44 PROTECTION OF PLANTS, 1915-16 



after a very short time the delicate shoot begins to have a water-soaked 

 appearance and becomes filled with a thick whitish fluid. Gradually the 

 twigs turn brown and small beads of exudate appear which are white at 

 first, but soon turn to a dark amber. The disease then enters the leaves 

 causing them to turn brown and dry. They do not fall to the ground, 

 but remain on the tree long into the winter. When the disease spreads 

 downward into the more matured wood below, the bark wrinkles, and turns 

 brown and finally black. The cambium is saturated with moisture and 

 streaked with red. When the weather is warm and the tree is growing 

 fast the disease spreads very rapidly. 



Blossom Blight. 



The bacteria gain their easiest access to the plant through the blossoms. 

 The first indication of blossom blight is detected about two weeks after 

 the blossoming season. The flower clusters are seen to turn gradually 

 brown and shrivel up. The small immature fruit begins to take on a water- 

 soaked appearance and seems to be filled with whitish juice formed by the 

 bacteria. Gradually it commences to blacken and the disease can be seen 

 working its way down the slender peduncle from which numerous beads of 

 exudate emerge. Sometimes, chiefly on apple trees, the disease only enters 

 the fruit spur and then dies off. But if it is the right variety of pear tree, 

 and growing conditions are good, it often enters the branches. Blossom 

 Blight is probably the most dangerous form of the disease. 



Fruit Blight. 



This form is rot so important. Immature fruits are more generally 

 attacked than mature ones. The disease may either enter the fruit by 

 the peduncle from a diseased twig or by way of punctures through the 

 skin. The flesh becomes spong>' and shows large amounts of brownish 

 exudate. The skin becomes deeply wrinkled and the fruit does not fall off. 



Life Cycle of Fire Blight. 



The disease passes the winter in the form of bacteria which lie along 

 the advancing margin of the diseased portions, in the fleshy bark and cam- 

 bium. This is known as " Hold Over Blight." In the spring, with the rising 

 of the sap, the organisms become active, and produce a large amount of 

 sticky liquid, which exudes in drops through the bark. This exudate, 

 white and thin at first, becomes, after having been exposed to the air, a 

 light brown or amber color, quite rubbery and almost hard in texture. This 

 exudate usually appears shortly before the blossoms open, and attracts 



