MARKET DISEASES OF FRUITS AND VEGETABLES 33 



diseased condition manifesting itself as a gray, pink, or black discolor- 

 ation and a partial decomposition of the pithy core. On the other 

 hand, fruits showing merely splitting and a brown spot or even a 

 slight softening at the stylar end are often found perfectly sound in- 

 side when cut (pi. 13, E). The colors mentioned are apparently due 

 to the action of specific fungi, since Alternaria is always associated 

 with the gray or black color and Fusarium with the pink. Nothing 

 is known of when or how these fungi gain entrance into the fruit, but 

 it seems probable that they enter early in the life of the fruit, just as 

 in the case of black rot of California navel oranges. 



In advanced stages the rind at the stylar end becomes decayed in areas 

 of varying size up to V/ 2 or 2 inches in diameter, and like the affected 

 tissues on the inside shows a gray, pink, or black color. The symptoms 

 on grapefruit are practically the same as those on oranges except that 

 the extreme final stages of decay occur only rarely if at all. 



There are indications from holding and shipping tests that the rot 

 continues development in transit, though rather slowly . ^ Nothing is 

 known of methods of control. Observations in Florida indicate that 

 most of the affected fruit either falls or is picked off by January 1; 

 hence the rot is not likely to be of importance either in the packing or 

 on the market after that date. 



(See 33, 43.) 



THORN INJURY 



Injuries due to thorn punctures are often found on all kinds of citrus 

 fruit from all producing regions. When deep and well marked, such 

 injuries can hardly be mistaken for anything else. When shallow they 

 sometimes resemble bruises (pi. IT. A). 



Infection with decay-producing organisms may follow but is not 

 common. 



THRIPS INJURY 



(The citrus thrips, Scirtothrips citri (Moulton), in California, and the Florida 

 flower thrips, Frankliniella bispinosa (Morgan), in Florida.) 



The damage done by thrips to citrus trees and fruit is caused by the 

 feeding of both adults and larvae upon the surface of the parts at- 

 tacked. Feeding may be done on both young and nearly mature fruit 

 and on new and tender foliage. 



In California and Arizona thrips injury is of most importance on 

 oranges and, in its most characteristic form, occurs as a roughened 

 gray band or ring at the stem end (pi. 15, E). Occasionally more or 

 less irregular and indefinite roughened areas occur on other parts of 

 the fruit. Navel oranges are more frequently affected than Valencias. 

 Grapefruit, lemons, and tangerines are also attacked. 



True thrips injury is rare on Florida citrus fruit. The blemish 

 commonly called "thrips injury" on Florida fruit is now believed to 

 be merely the result of rubbing against leaves and twigs during late 

 winter or early spring while the fruit is young and small (pi. 18, A). 

 It has been found, for example, that when an orange tree was screened 

 against wind the so-called thrips injury did not develop; and, con- 

 versely, that on trees not so protected it did develop. Thrips were 

 present in large numbers on both the screened and the unscreened trees. 



466977°— 42 3 



