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 Doyenne 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 



