404 
Journal of Agricultural Research voi. xxv, No. 10 
evidence and the obvious deductions are presented herein together with 
an account of the spray control of canker formation and the eradication 
of cankers in young orchards. 
LOCATION OF CANKERS 
One of the outstanding features of the blotch disease in Indiana 
is that a very high percentage of the cankers on the bearing wood are 
located at leaf scars (PI. i, C, D, F). This condition is very evident on 
wood not over 3 or 4 years old, but even the older cankers are generally 
located at leaf nodes and crotches or about the bases of spurs that have 
developed from dormant buds (PI. 3, A). 
In September, 1921, records taken on 632 cankers on 1920 wood of 
the lower limbs of Northwestern trees showed that 624, or 98 per cent, 
were located at leaf scars, and in the fall of 1922 records taken on 967 
cankers on 1921 wood of the same trees showed that 963, or 99.5 per 
cent, were located at leaf scars. Observations made in October, 1921, 
on 187 Oldenburg twigs of the current season showed that out of 129 
small cankers which had already appeared 61 per cent were located at 
leaf scars, 16 per cent at the bases of terminal bud scales, and 23 per 
cent between the scars. Observations made in July, 1922, on the 1921 
wood of 80 Oldenburg twigs showed that out of 553 cankers noted 87 
per cent were at leaf scars, 5 per cent at the bases of terminal bud scales 
(PI. 1, A), and 8 per cent between leaf scars. 
On suckers, watersprouts, seedlings, and nursery stock a considerable 
proportion of the cankers occur between the leaf scars (PI. 1, B). Counts 
made on watersprouts showed that 44 out of 50 bore cankers between the 
leaf scars on growth of the current season. Counts made on suckers of 
the current season showed that out of 92 lesions noted, 58 per cent were 
between the scars. On the first-year scion wood of 10 nursery 
trees 159 blotch cankers were counted, and 58 per cent of these occurred 
between the leaf scars and the remainder at the scars (PI. 1, E). It 
would seem, therefore, that on rapidly growing wood cankers may occur 
rather generally between the leaf scars. 
With respect to location there are four types of canker, (1) at the leaf 
scars, (2) at the bases of terminal bud scales, (3) at the bases of spurs, and 
(4) between the leaf scars. Of these the first is the prevalent type on 
bearing wood and consequently the most important. 
DATE OF APPEARANCE OF CANKERS 
Since Roberts (12) found only young twigs susceptible to spore infec¬ 
tion, and since the infection period is early in the season, cankers result¬ 
ing from direct spore infection should become visible during the first sea¬ 
son. This has proved to be the case. The cankers between the leaf scars 
may be seen the first season and these undoubtedly result from direct 
spore infection. But in central Indiana the cankers at the leaf scars, 
which are the prevalent type on bearing wood, do not as a rule become 
visible until the following spring. It should be noted, however, that 
in southern Indiana, a larger percentage appear the first season than 
in the central part of the State. 
In the fall of 1920, 35 twigs of 1920 wood on a badly cankered North¬ 
western tree at Mooresville were tagged and carefully examined. Three 
small cankers at leaf scars and three cankers between leaf scars were 
visible. No more of the latter type were evident. On March 22, 1921, 
