PLANT DISEASES. 249 



leaves when the buds burst, and so finally to the form- 

 ing fruit. Scab can be prevented if the young leaves 

 and fruit are protected with a coating of a good fungi- 

 cide, such as Bordeaux mixture, or commercial lime- 

 sulphur wash diluted i in 30. The first spraying 

 should be made just before the blossoms open; the 

 second, just as the petals fall; and the third, ten days 

 or two weeks later. 



Pear Scab. This disease is caused by a fungus much 

 like the one causing apple scab. The spots on the 

 pear have the appearance of sooty blotches; and when 

 badly infected the fruit cracks. The fungus lives 

 over winter on infected leaves or twigs. It can be 

 controlled by three sprayings with Bordeaux mixture, 

 just as for the apple scab. 



Pear Blight. The name fire blight is often used 

 because of the scorched appearance of affected twigs. 

 On these the leaves blacken and die early in the season, 

 but do not fall. The disease is caused by bacteria. 

 These live over from season to season in the affected 

 larger limbs, between the bark and wood. In spring, 

 as the sap rises, drops of milky, sticky fluid containing 

 myriads of bacteria ooze out from cracks at the boun- 

 dary between dead and sound bark. Insects readily 

 carry these bacteria on their bodies, and so spread in- 

 fection. Bacteria carried in this way to pear blos- 

 soms multiply very rapidly in the nectar, and work 

 down through the flower stalk and fruit spur to the 

 limb. In time they may girdle a large limb, killing it 

 by destroying the growing tissue between the bark and 

 wood. All affected twigs and small limbs should be 

 cut away and destroyed; cankers on larger limbs should 

 be cut out; large wounds should be disinfected with cor- 

 rosive sublimate solution, one part in 1,000 parts of 

 water, and afterwards painted. Culture that induces 

 rapid, succulent growth should be avoided. Fruit 

 spurs should be confined to the smaller limbs, which 

 can be removed, in case of infection, with least loss to 

 the tree. Because of the protected position of the bac- 

 teria spraying is of little value. 



