BLACK ROT CANKER OF APPLE 
This disease affects chiefly the apple, but other pomaceous fruits are 
by no means free fron the trouble. Marked variation in susceptibility. 
of varieties is shown only where the canker-form of the disease appears. 
In western New York the Twenty Ounce is noted for its susceptibility 
to the canker. As a fungous disease of the apple in this state, it is perhaps 
second only to apple scab, the chief losses occurring as a result of cankers 
on the large limbs. 
SYMPTOMS 
Lesions appear on limbs, leaves and fruit, known on each respectively, 
as cankers, leaf-spots and black rot. ; 
On the limbs. Larger limbs are more often affected than twigs or 
trunks. The lesions are cankers and are usually on the upper sides of the 
limbs. At first the bark is reddish brown in color and sunken. (See Cor- 
nell Bul. 379 : 62-68, pl. VIII, and IX, fig. 4). Study the specimens 
available and OBSERVE :— 
1. The size of the lesion; its surface, appearance, shape, color 
and margin. Is the margin definite? 
2. The pimple-like fruit-bodies of the pathogene; their numbers 
and distribution within the lesion-area. Supplement the above with a care- 
ful study of the illustrations in Cornell Bul. 379 to show the characters of 
the cankers. 
On the leaves. The first evidence of a spot on the-leaf is the appearance 
of a minute purplish speck which soon enlarges until it has reached a 
diametér of 2 to 10 millimeters. It then becomes brown. Examine the 
the specimens provided and oBsERVE:— 
3. That the spots are at first circular, but that older ones show 
a lobing or a concentric appearance due to secondary spreading; the center 
appears lighter in color and the whole effect is that of a frog’s eye. The 
disease is therefore called ‘‘frog-eye”’ by certain writers. 
4. The presence or absence of the fruit-bodies of the pathogene. 
If present they will be much smaller than those on the cankers. 
Study, in addition to the specimens, the illustrations in Cornell Bul. 379, 
pl. VII, fig. 3; Virginia Bul. 209; Pl. Ind. Bur. Bul. 121, pl. III, fig. 1-2. 
Defoliation results in cases of severe infection. (See last named bulletin, 
plate IV.) . 
On the fruit. Black rot is primarily a rot of ripe fruit, although green 
fruits may be attacked. Symptoms may show anywhere on the surface. 
Study, the material and illustration specimen provided. OBSERVE:— 
5. That the lesions appear first as small brown spots, which may 
turn dark at once or remain brown until the entire fruit is involved. 
6. Concentric color-zones in the lesion. 
7. The firmness of the rotted tissues; taste and odor. 
. 8. The black fruit-bodies of the pathogene just under the 
skin; their distribution and arrangement within the lesion. 
DRAW to show the characters brought out above. (See Cornell Bul. 
379, pl. VII, fig. 1-2.) 
The lesion usually surrounds an injury of some sort, as for EXAMPLE :-— 
. _ 9. A codling-moth wound in either green or ripe fruits, as seen 
in the illustration specimens. pRaw. 
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