114 THE PEARS OF NEW YORK 
Scab (Venturia pyrina Aderh.), after blight, is the best-known and 
most prevalent disease of the pear in New York. Like blight, it is found 
wherever pears are grown in North America, and also wherever pears are 
grown in foreign countries. It attacks the pear at all ages from the youngest 
to the oldest plant. Twigs, leaves, flowers, and fruit suffer. A closely 
related and very similar fungus attacks the apple and causes the apple- 
scab, but the two fungi are not the same and do not spread from the one 
fruit to the other. 
The name describes the disease at maturity so that all may know it. 
Black, canker-like lesions spot the fruit, leaf, and twig. These are most 
characteristic on the pear. The scabs first appear on the fruit as olive- 
green velvety spots; the young fruits may drop; if they persist, growth 
may cease, the skin crack, or the fruit be distorted; the fruit-stalk is often 
shriveled. The scab shows on the leaves much as on the fruit and usually 
attacks the lower surface. On the twigs the scab is not so conspicuous, 
but appears as a small round spot which may or may not slough off and be 
replaced by healthy bark. Young twigs are most often attacked, in which 
case the scabby spots suggest scale insects. 
Pear-scab is caused by a fungus. The chief life events of this fungus 
must be known to control the disease. The organism passes the winter 
in leaves on the ground. In the spring, the spores which have matured 
in the spore-cases are forcibly discharged, and, being very light, are carried 
hither and thither by the wind so that some of them reach the opening 
flower and leaf-buds. If moisture and heat are sufficient, the spores ger- 
minate, and an infection is started. A foothold secured, the germ-tubes 
branch and form a dense mycelium —the velvety layer visible to the 
unaided eye. From these masses of mycelium spore-stalks arise in great 
numbers bearing countless spores which by one agent and another are 
carried to other leaves, twigs, or blossoms for new infections. New infec- 
tions continue throughout the growing season. The black scab spots on 
fruit and leaf are corky layers of tissue formed to heal the wounds made 
by the fungus which has ceased to grow vigorously in these scabs. The 
fungus may pass the winter on the twigs as well as in fallen leaves. 
Different varieties resist the scab-fungus differently. Flemish Beauty 
and Summer Doyenné are most susceptible and in seasons favorable to 
the fungus seldom present fruits with a clean cheek no matter how careful 
the treatment. Pruning off badly infected twigs and plowing under scabby 
leaves are good sanitary measures. In New York, two applications of 
