8 



Climatic conditions influence the disease; warm, moist weather with 

 much rain favour it, whilst bright, dry, sunny weather tends to check it. 



High cultivation, rich soil, heavy manuring, free use of fertilizers' 

 heavy pruning, or any other treatment which has a tendency to in- 

 duce new and succulent growth, favors the disease, as the bacteria 

 grow with far greater rapidity and penetrate more quickly from cell 

 to cell when the tissues are gorged with sap. Insects are more partial 

 to young succulent shoots and leaves, and the bites and punctures of 

 such insects whose mouth parts may be contaminated with pear 

 blight germs often serve to infect the tree. 



It is thus manifest that healthy, thrifty, vigorous, well fed and 

 well cultivated trees are more liable to the disease than others, and 

 hence the severity of an attack of fire blight may be lessened by con- 

 ditions which are under the control of the grower. 



Treatment. The treatment of fire blight is of two kinds — that 

 which is designed to put the tree in a condition to withstand the 

 attack of the blight microbe, and those methods which aim at the 

 extermination of the causal bacterium. Unfortunately all methods 

 which are used for hindering the attack of the microbe consist of 

 restraining the full development of the tree, and hence any such 

 system of procedure should not be followed unless an orchard is very 

 badly attacked 



High cultivation with pruning and the other conditions already 

 mentioned as predisposing trees to blight should be avoided, but the 

 trees should be allowed to ripen the wood, and in order to do this the 

 fruit grower must use any method which will check the amount of 

 moisture in the soil — for instance, by the growth of a clover crop. 



The tire blight organism cannot be exterminated by spraying, as 

 the microbe lives in the tissues beneath the outer bark, and it is im- 

 possible to reach it with any spraying solution, for, unless the bacteria 

 come into contact with the germicide, spraying is ineffectual. 



There is, therefore, but one remedy, to cut out and burn the 

 affected parts of the tree. It is very necessary when cutting out a 

 diseased branch or twig to cut well below the discolored portion, as 

 the bacteria are in most cases far below the discolored portion, the 

 discoloration not being produced immediately upon the appearance of 

 a few bacteria, so that if only the discolored portion were cut oft 

 numbers of bacteria would still be left in the stump, and these would 

 continue to multiply, and the disease would soon be evident again. 



Cutting of affected parts may be done at any time in the winter 



