79 



cases be killed or peruiaiiently weakened. In sucli eases the branch shouUI be 

 cut off below the diseased area and burned. The use of fungicides will serve 

 to reduce the tendency towards gunnning. 



Boring in.sects of the peach, plum and cherry may also cause a flow of 

 gum from the wound made in entering, and these wounds probably often serve 

 to allow the entrance of fungi, hence the desirability of combating the insect 

 enemies of these trees. — Michigan Bulletin No. 23. 



Fire Blight (Bacillus amylovorus, Burrill. ) 



That species of blight which is sometimes called " fire blight " frequently 

 destroys trees in the fullest apparent vigour and health, in a few hours turn- 

 ing the leaves suddenly brown, as if they had passed through a hot flame, and 

 causing a morbid matter to exude from the pore.s of the bark of a black 

 fcrruf/inous appearance; this happens throughout the whole course of the 

 warm season. 



Sumptoms. 



The first indication of fire blight is .seen either in the browning and sub- 

 sequent blackening of the leaves, or of the young twigs, or of the tender 

 shoots. When the twigs or shoots are the principal parts affected the disease 

 is spoken of as twig blight. I'ears show the presence of the disease more 

 frequently by the blighting and blackening of the leafy tufts of the spurs, and 

 show 'it especially by the darkening of the blossom clusters on the 

 larger clusters, while later the branches themselves become blackened. 

 The progress of the disease is always downward, an inch or more each day, 

 depending upon the season, until the larger branches are infected. In the 

 more susceptible varieties it spreads more quickly, involving the whole tree ; 

 but in the more resistant varieties the progress of the disease is not so fast. 

 When the disease is active the bark of the diseased branches cracks, and a 

 thick, blackish, gummy fluid exudes, and later the infected bark becomes 

 hardened, dry and shrunken. The disea.se occasionally appears on the larger 

 branches and trunks of fruit trees when these have been bruised or otherwise 

 injured, when it appearance is similar to the injury known as " sunburn " or 

 •• sun-scald." This disease of the trunks or larker branches is sometimes 

 spoken of as " body blight " or " rough bark." The inner bark and cambium 

 layer of the limbs and trunk are the most important parts of the tree killed 

 by the blight. Instances are known of its attacking the fruit, producing 

 watery ulcers accomjiauied by brown discolouration and decay. The disease 

 may be known by its peculiar odour, said by some writers to resemble 

 putrefaction. 



When the disease is in progress, the discoloured blighted portion blends 

 gradually into the colour of the normal bark, but when the disease has stopped 

 there is a sharp line of demarcation between the diseased and healthy 

 portions. — (Waitc.) 



Conditions Affecting the Spread of the Disease. 



Fire blight differs in severity in different localities, and there are a 

 number of conditions which affect the character and progress of the disease. 



Every tree of the pome family is subject to the blight, but pears and 

 (piinces are more susceptible than plums and apples. The mountain ash, 



