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PEARS, APPLES, and QUINCES 



Blight, sometimes called fire blight or pear 

 blight, is a common and destructive bacterial 

 disease of pears and quinces. Blight attacks apples, 

 too, and sometimes damages ornamental plant- 

 ings of hawthorn, spirea, pyracantha, flowering 

 almond, and mountain ash. 



Blight attacks (1) blossoms and young fruits, 

 causing them to blacken and die; (2) tender tips 

 of twigs and water sprouts, often killing back 

 the twigs for a foot or more and causing leaves 

 to turn black; (3) spurs, large branches, trunk, 

 collar (base of the tree), and roots. In a single 

 season, blight can severely damage — or kill — the 

 tree it attacks. 



Blight usually appears first when fruit trees 

 are in blossom and stays active until rapid spring 

 growth stops (about a month after blooming). 

 Don't prune or fertilize your fruit trees too heav- 

 ily during this time. These practices may stimu- 

 late the trees to put out succulent growth, which 

 is extremely susceptible to blight. 



Blight of pears 



Blight is so destructive to Bartlett, Clapp 

 Favorite, Bosc, Flemish Beauty, and other high- 

 quality pears, that these varieties can be commer- 

 cially grown in only a few favored localities. 

 In fact, most of our marketed pears are 

 grown in three States — California, Oregon, and 

 Washington. 



Blight of apples 



Blight sometimes damages blossom clusters and 

 young shoots of such susceptible apple varieties 



as Jonathan, Yellow Transparent, Wealthy, and 

 Transcendent Crab. Although blight is especially 

 destructive in some seasons, it seldom is serious 

 enough to prevent, commercial apple production. 



Blight of quinces 



Quince trees are as susceptible to blight as the 

 most susceptible pear varieties. Although quinces 

 are not commercially important in this country, 

 small quantities of them are grown for processing 

 into jams and jellies. 



HOW BLIGHT SPREADS 



Bacteria that cause blight in the spring usually 

 overwinter in cankers in the bark of large 

 branches, trunks, or roots of trees attacked the 

 previous year. Occasionally they overwinter in 

 twigs or small branches. 



Pollinating insects, especially honey bees, play 

 a major role in spreading fire blight bacteria dur- 

 ing the early growing season. From blight cankers, 

 the bacteria are carried to open blossoms, and from 

 blossoms to other trees. Other insects that come 

 in contact with the bacteria also help spread the 

 disease. Insects, and probably rain, to some extent, 

 carry bacteria from blossoms to twigs and water 

 sprouts. 



Usually hot, dry summer weather and the ac- 

 companying hardening of tree tissues prevent new 

 blight infections, while helping old ones to die 

 out. Sometimes, however, blight bacteria are so 

 favorably situated in thick bark they do not dry 

 out and are able to persist in holdover cankers. 



