12 THE CONTROL OF APPLE BITTER-ROT. 



funo'us i.s spread from tree to tree and from orchard to orchard. It 

 seems, however, that the mummied fruit and the limli cankers are both 

 instrumental in carry ino' the fungus over wintei' and starting the 

 annual infection, and that insects pla^^ an important role in the spread 

 of the spores. 



During the season of 1908 and again in 1905 the writer visited a 

 number of infected orchards in Virginia and West Virginia, making- 

 special observations upon this problem. The results lead to the con- 

 clusion that the overwintering numimies hanging on the trees consti- 

 tute the chief source of infection, at least in this particular region. In 

 the majority of cases examined a mummy could be found in the upper 

 portion of the infected area, but in no case was there found associated 

 with such outbreaks an}' cankers that could be identified as bitter-rot 

 cankers. However, from observations made in the Middle West, Bur- 

 rill and Blair ^' and von Schrenk and Spaulding '' conclude that the 

 canker is the chief source of early infection, the fungus being held over 

 winter in the diseased limbs and producing spores for the infection of 

 the new crop of apples. Hasselbring'' demonstrated that the fungus 

 of bitter-rot remains alive over winter in the mummied apples. It 

 seems possible that the mature spore form of the fungus discovered 

 by Clinton may develop the following spring in the mummied fruits, 

 starting the infection on the new crop. 



After one apple on a tree becomes diseased and begins to produce 

 spores, further infections may readily take place through the medium 

 of raindrops which splash the spores to adjacent fruits, and heavy 

 dews may wash the spores to the apples below. Insects are also 

 undoubtedly instrumental in disseminating the disease,'' and they are 

 possibly the chief carriers of the spores from tree to tree. On the 

 other hand the rapidit}' with which the disease frequently spreads over 

 an orchard, practically destroying the entire crop within a few da3"s, 

 suggests the idea that, the spores are carried on the wind, and indeed 

 they seem to be onuj'present in the bitter-rot districts, only awaiting 

 suitable weather conditions. But the spore masses being sticky when 

 wet and glued to the skin of the apple when dry, there seems to be 

 little or no chance for the wind to carry the spores. 



INFLUENCIN(i CONDITIONS. 



WEATHER. 



The predominating conditions that influence the development of 

 bitter-rot are temperature and humidit3\ A few da^s of hot shower}'^ 



n Bui. 77, 111. Agr. Exp. Rta., p. 356. 1902. 



''Bnl. 44, Bureau of Plant Industry, I'. S. Department of Agriculture, 1903, pp. 

 36-38. 



cBurrill and Blair, 1. c, p. 354. 



f« Clinton, G. C, Bui. 69, 111. Agr. Exp. Sta., p. 197. 



