Sept. 8, 1923 
Origin and Control of Apple-Blotch Cankers 
413 
It has been observed among trees of the same variety in the same 
orchard that blotch is more severe in some than in others and that this 
relative difference between individual trees remains more or less constant 
year after year. This phenomenon is illustrated by the data of 1920 and 
1921 on four unsprayed Northwestern trees, presented in Table VIII. 
Table VIII .—Individuality of trees in degree of infection 
Tree. 
Percentage of petiole 
infection. 
Cankers per too twigs. 
1920 
1921 
1920 wood. 
1921 wood. 
2R2. 
36 
72.4 
1*5 
400 
3 R2 . 
39 
68.8 
137 
546 
2R5 . 
15 
15 -1 
18 
54 
2R6. 
24 
4 i .3 
30 
137 
The disease was worse on all trees in 1921 than in 1920, but was 
consistently worse in the first two trees than in the others and was 
least severe in the third tree. The correlation is most striking in the 
canker infection of the two years. In 1920 the relative prevalence of 
cankers in the four trees may be expressed as 100-119-16-26 and in 
1921 as 100-136-13-34. There is a marked individuality of trees with 
regard to the severity of blotch. 
In individual trees it has been noted that cankers are much more 
prevalent in the lower than in the upper part of the tree, a condition 
which would naturally result from drip infection in a water-disseminated 
fungus of this type. In very badly diseased Northwestern trees, only 
a very few cankers could be found in the topmost branches. The 
highly susceptible watersprouts and suckers, because of their position 
in the tree, are subject to abundant infection and should of course be 
pruned out every year, as Scott and Rorer (15, p. 21) and others have 
recommended. It is impossible to prune out the cankers on bearing 
wood because of their prevalence in old trees. 
CANKERS IN YOUNG ORCHARDS 
Because of the large and increasing acreages of young commercial 
orchards in Indiana, new aspects of blotch control have developed. 
Blotch cankers have been found very commonly present in young trees 
of such varieties as Oldenburg, Transparent, and Benoni. In a block 
of trees at Vincennes, set out in 1918, 98 out of 156 Oldenburg trees, or 
63 per cent, and 53 out of 61 Transparent trees, or 88 per cent, bore 
blotch cankers. The infected trees were scattered here and there and 
almost all infection was in the form of old cankers on the trunks or 
large branches. The blotch sprays had been applied during the pre¬ 
ceding two years, so practically no young cankers had been formed. 
There was no evidence of tree-to-tree spread of the disease and all 
indications were that the original nursery stock had been infected. 
In a block of interplanted 2-year-old Ben Davis and Oldenburg 
trees, 19 out of 36 Oldenburg trees showed blotch cankers while none 
were noted on the Ben Davis trees. In the same plantation, 3-year-old 
Oldenburg trees from another source showed very little blotch. In a 
