BLIGHT CANKER OF APPLE TREES. 



H. H. Whetzel, Assistant Professor of Botany. 



Cankers in one form or another on apple trees are familiar to 

 most orchardists. As the term is generally understood to-day, 

 we mean by a canker a dead area in the living bark of the body 

 or main limbs of trees. This area may be sunken and smooth or 

 it may be swollen and rough. (Fig. 1 and 2) . The term " canker," 

 as used to-day, applies usually to diseases of trees that are caused 

 by parasitic fungi or bacteria. Altho these injuries to the bark 

 of living trees have been, in the large majority of cases, abso- 

 lutely proven to be due to the growth of fungi or bacteria, grow- 

 ers very generally attribute them to " sun scald " or " winter 

 injury." Not only have experiment station men shown that these 

 injuries are due to the attacks of living organisms rather than 

 to the results of unfavorable weather conditions, but they have 

 demonstrated that the different forms of these cankers are due 

 to distinctly different organisms. 



Of the two common cankers in the State the best known is the 

 New York Apple Tree canker. This is very prevalent in the 

 orchards of Western New York. It has long been known to 

 growers but the true cause of it was first worked out by Pad- 

 dock of the New York State Experiment Station at Geneva in 

 1899. It is caused by a fungus, Spliaeropsis malorum, and is in 

 most respects very different from the blight canker. In the early 

 stages of this canker concentric cracks appear in the outer skin 

 of the diseased area. (Fig. 3.). The cankered surface is always 

 black and roughened and covered with minute black pimples, 

 which are the fruit bodies of the fungus, often not so evident in 

 oldi cankers. These occur, for the most part, on the main limbs 

 of trees in old orchards, causing the death of limbs here and 

 there on the tree (Fig. 4). 



There is another canker wli ich is very severe thruout the State, 

 especially in certain sections. This we have named the Blight 

 Canker. The surface of this canker is sunken with a cracked 



