculation experiments, these various cankers have been shown to be due 

 'to different species of either fungi or bacteria. Some of these canker 

 diseases are peculiar to certain regions only. Others are more cosmo- 

 politan and are likely to be fovmd wherever apple trees are grown. 



Notwithstanding the fact that these injuries to the bark of living 

 trees have been, in the large majority of cases, absolutely proved to be 

 due to the growth of parasitic fungi or bacteria, growers very generally 

 even at the present time attribute them to " sun scald " or " winter injury." 

 Lack of knowledge of the nature of fungous and bacterial growth, to- 

 gether with the ease with which responsibility may be shifted upon the 

 weather, have made this opinion the common and natural one. Not only 

 have experiment station workers shown that these injuries are usually 

 due to the attacks of living organisms rather than to the results of un- 

 favorable weather conditions, but they have demonstrated that the differ- 

 ent forms of these cankers are due to distinctly dift'erent organisms. 



The term '* canker," then, has come to be a very general one and is 

 applied to diseases which cause the death of definite areas of bark on the 

 limbs and bodies of trees. The diseased area may be smooth and sunken 

 or enlarged and roughened, depending on the nature of the organism 

 causing it. Alost " cankefs," as the term is understood at the present 

 time, are caused by the attacks of some parasitic plant, either a fungus or 

 bacterium. 



The following distinct canker diseases of apple trees have been 

 described. Those marked with a f are known to occur in this State : 



tEuropean canker" (Nectria ditissima Tul.). 



tNew York Apple Tree Canker'" (Sphaeropsis malorum Pk.). 



Blnck Spot Canker" (Gloeosponum malicortics Cordley). First described by 

 Cordlcy in igoo as "Apple Tree Anthracnose '''°. Also referred to as Pacific coast 

 canker. 



Illinois Apple Tree Canker'' (Nummularia discreta Tul.). 



Bitter Rot Canker^ (Glomerclla rufomaculans (Berk.) Spal. & v. Scbr.). 



tBlight Canker of apple trees'" (Bacillus amylovorus (Burr.) de Ton!.). 



It is to the last of these, the Blight Canker, that this bulletin is espe- 



* These numbers refer to the bibliography at the end of this bulletin. 



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