2 BULLETIN 684, U. S. DEPAETMENT OF AGRICULTURE. 



purposes, since these diseases appear only in the early part of the 

 season when the apple is in a definite stage of development. With 

 bitter-rot, however, infections may occur from about June 15 until 

 well into September. If the weather is hot and moist and sources of 

 infection are present in sufficient numbers, the whole crop may be 

 destroyed within a week, almost before the orchardist is aware that 

 the disease has broken out. The writer has seen cases in ;which 

 the grower on visiting his orchard for the purpose of inspecting the 

 crop preparatory to picking has been surprised to find every apple 

 rendered worthless by bitter-rot, while only a few days before the 

 crop had appeared to be entirely free from disease. Naturally such 

 experiences as this cause southern growers to dread this rot more 

 than any other disease affecting the apple, with the possible exception 

 of pear blight. 



Estimates of the annual losses caused by apple bitter-rot are very- 

 difficult to make with any degree of accuracy because of the great 

 seasonal variation of the disease, due mainly to weather conditions 

 and because of the variation in the amount of damage done in differ- 

 ent sections from year to year. Local conditions also play a great 

 part in the variations of this disease. A local shower on a hot July 

 afternoon may supplj^ just the right conditions of extreme heat and 

 moisture to give the disease a beginning which finally may lead to 

 the total destruction of the apple crop, whereas a few miles away 

 conditions may be such that the disease is unable to gain headway 

 all season. 



Although the causal fungus is found in apple-growing sections 

 of States farther north and also in Europe and Australia, bitter-rot 

 is a serious disease only in the more southern apple-growing sections 

 of this country. Apparently the fungus is to be found in practically 

 every section of the world in which apples are grown, but is capable 

 of causing very serious losses only under the warm moist weather 

 conditions of the southern apple-growing sections of the United 

 States. According to Edgerton (7)^ and Schneider- Orelli (11), 

 the fungus as it occurs in the northern United States and in Europe 

 is physiologically different from the fungus associated with the 

 serious bitter-rot of the Southern States. 



Bitter-rot is typically a hot- weather disease. Accordingly, the hot 

 weather of the South coupled with sufficient moisture for germina- 

 tion of the spores is peculiarly favorable to its development. Ideal 

 weig,ther for bitter-rot infections is furnished by high temperature 

 and high humidity with the interspersion of frequent showers. 



The earliest reference to apple bitter-rot is usually credited to 

 Berkeley (2) in 1856, but Kicker (9) in 1916 discovered a reference 



^ The serial numbers in parentheses refer to " Literature cited," at the end of this 

 bulletin. 



