490 CALIFORNIA FRUITS : HOW TO GROW THEM 



Blights and Decays. There are several blights which are trace- 

 able to bacteria, parasitic growths which are not discernible as are the 

 fungi, and not usually amenable to spray treatment, because they exist 

 wholly within the tissues of the plant and are not reached by applica- 

 tions. The blights of the pear, the black heart of the apricot, the olive 

 tuberculosis, etc., are instances. Cutting back to healthy wood (with 

 tools dipped after each cut in corrosive sublimate, one part to one 

 thousand parts of water), and burning all removed parts, is the best 

 treatment which can at present be prescribed. 



The walnut blight, demonstrated by Newton B. Pierce, of Santa 

 Ana, to be caused by a bacterium, has so far resisted treatment, though 

 there seems to be promise of good results from spraying in February 

 or March, before growth begins, with the lime-sulphur wash. This 

 serves also for the reduction of walnut aphis, which is sometimes very 

 injurious to the tree and the crop.* The disease also affects the leaves 

 and young wood. The recourse seems walnut; generally worst at 

 the blossom end and usually first seen there early in the season ; later 

 the spots run together and encompass considerable areas of the surface. 

 As the disease progresses the nut is transformed into a hateful black 

 mass and is utterly destroyed. The disease also affects the leaves and 

 young wood, but does not attack the old wood and the roots as the 

 pear blight does. It is therefore more easily controlled. The recourse 

 seems to be toward resistant varieties, as stated in the chapter on the 

 walnut. 



DISEASES NOT TRACEABLE TO PARASITIC GROWTHS 



There are a number of prominent troubles which are not traceable 

 to parasitic invasion of any kind, and yet may be in some cases pro- 

 moted by bacterial growth invited by preceding conditions. 



Sour Sap. There is a fermentation of the sap, quite noticeable 

 by its odor, which may be found in all parts of the tree, from the root 

 to -the topmost twigs; sometimes in one part and not in another. Sour 

 sap in the root is generally due to standing water in the soil, and the 

 remedy is drainage. Trees thus affected make an effort to grow and then 

 the young growth shrivels. Severe cutting back of the top to reduce 

 evaporation until the roots can restore their feeding fibers is the only 

 treatment of the tree, and its success depends upon the extent of the 

 root injury. Sour sap may also be caused in the branches by the occur- 

 rence of frost after the sap flow has actually started. Cutting back the 

 diseased parts, as soon as discovered, to sound wood, is the proper 

 treatment. 



Die-Back. Dying back of twigs or branches may occur without 

 parasitic invasion through root-weakness or partial failure. It may 

 be due to standing water or to lack of soil moisture, either of which 

 will destroy the root-hairs and bring the tree into distress. The treat- 

 ment is cutting back to sound wood and correcting the soil conditions, 

 either by irrigation or drainage, as one or the other may be needed to 

 advance vigorous growth in the tree. 



*See Pacific Rural Press, March 7, 1914. 



