FIRE-BLIGHT OF APPLE, PEAR, ETC. : TRANSMISSION 385 



art (1915) showed that it may enter through wounds made by 

 hailstones (compare with No. XIII and XIV). 



The disease is probably carried sometimes on nursery stock, 

 but not often, I think, owing to the fact that it dies out rather 

 quickly in the dead shoots. Probably this fact also accounts for 

 its not having been introduced into other parts of the world, if we 

 may assume, as seems probable, that the eastern United States 

 is the original home of the disease, and that it has not occurred 

 until recently in any other pear or apple-growing region of the 

 world. Was it introduced into Japan from the United States? 



Eradication of the Disease 



Complete freedom from fire-bhght may never be hoped for, 

 any more than from any other widespread and highly infectious 

 disease, but there are certain palliatives which if properly applied 

 will reduce its destructiveness to insignificant proportions. 

 These fall into two main categories: (1) tree surgery; (2) resis- 

 tant varieties, or rather immune stocks for sensitive varieties, 

 since the latter include all our fine/ sorts of pears and apples, 

 the discarding of which is not to be thought of. 



It has been demonstrated conclusively by Waite and others 

 that the spring blight is distributed principally by bees and other 

 insects which obtain the infection from oozing patches of ' ' hold- 

 over" bhght. In the control of this chsease it is, therefore, of 

 prime importance to search the trunks, limbs and roots in late 

 autumn or winter and remove all blighted spots. Such removal 

 is equally important if the blight is wind-distributed, as main- 

 tained by Stevens and his associates (Science N.S., Vol. XLVIII, 

 pp. 449-450). If this is done thoroughly over a wide area there 

 will be very little spring-blight. 



If the eradication of the canker, or hold-over bhght, has been 

 neglected the next best thing is to cut out the spring- and summer- 

 blight thoroughly as fast as it appears, including the neglected 

 cankers, disinfecting the tools from limb to limb and tree to 

 tree, since if you neglect this you will inevitably distribute the 

 bacteria by means of your saw, gouge, knife and p uning shears. 

 Both tools and tree-wounds should be disinfected. Mercuric 



