Sept. 8 , 1933 
Origin and Control of Apple-Blotch Cankers 
409 
age of the canker was about the same as that of the wood. Spore¬ 
bearing pycnidia were found in the margins of the cankers on the limbs 
7 and 8 years old, and it is apparent that the fungus may remain active 
in the cankers many years. Anderson (j, p. 389) has recently reported 
similar findings in Illinois. 
SPRAY CONTROL OF LEAF AND TWIG INFECTION 
By means of spray tests conducted primarily for a study of control of 
fruit infection and carried out in cooperation with Laurenz Greene and 
C. E. Baker, of the Purdue University Agricultural Experiment Station, 
and with certain orchardists, the effect of the blotch sprays upon petiole 
and twig infection has been ascertained. The control of leaf infection 
was determined by counts made in the fall at the time of harvesting the 
apples, but the effect upon canker formation could not be determined 
until a year later. A more complete account of these spray tests has 
been published in a station bulletin (7). 
Considerable interest has been aroused among growers in the possi¬ 
bility of controlling blotch by means of dormant sprays of concentrated 
strength such as lime sulphur, 1 to 3. Cultural tests made in 1919 
showed that the spores already present in the pycnidia were killed by a 
dormant spray of lime sulphur, 1 to 3. Guba (9) in Illinois likewise 
found that the spores in the pycnidia were killed by lime sulphur, 1 to 3, 
1 to 5,1 to 6, and 1 to 8, as well as by copper sulphate, 1 to 6, but observed 
that the cankers continued to enlarge and produce spores. Extensive 
field tests in Indiana have shown that dormant sprays have no effect 
whatever on subsequent leaf infection and canker formation. 
The failure of dormant sprays to prevent the development of cankers 
from infection already present in the leaf scars is shown by the data 
in Table II, obtained on Northwestern trees at Knightstown. The 
sprays were applied in the spring of 1921 and the canker counts were 
made on the 1920 wood. 
None of the dormant applications prevented the development of 
cankers on the sprayed twigs. That dormant sprays have no influence 
on subsequent leaf and twig infection is shown in the data included in 
Tables III and V. 
The effect of blotch sprays applied two, four, and six weeks after 
petal-fall in 1920 upon leaf and twig infection in Northwestern trees is 
shown in Table III. The data on twig infection were obtained the fol¬ 
lowing year. All except the first two trees received a dormant spray 
of lime sulphur, 1 to 8. 
Table II .—Effect of dormant sprays on canker development 
Tree. 
Dormant spray. 
Twig infection. 
Number 
examined. 
Percentage 
infected. 
Cankers per 
100 twigs. 
2R5. 
3R2. 
2R2. 
2R6. 
Lime sulphur, 1 to8... 
Lime sulphur, 1 to 3.. 
Lime sulphur, 1 to3. 
Copper sulphate, 1 to 200. 
103 
112 
102 
142 
14. 6 
61.6 
62.8 
21. 9 
18. 4 
137*0 
IlC O 
3 °* 3 
