84 



THIRTY-FOURTH FRUIT-GROWERS ' CONVENTION. 



separated from the wood and killed by the exudation of guin, in 

 order to give an opportunity for new bark to form, and the wound 

 to heal over. This treatment is in no sense a remedy for the disease, 

 but simply a method of wound treatment, as might he applied in the 

 case of any injury. All bark which is badly affected should be stripped 

 cleanly from the tree, trimming neatly about the edges of the sound 

 bark, and the exposed wood should then be covered with some material 

 for Avhich a wax, composed of four parts resin, one part beeswax, and 

 one part raw linseed oil, boiled together and applied as a liquid with 

 a brush, is as good as anything. It is also advised to slit the bark of 

 affected trees up and down the trunk in several places. Orange trees 

 are sometimes affected in very wet ground. 



The scaly bark of the orange is of a nature much less easily explained. 

 The manner of its occurrence, affecting the trees here and there about 

 the orchard, makes it difficult to understand how it can result from con- 

 ditions which seem practically alike all over the orchard. The disease 

 is limited to the sweet orange, not affecting the lemon, grape fruit, or 

 other species, and is much more common on seedlings and navels than 

 on the Valencia. It manifests itself as a scabby, gumm}^ breaking out 

 at any point on the trunk or branches, and usually keeps spreading 

 about the trunk or along the branch from year to year. We can only 

 say, in regard to the nature of this disease, that the condition of the 

 affected tissues when studied with the miscroscope is similar to that in 

 the lemon gum disease. There is the same breaking out of gum through 

 the bark, wdth the difference that in this case it is less abundant and 

 active, and takes the form of a mild irritation, which keeps the affected 

 area continually spreading at a limited rate. In our opinion, the disease 

 is connected with an irregularity in the flow of sap up into the tree, 

 starting primarily in an irregular water supply to the roots, the trouble 

 resulting from interference with the flow of sap on account of the 

 structure of the wood, as has been previously mentioned. We feel 

 quite w^ell satisfied that the disease starts as a result of an abnormal 

 relation between the flow of sap and the structure of the wood, which 

 should conduct it, however obscure may be the cause which first brings 

 this about. We have seen cases of successful treatment of scaly bark 

 areas on orange trees, when not too large, by cutting out all the affected 

 part and covering the wound with the wax described above. In doing 

 this, it is necessary to cut away all bark which shows discoloration 

 between it and the wood, beyond the portion where the surface shows 

 the scaly condition. This is found particularly just above the visibly 

 affected portions. The practice of covering portions of trees affected 

 with scaly bark with a thick paste composed of lime and sulphur is 

 sometimes resorted to. We have not been able to observe any very 

 decided or permanent benefit from this treatment. 



Florida die-back, or exanthema, is another disease which may be 

 included in this class, and occurs to some extent in Southern California. 

 This is a disease of verj^ pronounced symptoms, both on the fruit and 

 twigs. It affects particularly the orange. The affected oranges show 

 dark brown discolored patches on the side, and from these places the 

 fruit often splits. The oranges have a characteristic pale yellowish- 

 green color, and are quite sweet when not more than half grown. The 

 branches die back from the tips, send out clusters of small shoots from 



