334 The Spraying of Plants. 



and eventually destroy large areas (Fig. 69). The leaves finally 

 fall to the ground, and if the fungus is very prevalent the trees 

 may be entirely defoliated. Upon the stems the affected parts 

 appear black and dead. The fruit first shows reddish spots 

 which later turn dark (Fig. 70). If the pears are attacked 

 while small, the diseased parts grow but slowly, the tissues 

 become hard and corky, and the result is an irregular fruit, 

 generally cracked upon the dwarfed side, and more or less 

 marked by isolated spots which appeared after the first seri- 

 ous infection. Quinces suffer in the same manner, but the 



FIG. 70. The fruit spot of pears. 



foliage frequently turns yellow before falling to the ground, 

 and the affected fruit is mottled with black spots less than an 

 eighth of an inch in diameter, when late infections have taken 

 place. This fungus is probably the most serious of those which 

 work upon these fruits, but fortunately it may be controlled 

 with comparative ease. 



There is a bacterial disease which is frequently mistaken for 

 the leaf blight, but it is entirely distinct. It is commonly known 

 as " fire blight " or " twig blight." It is very serious upon pears 

 and quinces, and also frequently attacks some varieties of apples. 

 It causes the foliage to turn to a uniform brown, the change 

 taking place sometimes in two or three days. The leaves do not 



