DISEASES OF SPECIAL CROPS 101 



deaux injury. The use of too much Bordeaux, so that 

 it drips from the leaves, increases the Bordeaux injury, 

 as does also the presence of too much copper in the 

 mixture. 



PEAR 



Blight, fire blight (Bacillus amylovorus (Burr.) De Toni). 

 — The name " fire blight " is well chosen, since the affected 

 tree, with its shriveled branches and shrunken, blackened 

 twigs, gives the impression of fire injury. 



During winter the disease may best be recognized from 

 the fact that the leaves of the diseased twigs do not fall as 

 do those of healthy twigs. In the early spring, when the 

 disease is most aggressive, the blighted twigs may l^e known 

 at a glance by their dead black leaves, while on closer 

 examination the bark and wood are seen to be black and 

 dead. This blight is the worst disease of the pear and is 

 also bad on the apple, quince, and hawthorn, and to some 

 extent affects plum, apricot, and mountain ash. 



It has been known for more than a hundred years, and 

 in many cases even whole orchards have succumbed to 

 its attack. One pear grower near Washington, D.C., 

 estimated his loss from this one disease in one year at 

 $10,000. The disease is, widely known throughout the 

 United States, but is as yet confined to North America. 



So diverse and numerous were the early theories as to 

 the nature and cause of blight and so fruitless were the 

 discussions in earlier years that the western New York Hor- 

 ticultural Society passed resolutions to prohil^it further 

 reference to the subject until entirely new facts were forth- 

 coming. Among the numerous theories might be men- 



