76 



Pomona College Journal of Economic Botany 



Old — The old twigs present much the same symptoms as do the young. The 

 bark erupts and the characteristic reddish-brown stain pads are formed. The af- 

 fection takes place only in the bark, which is sufficient to kill back old branches 

 almost to the trunk of the tree. In this state I have been unable to find such a 

 case, but it has been reported as occuring in the San Gabriel valley before the 

 year 1902. In Ventura county we find only the young and tender growth killed 

 back. 



Leaves 



The leaves first turn yellow, as described above, and may or may not fall. Those 

 that do not fall soon begin to show an exudation of gum and the formation of regu- 

 lar or irregular reddish-brown pads over both surfaces, but usually beginning near 

 the mid-ribs and spreading outwardly. Swingle and Webber attribute much of the 

 staining of the leaves as due to the punctures made by scale insects and red spiders, 

 claiming that in many instances the infection takes place only where the tissues 

 were injured.* It is also claimed that the leaves are usually larger and longer 

 than on a normal tree. This has been observed here, but we attributed it to the 

 formation of the so-called water-sprouts caused by the die-back disease which al- 

 ways produce very large leaves. 



On a tree that is just beginning to show symptoms of having die-back the leaves 

 appear a deep green color, which is characteristic of an orchard well fed. Of 

 course such a color cannot be taken as an indication of this disease, since all healthy 

 groves show a deep green foliage. 



Fruit 



(Figures 29 B and 30) 



Discoloration — When the fruit is about the size of an average walnut it begins 

 to assume a lighter color and may even turn to a lemon yellow. At this stage it 

 begins to fall and may continue to do so until the last stages of the disease, when 

 there is very little left upon the tree. Soon the brown staining begins and may 

 cover the surface in patches of minute reddish-brown' speckles or in an unbroken 

 irregular blotch, which nearly covers the entire surface. 



Splitting — (Fig. 30). Accompanying the staining of the fruit is the splitting. 

 The splits or cracks first appear as small "chaps," which gradually lengthen and 

 widen until the core of the fruit may be exposed to view. This splitting may occur 

 even before the staining, but usually as stated above. The crack may begin on the 

 side of the fruit or at the blossom end. It is certainly disastrous to the market 

 value of the fruit, as the appearance is very repellent. The trees affected in this 

 county show great quantities of this insipid and split fruit, much of which is al- 

 ready on the ground. The fruit so cracked is called " ammoniated" fruit by Floyd. 



Gum-Pockets — Fruits which show splitting or which do not show splitting or 

 even staining, sometimes show the formation of small gum-pockets in the rind or 

 peel, just under the surface. This is found quite abundant on affected sour orange 

 trees. 



Again, there may be a formation of gum near the center of the fruit about the 

 seeds and core (Fig. 29 B). The dark area in the figure shows this. The gum so 



*Bull. No. 8, Dir. Veg. Phys. & Path., U. S. Dept. Agrcl., p. 17. 



