SOME BACTERIAL DISEASES OF PLANTS. 129 



It will be safer if they are from a crop in which no blight appeared 

 at all. 



The Control of Bacterial Diseases in General. 



It may be said that almost without exception spraying is of little 

 or no value in preventing diseases of plants caused by bacteria. 

 We must look to other means of preventing or controlling their 

 ravages. As is the case with bacterial diseases of man and other 

 animals, the first thing to do is to remove if possible the source of 

 infection. Usually if the annual history of the disease is fully 

 understood this is a relatively easy matter. When the disease 

 appears in a crop it is often possible to do much toward its control 

 by promptly removing and destroying all diseased plants. Even if 

 the crop is a total loss all the diseased plants should be burned and 

 every effort made to put the land in as sanitary a condition as 

 possible. Avoid the planting of susceptible crops on lands known 

 to be infected. The elimination or control of the common carriers 

 of infection is also an important precaution. Reject seed known to 

 be from infected lands or localities. Destroy insects that are re- 

 sponsible for the spread of the bacteria from plant to plant. And, 

 lastly, what is coming to be perhaps most important of all grow 

 varieties resistant to the disease. 



Discussion. 



In answer to the question "Does the fire blight attack plum trees ?" 

 the lecturer stated that the fire blight sometimes appears on the 

 plum and the efi"ect is the same as on the pear but more destructive. 

 The blight is not common on the plum but occasionally appears. 



^^'illiam H. Spooner asked if there were not some kinds of pear 

 trees that were not affected by the blight. He had noticed in his 

 orchard that the Superfin pear was the only one onwdiich it appeared. 



Prof. Whetzel replied that the fire blight attacks all varieties, 

 but it was much less frequent in orchards along lake fronts and 

 along the seashore than in inland regions. It seems to be less 

 common on trees growing in sod. 



