CALIFORNIA FRUITS: HOW TO GROW THEM 



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

 pear blight does. It is therefore less 1 serious, though it sometimes 

 considerably reduces the crop. The recourse seems to be toward 

 resistant varieties, as stated in the chapter on the walnut. 



DISEASES NOT TRACEABLE TO PARASITIC * GROWTHS 



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 an- 

 other. 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 the 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 occurrence of frost 

 after the sap flow has actually started. Cutting back the diseased 

 parts, as soon as discovered, to sound wood, is the proper treat- 

 ment. Serious injury to nursery trees which is sometimes called 

 "sour sap" is described on page 99. 



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 

 treatment is cutting back to sound wood and correcting the soil 

 conditions, either by irrigation or drainage, as one or the other may 

 be needed. 



Gummosis. Gumming is not always to be considered in itself 

 a disease, but rather an indication of conditions unfavorable to the 

 thrifty growth of the tree. It has been usually found by investi- 

 gation that trees in perfect condition of health, with the moisture 

 just enough and not excessive, are not troubled with gumming; 

 but there are cases in which this statement does not wholly apply. 

 Prof. H. S. Fawcett has demonstrated that in some cases it is com- 

 municable because of a fungus cause. Full accounts of this may 

 be had in University publications. 



When there is an outbreak of gum where it can be treated it is 

 desirable to cleanly remove all the unhealthy bark cutting clean 

 to sound bark and covering the wound with Bordeaux paste pre- 

 pared as follows : 



One pound of bluestone dissolved in 1 gallon of water in a wooden 

 or earthen vessel by hanging it in the top in a sack. Two pounds of 

 unslaked lime, slaked in about one-half gallon of water. Stir together 

 when cool, making a light blue mixture about the consistency of white- 

 wash. Apply with a brush. This may also be applied to healthy bark- 

 as a preventive against new infections. 



Root Knots. These are excrescences upon the roots or at the 

 root crown of various trees and of grape-vines. Some of the knots 

 have been studied and the cause demonstrated to be a fungus and 



