BLIGHT OF THE PEAR AND APPLE. 293 



BLIGHT OF THE PEAR AND APPLE. 



L. F. HENDERSON, BOTANIST, AGRICULTURAL EXPERIMENT STATION, 



MOSCOW, IDAHO. 



(Extract from Bulletin.) 



Though this trouble has been known as working" havoc with or- 

 chards for a century or more, it is only in comparatively recent times 

 that its true nature has been understood. For a long period of years 

 the discussions of this trouble were of such a theoretic nature that 

 many horticultural societies forbade its being brought up in their 

 meetings, unless some one had something of absolute knowledge to 

 offer about it. Various causes were ascribed for its presence, such 

 as "sour sap," "atmospheric conditions," "soil conditions" and "ef- 

 fects of various fungi." In 1878, however, Professor Burrill, of Il- 

 linois, discovered the true cause and announced his discovery to the 

 world. This was found to be a bacterial disease, due to the presence 

 of myriads of little germs in the inner bark and cambium. The 

 germ was called by Prof. Burrill Micrococcus amylovorus from the 

 eagerness with which it seizes upon and devours the starch in these 

 tissues. From the subsequent studies of Arthur, at the Geneva 

 Station, in New York, and of Waite, in the U. S. Department of Agri- 

 culture, we know how this germ or bacterium lives, reproduces itself 

 and is carried from tree to tree. 



Luckily the disease is a very conspicuous one, which renders 

 its presence in an orchard the more inexcusable when well known. 

 It affects twigs, leaves, young fruit and the branches or trunks. 

 From the experiments of Waite it has been found that it cannot at- 

 tack the plant through the uninjured bark or leaf. It can, however, 

 gain entrance through any injured place on trunk, limb or even leaf. 

 Its most common points of entrance are natural ones. These are 

 the young growing tips of the branch, the stigma of the flower, or 

 the glands which secrete nectar. Therefore the "flower-blight," the 

 "twig-blight" and the "branch or trunk blight" are all forms of this 

 disease. 



In the first, the young twig, especially if it be growing rapidly, 

 turns black in both leaf and stem, and wherever the leaves are 

 blighted they remain black and dead through the ensuing winter. 

 This black, piratical flag is the surest evidence of its presence. 



In the "flower-blight" a whole bunch of flowers, or frequently 

 every bunch on the tree, will be affected, and dying back to the be- 

 ginning of the spur hold the blackened flowers and young fruit 

 through the entire year. This is the most common form on the 

 apple. 



