CITKUS DISEASES. 67 



non-parasitic influences, in particular to irregular water supply, or 

 other environmental factors. It has not been apparent, as far as 

 local conditions are concerned, that the nature of the soil, cultural 

 practices, or temperature changes have any relation to the disease. 



Control. 



There is but one possible course of action against scaly back. 

 Where a tree is very seriously attacked its removal is advised. A 

 young, healthy tree iii its place will soon more than make up for the 

 diminishing returns obtained from a scaly bark tree. As far as 

 observations show there is no danger of re-infection in replanting. 

 Where only small lesions occur, or where they are limited to one 

 or a few limbs tree surgery^ can be called into action. Diseased 

 branches can be removed, and areas on trunk and main limbs cut 

 out. as described under foot-rot. All precautions in the way of sterile 

 instruments, clean cuts, thoroughness in removal of affected tissues, 

 and final treatment of the wound are most advisable. The usual 

 reason for failure in this line of work is neglect to cut deep enough, 

 or far enough out around each lesion. Scraping off the dead scaly 

 bark is not sufficient ; the affected bark must be removed to the wood. 



Wliere this disease is present, regular inspections should be made 

 several times a year, followed by prompt treatment of all lesions 

 found. A system of tree numbering as recommended will aid m 

 keeping track of affected trees. 



GRAPEFRUIT GUMMOSIS. 



A type of disease very similar to psorosis appears to a limited 

 extent on the grapefruit, and is in fact by some workers considered 

 identical. This supposition is borne out by the observation that 

 where grapefruit and orange trees occur in the same block of trees 

 and are diseased, the oranges exhibit typical psorosis symtoms. the 

 grapefruit the somewhat different gummosis signs. Again this form 

 of disease cannot be clearly differentiated from foot-rot, the two 

 grading into each other, so that a line can be drawn only by calling 

 one a disease of the roots and crown, and the other a disease of the 

 trunk and limbs. 



Generall}^ speaking, this type of disease can be distinguished from 

 psorosis by the more copious gumming, the fact tliat it is limited to 



