MARKET DISEASES OF FRUITS AND VEGETABLES 23 



because it shows sharkskin. Sharkskin is rare on oranges, but the 

 degree and period of infestation that produce it on grapefruit cause 

 the so-called black russet condition on oranges. 



(3) Injury caused by the common summer infestation. In this 

 type the russet ing usually occurs in solid though poorly defined areas 

 or patches that may involve most of the surface of the fruit. It is 

 also found in streaks about one-eighth to one-fourth inch wide, oc- 

 curring either alone or as extensions toward the blossom end from a 

 larger russet area on the top or side of the fruit. These streaks, 

 known as citrus rust mite tearstaining, were at one time thought to 

 be caused by the anthracnose fungus [Colktotrichum), but so far as 

 Florida is concerned are now known to be merely one form of citrus 

 rust mite injury (for other forms, see Grapefruit. Tearstaining, p. 10, 

 and Grapefruit. Melanose, p. 5). A similar-appearing injury of 

 lemons in California is known as tearstaining, but it is caused by the 

 anthracnose fungus (p. 3). 



(4) Injury by late fall or winter infestation. This is usually so 

 slight that it produces merely the so-called golden or bronze effect 

 that prevents the fruit from being classed as bright. 



Russeted fruit is less attractive in appearance than bright fruit 

 and brings a lower price. The injury to the skin does not seem to 

 render the fruit more liable to decay, but it does cause it to lose water 

 and shrivel rather rapidly under ordinary merchandising conditions. 



The citrus rust mite is light yellow, wedge-shaped, and, when full- 

 grown, about one two-hundredths of an inch long. It is not likely 

 to be found on fruit that has gone through the washing and polish- 

 ing processes in the packing house, but the evidence of its prior 

 presence, of course, remains. 



CONTROL MEASURES 



The best results in controlling the citrus rust mite have been 

 obtained by applying sulfur or some of its compounds either as a dust 

 or in the form of a spray, the applications being made at any time 

 when the mites are found to be unduly numerous. 



(See H, 100, 131, 132, 135.) 



COLORING-ROOM INJURY 



Citrus fruit subjected to ethylene treatment sometimes suffers an 

 injury that is characterized by a brown spotting of the rind (pi. 

 12. D). This spotting, often erroneously called "gas burn," is not 

 caused by ethylene but by too low humidity in the coloring room : it 

 is found on fruit subjected to dry air in which there is no trace of 

 coloring gas, as well as on gassed fruit. The brown spotting develops 

 on any part of the fruit during the gassing period and can be de- 

 tected readily when the fruit is graded in the packing house. In 

 general appearance it closely resembles brown stain (p. 21) but is 

 perhaps a little darker in color. This is especially true on grape- 

 fruit. The discolored areas rarely enlarge after the fruit is packed 

 and seldom afford an avenue for the entrance of decay organisms. 



This blemish is likely to be encountered early in the season when 

 the fruit is tender and relatively immature. It has usually been 

 found where attempts were being made to "force" coloring by the 



