Sept. 8, 1923 
Origin and Control of Apple-Blotch Cankers 
415 
at least for a few years to prevent the formation of new cankers, as 
Anderson (2, p. 26; p. 385) has recommended, and the eradication 
of the old cankers by pruning and excision. The effectiveness of the 
sprays in canker prevention has been shown, and the recommendation 
of Scott and Rorer (15) and others that cankered twigs be pruned out 
is particularly applicable in the case of young trees. 
The feasibility of canker eradication in young trees has been tested 
in cooperation with Mr. R. A. Simpson at Vincennes, Ind., and it has 
proved to be a comparatively simple process. Many cankers were 
removed by pruning out spurs and smaller limbs, and the cankers on 
the trunks and larger limbs were cut out with a sharp knife. The 
fungus does not penetrate much more than halfway through the bark 
and the diseased bark tissue can be shaved off without cutting deeply 
enough to injure the underlying cambium layer (PI. 3, A, B). A number 
of cankers were excised from Oldenburg trees in the spring of 1921 
and the wounds healed rapidly and perfectly. A few cases of marginal 
renewal of fungous growth showed that it is necessary to cut about 1 cm. 
in advance of the visible margin of the canker in order to remove all 
of the mycelium. This is particularly true at the sides since the canker 
tends rapidly to encircle the limb (PI. 3, A). It is also essential to cut 
deeply enough to remove all of the discolored tissue. 
In a block of Oldenburg and Transparent trees set out in 1918, the 
blotch cankers were removed early in April, 1922. Cankers were found 
in 58 of the 156 Oldenburg trees and from these about 59 cankered 
limbs or spurs were pruned out and 134 cankers were excised. Cankers 
were found in 48 of the 61 Transparent trees, mostly on the trunks, 
and from these trees three cankered limbs were pruned and 145 cankers 
shaved off. Since this plot had received the blotch sprays the previous 
year, very few new cankers appeared. 
Reinspections of this plot early in November and in April, 1923, 
showed that 40 per cent of the trees operated upon were free from 
cankers. The wounds had become mere surface scars in the bark and 
no injury to the trees was noticeable (PI. 3, C). A coating of melted 
paraffin had been applied to some of the wounds but proved to be 
unnecessary. However, about 300 cankers scattered among no trees 
had been overlooked and were removed. The need of more than one 
reinspection and repetition of the process is apparent. Fire blight was 
prevalent when the blotch cankers were cut out, but no cases of infection 
of the cuts were found. 
In a smaller block of 34 Oldenburg trees planted in 1920, 19 bore 
cankers and from these trees 61 cankers were removed on April 26. 
On November 9, 50 per cent of the trees operated upon were free of 
infection, but four cases of marginal renewal of fungous growth and 44 
cankers were found. Most of the latter were on 1921 wood, the result 
of a failure to apply the blotch sprays in 1921, and were not visible in 
April when the first inspection was made. This emphasizes further the 
necessity of a reinspection to detect cankers overlooked or invisible at 
the time of the first operation. 
In an orchard near Paoli, Ind., 27 out of a group of 55 young Rome 
trees contained cankers and from these trees 23 cankered limbs were 
pruned and 75 cankers were shaved off. In a block of 24 Transparent 
trees about 10 years old, 20 bore cankers and from these trees 92 can¬ 
kered limbs were pruned and 116 cankers excised. By fall these ex¬ 
cision wounds were mere scars in the bark. 
