Blister Canker 
7 
In 1912 Gloyer^o of Ohio published a circular on "Blister 
Canker" caused by Nummularia discreta, but added little of 
any importance to the facts already published. 
The disease was first noted in Nebraska about 1903 but it 
received no attention and no report was made except to men- 
tion its presence in the State. 
SYMPTOMS AND GENERAL APPEARANCE 
It is impossible to describe the symptoms of blister canker 
so that the casual observer will be able to identify the disease 
in all cases. Under certain conditions the symptoms are very 
marked and characteristic, as indicated by Hasselbring^^, but 
under other conditions these characteristic symptoms are 
wanting. The injury often resembles very closely that caused 
by other agencies such as winter injury, sun scald, blight, 
collar rot, and the so-called arsenical poisoning. The writer 
is of the opinion that a large share of the damage attributed to 
other causes is in reality caused by Nummularia discreta. The 
symptoms vary with the variety of trees, point of inoculation, 
soil conditions, amount of precipitation, general weather con- 
ditions, and treatment of the orchard. On the more resistant 
varieties sharply defined cankers usually appear. In the ear- 
liest stage the bark takes on a darker brown color and soon 
becomes slightly shrunken, and depressed below the adjoining 
healthy bark. The canker usually does not begin at one small 
point and spread, but a considerable area of affected bark will 
appear rather suddenly and continue to grow in size, spread- 
ing most rapidly in the direction of the long axis of the limb. 
The initial spots vary in size, being anywhere from two to 
eighteen or more inches long and one-half to six inches wide. 
The inner bark in these spots and at the edges of old cankers 
has a mottled appearance due to intermingling of dead areas 
within the living tissues. The size of the original cankered 
spot and the mottled appearance of recently affected areas are 
due to the fact that the fungus invades the older xylem tissues 
of the tree first and then works gradually toward the surface, 
killing the tissues as it advances. The advance is naturally 
more rapid in certain portions of the affected area than in 
others. Consequently the bark is not attacked evenly, but in 
spots wherever the fungus has approached near enough to the 
surface to kill the cambium. The bark is never attacked until 
the underlying tissues are killed. 
During the months of July, August, and September small 
round blister-like protuberances one-eighth to one-quarter 
