y) BULLETIN 684, U. S. DEPARTMENT 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 svhich 
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 
dificult 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 supply 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 
weather 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 Ricker (9) in 1916 discovered a reference 
‘The serial numbers in parentheses refer to “ Literature cited,” at the end of this 
bulletin. 
