iSi 



JBULLETIN 236. 



cially devoted. Although this particular kind of cankered spots on apple 

 trees was probably first observed by horticultural writers as early as 1780^^ 

 and has been repeatedly referred to in horticultural writings since that time, 

 its true nature does not seem to have been suspected until 1880. In that 



year Professor T. J. Burrill, of the 

 Illinois State Experiment Station, 

 while working on the fire blight of 

 pears and apples, came to the conclu- 

 sion that the so-called " sun scald " 

 spots on the bodies and larger limbs of 

 apple trees are due to the same cause. 

 At a meeting of the Illinois State Hor- 

 ticultural Society in 1881^ in answer 

 to a query regarding the nature of 

 " sun scald," he said : " The sun scald 

 on apple tree is the same as pear 

 blight." Similar statements of Pro- 

 fessor Burrill upon the same sub- 

 ject are recorded in other places.^ 

 Upon what experimental evidence, if 

 any, this and other statements^ were 

 based I have so far failed to discover. 

 A number of writers^ since that time 

 have referred to these cankered patches 

 as "body blight" due to attacks of 

 Bacillus amylovorous,^'^ but none seem 

 to have actually produced the cankers 

 by the introduction of the bacteria into 

 the bark of healthy trees. ^^ 



Fig 



49. — Typical blight canker on 

 main limb of young tree. 



2. The Distinguishing Characters and Appearance of the Canker 



The blight canker (Fig. 49), while it may occur on trees of almost 

 any age, is most destructive on young trees just coming into bearing, trees 

 from 8 to 15 years old. In some sections of this State, notably the 

 Upper Hudson River valley, at least 95 per cent of the trees of this age 

 show canker on limbs or body. A very large percentage of the affected 

 trees are dead and the remainder are fast succumbing. \^ery noticeable 

 throughout this section also are the large number of trees with cankers 

 in the crotches (Fig. 50) where the main limbs arise from the body. In 

 this same region a good sized orchard, set out about three or four years 

 ago, was observed to have suffered severely evidently from this same 

 disease. In this orchard the disease usually involved the greater part of 



