330 MANUAL OF FRUIT DISEASES 



seminating agents, such as aphids. Should no frost occur and 

 were the spring backward, the insects would multiply rapidly 

 while blossoming would be retarded, hence at blossoming large 

 numbers of insects are at hand to disseminate the bacteria 

 rapidly. During the growing-period, immediately following 

 blossoming, should the weather become hot and dry, the rapid 

 growth is checked and the otherwise succulent tips become 

 harder and more woody. Such shoots are less liable to blight- 

 infection. On the contrary, muggy periods favor the disease 

 in that the tissues become gorged with sap and thus offer less 

 resistance to the invading bacteria. 



Control of fire-blight. 



In attempting to control fire-blight, the following important 

 points should be borne in mind : (1) that the disease is caused 

 by bacteria which gain entrance to the host tissues only through 

 wounds, or punctures by insects, into succulent, rapidly growing 

 tissues, or through the nectaries of the blossoms. (2) That 

 insects of several kinds are the usual agents of inoculation. 

 (3) That practically all pome fruit-growing sections in North 

 America are infested, and therefore there is always a source 

 from which the bacteria may be disseminated. (4) That all 

 known varieties of the hosts, on which the blight-organism 

 occurs, are more or less susceptible; while some show resist- 

 ance, none are wholly immune. Therefore control consists 

 chiefly in the elimination of the pathogene from the infected 

 trees. This is accomplished by a strict application of the 

 following operations : (a) inspect all pear trees in the autumn 

 and again in the early spring before the blossoms open, and cut 

 out and treat all cankers in the body and main limbs. With 

 a sharp knife, or draw-shave, remove all the diseased tissue, 

 wash the wound with corrosive sublimate (one tablet to one 

 pint of water), and, when dry, paint the wound with coal-tar 

 or lead paint, preferably the former. The wound-dressing will 

 need renewal every year or so. (6) Throughout the summer, 



