JOURNAL OP AGRICOLTORAL RESEARCH 
Vol. XXV Washington, D. C., September 8, 1923 No. 10 
ORIGIN AND CONTROL OF APPLE-BLOTCH CANKERS 1 
By Max W. Gardner 2 
Associate in Botany, Purdue University Agricultural Experiment Station 
INTRODUCTION 
On account of the great significance of the twig cankers as a means of 
overwintering and source of early infection of the apple-blotch fungus 
(Phyllosticta solitaria E. and E-), knowledge of the mode of origin of 
these cankers is highly important. Likewise any new light on methods 
of canker prevention and eradication is much to be desired. 
The identity and significance of the blotch cankers were discovered 
about the same time by Scott and Rorer (14) 3 and by Sheldon (16) t and 
petiole lesions were described by Sheldon and later by Scott and Rorer 
(25), who made an incidental observation of peculiar interest. They 
found a large percentage of the fruit buds in an orchard of Limbertwig, 
Missouri, and Ben Davis trees in Arkansas being killed in midsummer 
and attributed this in part to the apple-blotch fungus ( 1 5, p. 11) which 
according to their observations and cultural work “ extended down from 
diseased leaf petioles into the twigs at the base of the buds, which were 
soon killed.” Apparently, no significance was attached to this phe¬ 
nomenon in connection with the origin of cankers, since they mention 
spore infection of the twigs. 
Lewis (10, p. 528,333), who studied this disease on the Missouri variety 
in Kansas, states in connection with fruit spur cankers that “the fungus 
sometimes enters from the leaf stem, and at other times through the 
new growth just below the bud/' and in connection with the importance 
of leaf infection he mentions the “possible infection of the twig from the 
petiole.” 
Roberts (. 12 , 13) was able to produce cankers on young twigs and water- 
sprouts by spraying with a water suspension of the spores, but was unable 
to infect older branches in this way and also was unable to cause infection 
of twigs by wound inoculation. These results would indicate that 
cankers are the result of germ tube infection through the uninjured 
epidermis of very young wood. 
A study of the blotch cankers on the Northwestern variety at Moores- 
ville (orchard of Mr. D. B. Johnson) and Knightstown (orchard of Mr. 
J. B. Hamer), in central Indiana, from 1919 to 1922, and on the Olden¬ 
burg variety at Mitchell, in southern Indiana, in 1921 and 1922, indicates 
that a large percentage of the cankers on twigs are the result of invasion 
from infected petioles rather than of direct spore infection (7). The 
1 Accepted for publication June 25, 1923. Contribution from the Botanical Department of Purdue 
University Agricultural Experiment Station, La Fayette, Ind. 
* The writer wishes to aclaiowledge his indebtedness to Prof. H. S. Jackson for helpful suggestions and 
to Prof. Laurenz Greene, Mr. C. E. Baker, and Mr. R. A. Simpson for their cooperation. 
* Reference is made by number (italic) to “Literature cited,” p. 417-418. 
Journal of Agricultural Research, 
Washington, D. C. 
ft£g 
Vol. XXV, No. 10 
Sept. 8, 1923 
Key No. Ind.-i2. 
60095—23-1 
( 403 ) 
