Blight rf 



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 

 plantings 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 heavily during this time. These prac- 

 tices may stimulate the trees to put out succu- 

 lent 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 

 commercially grown in only a few favored lo- 

 calities. In fact, most of our marketed pears 

 are grown in three States — California, Oregon, 

 and Washington — where the humidity is low. 

 The introduction of overhead irrigation in- 

 creases the spread of fire blight even in these 

 localities. Such varieties as Magness, Moon- 

 glow, and Seckel are somewhat resistant to 

 blight. The Kieffer variety is also quite resist- 

 ant but it has poor fruit quality. 



Blight of apples 



Blight sometimes damages blossom clusters 

 and young shoots on such susceptible apple 

 varieties as Jonathan, Yellow Transparent, 

 and Wealthy, but it seldom is serious enough to 

 prevent commercial apple production. Red De- 

 licious, Golden Delicious, and Mcintosh have 

 resistance. 



Blight of quinces 



Quince trees are very susceptible to blight. 

 Small quantities are grown in this country for 

 processing into jams and jellies. There are no 

 blight resistant varieties. 



HOW BLIGHT SPREADS 



Bacteria that cause blight in the spring usu- 

 ally 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. 



From blight cankers, the bacteria may spread 

 to open blossoms, and from blossoms to other 

 trees. Insects that come in contact with the 

 bacteria also help spread the disease. Insects, 

 and probably rain, to some extent, carry bac- 

 teria 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. 



