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. (b) Throughout the summer, 
