20 MANUAL OF FRUIT DISEASES 



The history of bitter-rot shows that it has always been spas- 

 modic and erratic in its occurrence in different seasons. But 

 the irregularity is not confined alone to different seasons, for it 

 makes its appearance in different years at different dates. In 

 different orchards it may occur at widely separated intervals 

 during the same season. The fruits on the sunny side of a tree 

 frequently are destroyed first. Sometimes the crop on the 

 south side of a tree is destroyed while on the north side it es- 

 capes the disease. Likewise the fruit on the inside, lower 

 branches, being well protected from the sun, often escapes, 

 whereas apples exposed to the sun are ruined. Trees in the 

 shaded mountain hollows of Virginia are said to show less rot 

 than trees in situations more exposed to the sun. 



All of these points indicate a decidedly close relationship 

 between the fungus and the weather, especially temperature. 

 The fact that the fungus is confined to the warmer states, that 

 it appears chiefly in July and August, and that fruits exposed 

 to the sun are destroyed first, point unmistakably to the fact 

 that the pathogene is a hot weather fungus. Furthermore 

 cold weather usually checks the disease or may stop it 

 altogether. A cold spring may retard the development of the 

 fungus at that season, but there usually results a later attack 

 on the fruit. In cool, dry summers bitter-rot is sparingly 

 present. Conditions most favorable for the development of 

 the disease are warm, moist weather. A short series of hot, 

 wet days in August may bring about a sudden and very 

 destructive attack. Nights with a heavy dew, alternating 

 with hot days, are usually followed by an extensive outbreak 

 of the disease, even destroying the whole crop in three days. 



Control of bitter-rot. 



Cankers, being a chief source of the inoculum, should be re- 

 moved. Remove the whole limb except where the affected 

 branch is a large and valuable one. Dead parts and cankers 

 other than bitter-rot lesions should be removed. All these 



