62 Diseases of Economic Plants 



marizes the results of observation covering six y(>ars in 

 Illinois as follows: 



"It may be safely concliKUHl that moist weather with a 

 considerable precipitation and a high temperature are 

 favorable to the spread and growth of bitter-rot. There was 

 no opportunity to note the effect of moist, cold weather 

 though it might be argued from analogy, there being no 

 evidence of the disease in northern and very little in central 

 Illinois, where the rainfall is abundant and the mean tempera- 

 ture lower, that moisture without high temperature is not 

 favorable to the development of the disease. Hot weather 

 alone unaccompanied by moisture proved unfavorable to 

 the spread of the disease, as seen in the season of 1901, 

 but hot weather alone did not prevent the disease from 

 accomplishing its work of destruction after infection had 

 once occurred, as was observed in 1900 when the dry month 

 of August followed the abnormally wet months of June 

 and July." 



The spraying schedule should be adjusted to meet the 

 weather conditions. Rainy weather not only provides 

 favorable conditions for infection but removes the protecting 

 spray. ^ 



\ 



PEAR ■'^'■ 



■ Fire-blight, blight '•''~'^' ^^-^ {Bacillus amylovorus (Burr.) 

 Trev.)."— 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 

 the winter diseased twigs may be recognized by the dead, 

 shriveled leaves still clinging to them. In the early spring, 

 these leaves still persist, while on closer examination the 

 bark and wood of the blighted twigs are seen to be black 

 and dead. This blight is the most important disease of 

 the pear and is also serious on the apple, quince, and haw- 

 thorn, and to some extent it affects plum, apricot, and 

 mountain ash. 



