GENERAL DESCRIPTION. 15 



GENERAL DESCRIPTION OF THE BITTER ROT. 



TIME OF APPEARANCE. 



The bitter rot appears in an apple orchard at different times during 

 the months of July and August, the time of its first appearance vann- 

 ing with the climatic conditions during any particular season. The 

 first spots (PL IV, fig. 2) usually develop on the apple fruits when 

 they are nearly full grown. From that time on until the fruit is 

 entirely ripened the disease is likely to occur with increasing severity. 

 In the Southern States bitter rot may destroy some fruit in the early 

 part of July. In a number of cases apples only three-fourths of an 

 inch in diameter were found affected with the disease. One of the 

 writers collected apples affected with bitter rot in Vermont on Octo- 

 ber 20. The spots were small but well developed, and were present 

 on a large number of individual fruits on one tree. 



The factors which determine the time of appearance are probably 

 (1) the age of the fruits; (2) the temperature and humidity of the air; 

 (3) the presence of spore-distributing centers. The age of the fruit 

 is a factor of considerable importance. As a rule, the green fruit is 

 comparatively immune, which may be due in part to the large amount 

 of malic acid present in the unripened fruit. It is possible to produce 

 the disease on green fruits by artificial inoculation by allowing such 

 fruits to lie on a shelf for several days after being picked. Different 

 varieties of apples show a different susceptibility with respect to the 

 time of attack. No hard and fast rule can, however, be laid down in 

 respect to this matter, as the climatic conditions may hasten or retard 

 attack. 



Warm, sultry weather, particularly after a rain, forms the ideal con- 

 dition for the development of the bitter rot. In cool, dry summers the 

 bitter rot is usually present but sparingly. A short series of hot, wet 

 days in August may bring about a sudden and very destructive attack. 

 Nights with a heavy fall of dew alternating with hot days are usually 

 followed by an extensive development of the disease. Numerous 

 instances might be mentioned where the disease appeared in an orchard 

 during the latter part of August, after a few hot days, destroying the 

 whole crop in three days. A notable case of this kind occurred during 

 the summer of 1900. Cold weather usually checks the disease and 

 may stop it altogether. 



The time of appearance of this disease is probably influenced also 

 by the condition of ripeness of the spores in the cankers (as described 

 later) and in the mummies. A cold spring may retard their develop- 

 ment and consequently bring about a late attack on the fruit, or vice 

 versa. 



