The fungus can remain alive in these mummies 

 until the following year and then produce spores 

 to infect the new crop of fruit. 



The bitter rot fungus also may live over winter 

 in almost any cankered or dead part of the tree. 

 Once the fungus has become established in a twig 

 or branch, it may persist there for several years, 

 liberating spores each year to start anew the 

 cycle of fruit infection. Twigs and branches 

 that have been weakened or killed by low tem- 

 perature, or by diseases such as fire blight and 

 black rot, are particularly favored spots for 

 invasion. 



When the disease first appears each season, it 

 is not unusual to find evidence that rain has 

 washed spores down from infected twigs and 

 branches, and from mummies, to infect the fruit 

 immediately below. 



Control 



Apple injected with hitter rot 

 spores from a mummy above. 



Removal of mummies, cankered areas, dead 

 twigs, and branches which may harbor the bitter 

 rot fungus is a necessary control procedure. At 

 times outbreaks of bitter rot can be traced to a 

 few infected trees of a susceptible variety re- 

 maining in the orchard from a previous planting. 

 Such trees should be removed, for the value of 

 the fruit they produce is likely to be less than the 

 losses they cause by serving as a reservoir of 

 bitter rot spores that infect the fruit of adjacent 

 trees. 



After these early sanitary measures, a series 

 of fungicidal sprays must follow — applied at spe- 



cific times during the growing season. The first 

 spray should be applied before any infections 

 appear on the fruit. Since bitter rot rarely 

 appears before the middle of June, the first spray 

 is usually applied between June 10 and 15, a sec- 

 ond spray is applied about July 1, a third appli- 

 cation between July 15 and 20, and a fourth 

 application during the first week of August. In 

 orchards where the entire crop has been ruined 

 for several years, it may be necessary to start 

 spraying earlier than June 10-15 and to apply 

 the sprays every 2 weeks until the fungus is under 

 control. The sprays must be applied from all 

 sides of the tree so all the apples are covered. 



Bordeaux mixture 8-8-100, for many years the 

 standard spray material used for bitter rot con- 

 trol, has been largely supplanted by the organic 

 fungicides ferbam and captan. Sprays contain- 

 ing 2 pounds of either of these materials in 100 

 gallons of water are used. These sprays will 

 cause less injury to the leaves than the bordeaux 

 mixture. Dichlone, another organic compound, 

 used at the rate of % or 1 pound in 100 gallons 

 of water, is very effective but occasionally causes 

 a spotting of the leaves during periods of high 

 temperatures. 



All spraying leaves a residue on the fruit which 

 may interfere with its sale. No fruit should be 

 sprayed beyond the period recommended on the 

 fungicide container label, unless facilities are 

 available to wash or brush the fruit to remove the 

 spray residue before the fruit is offered for sale 

 or used at home. 



CAUTION 



Fungicides are poisonous; handle them with care. Read the 

 container label carefully. Follow all directions and heed all 

 precautions for storing, mixing, applying, and disposing of 

 fungicides. 



By John C. Dunegan, principal pathologist, retired, 

 Crops Research Division, Agricultural Research 

 Service. This publication supersedes Farmers' 

 Bulletin No. 938, Apple Bitter Rot and Its Control. 



Washington, D.C 



Issued September 1956 

 Slightly revised January 1964 



U.S. GOVERNMENT PRINTING OFTICE lfi — 72774-3 



For sale by the Superintendent of Documents. U.S. Government 

 Printing Office. Washington, D.C. 20401 - Price 5 cents 



