328 



MANUAL OF FRUIT DISEASES 



fection-courts the bacteria multiply rapidly and within a 

 few days infection results. The first evidence of the disease 

 in the spring is blossom-blight, the tender tissues of the 

 blossom and of the embryo fruit being killed suddenly. The 

 bacteria in a blighting blossom are carried from it to other 

 blossoms by insects, especially bees, and so the pathogene 

 spreads through the orchard, and from one orchard to another. 



From the blossoms the 

 bacteria work their way 

 down the pedicel to the 

 spur, killing the bark 

 and causing the leaves 

 as well as the blossoms 

 to wither. The leaf- 

 tissues are not usually 

 invaded. From the 

 spur the bacteria may 

 pass to the other healthy 

 pedicels of the cluster 

 and finally enter the 

 fruit through its base. 

 Fruit-blight may also 

 arise by the bacteria 

 being deposited in 

 wounds made by the 

 curculio and other in- 

 sects (Figs. 90 and 91). The bacteria are similarly introduced 

 into the growing tips of twigs and watersprouts by aphids, twig- 

 blight resulting. Affected twigs emit the ooze which serves as a 

 source of inoculum for other twigs, shoots and blossoms. In 

 most varieties of pears, twig-infection, unless removed, is 

 inclined to continue down the main limb and even into the body 

 of the tree. Watersprouts frequently mark the center of a 

 canker, indicating the manner of entrance of the bacteria. 



FIG. 89. Oozing fire-blight canker, 

 drops of exudate. 



Note 



