Apple Bitter Rot 



What Is It? 



Apple bitter rot is a fungus disease that in years 

 past destroyed many crops of apples in the more 

 southern orchards east of the Rocky Mountains. 

 Fortunately, improvements in spraying methods and 

 materials in recent years have, for the most part, 

 eliminated this problem in commercial orchards, but 

 the disease is still present in home orchards and 

 small plantings that are not regularly treated with 

 effective fungicides. 



As the name suggests, bitter rot is principally a 

 disease of the fruit. Growth of the fungus causing 

 the rot is favored by periods of rainy weather with 

 temperatures between 70° and 80° F. It is a mid- 

 summer disease mainly spread by rain and insects. 

 Although the disease is more prevalent in the South, 

 it is found occasionally in northern orchards. 



Varieties Affected 



Apple varieties show considerable difference in 

 susceptibility to the bitter rot fungus. Golden De- 

 licious, Jonathan, Yellow Newton, Northwestern 

 Greening, and Grimes Golden are generally more 

 susceptible than Rome Beauty, Staynian Winesap, 

 Delicious, York Imperial, and Winesap. This dif- 

 ference in susceptibility, however, is only relative, 

 for the infection of the fruit of any variety depends 

 to a large degree on the right climatic conditions and 

 nearness to sources of infection. 



The disease has also been observed on cherries, 

 pears, quinces, and peaches. 



Description 



The fungus causing apple bitter rot is able to pene- 

 trate the uninjured skin of the fruit, and the first 

 telltale sign of the disease is the appearance of small, 

 light-brown, circular spots under the skin. When 

 the spots are about half an inch in diameter, the 



skin becomes depressed and small sticky beads of 

 spores, arranged in a series of concentric circles, 

 break through the skin. At first the spore masses 

 are pink, but they later turn dark brown or black. 

 Circles of spore masses are an easily observed and 

 distinguishing symptom of the disease. Black rot, 

 a fungus disease sometimes confused with apple 

 bitter rot, does not produce these rings of spores. 



When the bitter rot spots are small, the rotted 

 flesh is watery, another means of distinguishing the 

 disease from black rot. Also characteristic of bitter 

 rot at the early stage is the cone shape of the decayed 

 areas, with the tips of the cones pointed toward the 

 seed cavity. As the fungus continues to grow, the 

 diseased areas lose their cone shape and the decay 

 eventually involves the entire apple. 



The number of spots on an apple may range from 

 1 to as many as 500 or 1,000. When the spots are 

 very numerous the individual spots remain small 

 and blisterlike, giving the apple a peculiar peppered 

 appearance. 



How It Overwinters 



Although most of the bitter-rot- infected apples 

 drop to the ground, the few that remain on the trees 

 eventually shrivel into hard masses called mummies. 



Bitter-rot-infected apples. Spore 

 • iiigs show well on apple ill left; 

 some spots on apple at right tire 

 early ones without spore rings. 



