32 MISC. PUBLICATION 4 9 8, IT. S. DEPT. OF AGRICULTURE 



SPRAY INJURY 



If oil emulsions, either alone or in combination with bordeaux mix- 

 ture, are sprayed too heavily on citrus fruits or if the emulsion has not 

 been well made, they are likely to injure and spot the skin. Bordeaux- 

 oil injury is usually a splotchy, superficial russet, rarely penetrating 

 below the epidermis and rarely causing pitting (pi. 11, G and D) . Oil- 

 spray burn is more deep-seated, usually occurring as a depression like 

 a large pit where the last drop dried or where the rind was exposed to 

 the full rays of the sun. 



Lime-sulfur sunburn on Florida fruit occurs for the most part in 

 late summer after the rains have slackened and following applications 

 for citrus rust mite control. Grapefruit and Hamlin and other early 

 oranges are very susceptible (pi. 6, D). The blemish is found mostly 

 on the exposed surface of fruit on the southwest part of the tree. The 

 affected parts are slightly sunken with an abrupt margin having an 

 irregular outline. The epidermal cells are killed, first turning gray, 

 and later may crack and become invaded by fungi that produce dark 

 pimples on the gray surface tissue. The spots vary in size from three- 

 eighths to one inch in diameter. Decay ordinarily does not set in 

 at these points unless the fruit is held a long time. In such cases 

 Phomopsis, Diplodia, or Collet otrichwm may be the invader. (See 

 also Grapefruit, Sunburn, p. 9.) 



An injury somewhat similar to the type just described and also 

 caused by lime-sulfur burning occurs on citrus fruit from other regions. 

 In addition, another kind of lime-sulfur injury has been observed in 

 California (-fi), characterized by hard firm brown spots with gum 

 pockets underneath in the white portion of the rind. This spotting 

 is reported to occur most often on lemons in the coastal sections, and 

 usuallv on fruits facing the interior of the tree. 



(See 43.) 



STEM-END ROT 



(See Grapefruit, Stem-end Rot, p. 7. and pis. 5, A, and 6, A.) 



STYLAR-END ROT 



(Altcj'tiaria sp. and Fitsarium sp.) 



Stylar-end rot, commonly known as blossom-end rot, occurs on 

 oranges, and to a less extent on grapefruit, in Florida and the West 

 Indies. The disease is apparently due to physiological factors, prob- 

 ably unfavorable weather and soil conditions, which bring about a 

 weakened condition of both tree and fruit, slight cracking of the rind 

 at the stylar end, and eventually infection at the cracks by various 

 fungi. The first prominent symptom of the rot in affected fruits may 

 be any one or various combinations of the following: (1) A reddish- 

 orange color over most of the surface, developing several weeks ahead 

 of the normal yellowish orange color of the main crop; (2) a slightly 

 softened condition over an area half an inch or more in diameter, at 

 the stylar end, sometimes accompanied by browning at the center of 

 this area, and (3) a slight yellowing at the blossom end, with or with- 

 out browning at the center. 



When fruits showing these symptoms, especially the high color, are 

 cut lengthwise, they are usually found to be diseased on the inside, the 



