26 MISC. PUBLICATION 4 98, U. S. DEPT. OF AGRICULTURE 



scribed above it does not show the cracking so often seen on oranges. 

 So far as known it has no harmful eifect on the carrying quality of 

 grapefruit. 



CAUSAL FACTORS 



The cause of exanthema is not known. The disease is found most 

 commonly, however, on trees where there is poor drainage and where 

 the soil is underlain by hardpan, is subject to irregular moisture con- 

 ditions, or has been given excessive cultivation. It is also found on 

 trees oversupplied with organic nitrogen. It seems to be a nutritional 

 disorder, possibly due to copper deficiency, under certain growth 

 conditions. 



CONTROL MEASURES 



The most important thing to do in attempting to control exanthema 

 is to ascertain, if possible, the soil condition or cultural practice that 

 induced its development and to correct this by providing the trees 

 with the proper conditions for making normal growth. This may 

 mean any of the following procedures: (1) Blasting hardpan or cut- 

 ting ditches through it, (2) withholding nitrogenous fertilizers, or 

 (3) stopping cultivation during most of the year. If it is evident that 

 exanthema has not been brought on by overfeeding, small quantities 

 of stable manure may be helpful in controlling the disease. 



In Florida good results in controlling exanthema have been obtained 

 by spreading copper sulfate on the soil under affected trees at the rate 

 of one-fourth pound to 4 pounds to each tree, the quantity used de- 

 pending on the size of the tree ; and by spraying with bordeaux mix- 

 ture. Copper sprays applied for scab or melanose also control exan- 

 thema, although the evidence suggests that improvement results from 

 correcting a copper deficiency rather than from killing an organism 

 by the spray. 

 * (See 43, 51, 96.) 



FLORIDA RED SCALE 

 ( Ch njso mph a 1 u 8 a n id u m ( L. ) ) 



The Florida red scale infests citrus and mangoes (tree and fruit) 

 and many other plants in the Gulf States and other subtropical regions. 

 The female scale is dark reddish brown with a conspicuous light-brown 

 center, almost circular in outline, and about one-twelfth of an inch in 

 diameter when full-grown (see pi. 18, E.) Most of the injury that it 

 causes is through the extraction of sap from the leaves and fruit. It 

 has been observed that areas of the rind that are heavily infested with 

 Florida red scale frequently show rind break-down and drying out. 



Fruit infestation usually occurs during the summer or early fall. 

 If more than slight, it is likely to result in a roughening of the rind, 

 with shallow depressions where the scales were located. Infested 

 fruit loses its green color more slowly than scale-free fruit, although 

 the infestation may have been killed either by natural means or by 

 the use of sprays prior to harvesting. It is exceedingly difficult to 

 completely degreen with ethylene early ripening crops attacked by 

 Florida red scale. On the tree the fruit will eventually attain full 

 color, and the rind may become smooth after the scale has been killed, 

 but this takes a long time, 



Spraving with oil is recommended for the control of this scale. 



(See 81, 04, 100, 131, 132, U6.) 



