UNITED STATES DEPARTMENT OF AGRICULTURE 



,„ BULLETIN No. 684 



V\ fsJ^^ Contribution from the Bureau of Plant Industry V 



^V?^"^^^ WM. A. TAYLOR, Chief S^IlS'^^^L, 



Washington, D. C. 



PROFESSIONAL PAPER 



August 19, 1918 



THE SOURCES OF APPLE BITTER-ROT 

 INFECTIONS. 



By John W. Robeets, Pathologist, Fruit-Disease Investigations. 



CONTENTS. 



Introduction 1 



Sources of infection 4 



Mummied fruits 4 



Bitter-rot cankers 7 



Cankers other than those of bitter-rot... 17 



Leaves 18 



Sources of infection — Contiaued. 



Other host plants 19 



Infected fruits of the current year 20 



Relation to control measures 21 



General summary 22 



Literature cited 24 



INTRODUCTION. 



In the more southern apple-growing sections of the United States 

 the disease having the common name bitter-rot or ripe-rot and 

 caused by the fungus Glomerella cingulata is one of the most de- 

 structive with which growers have to contend. In some seasons it 

 is undoubtedly the most destructive. The financial loss from apple 

 bitter-rot is increased by the fact that whereas such diseases as scab, 

 blotch, and blight destroy the crop in early spring or prevent its 

 setting at all, bitter-rot does not ordinarily begin until July and 

 usually does not complete its ravages until Septembei* or even later. 

 The grower, then, may during the early part of the season spend 

 his time and money spraying for the control of other diseases, such 

 as scab and. blotch, and of insect pests, only to see his fruit finally 

 succumb to bitter-rot in midseason, often despite his best efforts to 

 prevent it. As compared with the control of scab and blotchy which 

 are also important apple diseases in the South, the control of bitter- 

 rot is difficult of accomplishment. In the case of scab and blotch, 

 definite times can be set for the application of sprays for control 



51135°— 18— Bull. 684 1 



