86 MISC. PUBLICATION 168, U. S. DEPT. OF AGRICULTURE 



quently in the early stages of the rot there are dark-brown 

 spots around the lenticels, about % inch in diameter, which in 

 their final form become reddish brown and have pale or whitish 

 centers. These spots continue to give the fruit a freckled appear- 

 ance even after it is completely rotted. 



The initial infection usually occurs at the stem or the calyx 

 end. The decay spreads from an infected fruit to surrounding 

 fruits in contact with it. Secondary infection may occur any- 

 where on an apple, depending on the point of contact with the 

 initially decayed fruit. Because the fungus can grow from dis- 

 eased fruits to healthy ones lying near or touching them it often 

 produces "nests," or "pockets," of decaying fruits in the stored 

 package. Hence, the disease is often called nest rot, or cluster 

 rot (pi. 18). Gray mold rot develops faster at cold-storage tem- 

 peratures than any other fungus rot of apples. Apples carrying 

 infection when placed in storage at 30° to 32° F. are often com- 

 pletely decayed by February or March. 



CONTROL MEASURES 



It is believed that the source of gray mold infection is in the 

 orchard. The fungus grows and sporulates abundantly on dead 

 and dying plant material found in orchard cover crops, especially 

 during cool, moist weather. Fruits hanging near the ground are 

 more likely to become infected than those farther from it. As 

 mentioned earlier, fruits infected at the time of storage nearly 

 always decay at the stem or the calyx end. The spores lodge in 

 these cavities and under favorable conditions may develop and 

 attack the stem or calyx sepals. From such superficial infection 

 the fungus spreads to the edible part of the fruit. Some measure 

 of control may be obtained by keeping the cover crop closely 

 clipped around the trees, to permit better air circulation and thus 

 to reduce dampness and certain other factors favorable to fungus 

 development. 



Picked fruit should not be left in the orchard. Additional 

 reduction in fruit decay may be had by using a disinfecting wash 

 at packing time. (See Pears, Gray Mold Rot, p. 59.) 



(See 11, 12, 29, 30, 59, 60, 61, 11U, 186.) 



Hail Injury 



Early-season hail injury generally occurs at the calyx end 

 or on one side of an apple, because of the position of the fruit 

 on the tree during this period. Later, when the fruit has become 

 larger and heavier, it generally turns downward; so hail marks 

 on well-developed fruits are more often on the stem end. 



Fruits injured early tend to outgrow the internal condition 

 produced, but they may become slightly misshapen as they develop. 

 When fruits are struck by hail late in the season, the cuticle 

 covering the affected spots may be cracked or torn but often 

 remains intact. Such spots range from % to */2 m ch in diameter 

 and are slightly sunken; the flesh beneath them is brown and 

 somewhat spongy and dry, because of loss of water from the 

 bruised area (pi. 3, D). The spots are usually dry enough when 

 the fruit is shipped not to be subject to rot infection, even if there 

 are cracks in the skin and flesh. 



