APPLE SCAB 
Of all the diseases of the apple, this is the most common and best known 
to the growers. It is the one fungous disease for which they spray. It is 
world wide, occurring practically wherever the apple is grown. While 
there is a marked difference in the susceptibility of varieties, all will suffer 
some under conditions especially favorable to the fungus causing the 
disease. The scab of the pear is very similar in its symptoms to the apple 
scab but is caused by a distinct but closely related species of fungus. 
SYMPTOMS 
The disease affects the leaves, flowers, fruit and rarely the twigs. 
Material is provided showing the different symptoms. 
On the leaves. The first evidence of the disease in the spring is on the 
unfolding leaves. The scab-spots usually appear first on the lower surface, 
but later new spots appear on the upper surface. Examine the leaves 
provided and OBSERVE :-— 
1. The size, form and character of the spot. The radiating char- 
acter of the lesion. To what due? 
2. The character of the injury to the leaf. Does the injury show 
on the surface opposite the spot? 
3. The difference in the character of the upper and under surface 
of the leaf itself; and of the scab-spots on the two surfaces of the leaf. . 
4, The variations in the character of the scab-spots on differ- 
ent leaves. (Compare Cornell Bul. 335, pl. I.) 
Make pRawiNncs to show the characters of the scab-spots on the 
upper and under surfaces of the leaves. 
On the flowers. The disease may appear on the pedicle and calyx of 
the flower before the petals fall and may be severe enough to prevent the 
setting of the fruits. (See Cornell Bul. 335, pl. VII.) In the material 
provided, OBSERVE :— 
5. The location, form and character of the scab-spots and the 
effect on the flower. Make prawincs to show these symptoms. 
On the fruit. Where the infection of the calyx is not severe enough to 
prevent the fruit from setting, the apple as it grows shows the enlarging 
scab-spots. These become very evident as the season advances. In the 
young apples provided, OBSERVE :— 
6. The black scab-spots. Their form, size, and effect on the 
fruit. To what region on the apple are they largely confined? 
7. The felty black center of the spot. In some cases, this felt 
has disappeared and the center of the spot is hard, reddish brown and 
often cracked. Note the scab-spots on the mature apple provided. 
8. The papery rim bordering the spot; best seen in the younger 
spots. This consists of the cuticle of the apple which has been loosened by 
the fungus as it spreads out from the center of the spot. (See Cornell Bul. 335, 
pl. VI, fig. 2.) 
Make prawincs to show the points brought out in 6, 7 and 8. 
_. Sometimes these spots cause a dwarfing of the apple on the affected 
side. (See demonstration specimens.) 
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