2012 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



adequate when trees reacli ten years or 



older. 



2. Lack of cultivation and fertiliza- 

 tion. 



3. Unfavorable soil for the walnut 

 root. This root requires a very deep, 

 porous soil. 



4. Deterioration of stock through im- 

 proper seed selection. 



5. Climatic conditions 



These faults suggest their own correc- 

 tion. 



R. E. Smith, 



California Experiment Station Bulletin 218. 

 Crown Gall— Black Knot. See Apple 

 Diseases. 



Die Back 

 The limbs die back from the ends, 

 sometimes for only a short distance and 

 sometimes down to the main forks of the 

 tree. All the limbs or only a part of 

 them may be affected Two general types 

 of die back may be distinguished, one on 

 the old trees, particularly "hard shells," 

 which die back slowly all over the top, 

 and another in young trees from two to 

 ten years old, which die back suddenly 

 during a single winter in part or all of 

 the limbs, or sometimes the whole tree 

 dies back clear to the ground. 



The former type of die back, affecting 

 old trees, occurs mostly on light soils, 

 where the trees are getting old and the 

 roots find insuificient moisture. Such dy- 

 ing back is also hastened by lack of cul- 

 tivation, irrigation and plant food, which 

 lack becomes more pronounced as the 

 trees grow older and the tops and roots 

 become more crowded. The only remedy 

 for this trouble is to thin out the trees 

 where they are too closely planted and 

 give the soil better care Most of these 

 old hard-shell orchards, even at best, have 

 now become so unprofitable and unde- 

 sirable as to make it seem better for the 

 owners to cut down the trees and use the 

 land for some other purpose. 



The second form of die back mentioned, 

 th^t occurring in young trees which have 

 formerly been thrifty, killing them down 

 to the forks or even to the ground, is a 

 very serious matter in some districts. 

 Tlie trouble shows usually to a greater 



extent in a certain portion of the orchard 

 or in certain orchards worse than in oth- 

 ers near by. 



This disease is practically the same in 

 its nature as that described as "Little 

 Leaf of the peach, and shows similar re- 

 lations. 



Trees affected in this way should be 

 pruned back to good live wood, if not too 

 far gone, and it is to be expected that a 

 new top will soon be produced. By proper 

 attention to irrigation late in the season, 

 especially in dry years, it is not to be ex- 

 pected that the trouble will occur again 

 save in soils most unsuitable for walnuts 

 on account of coarse subsoil near the sur- 



^^^^' R. E. Smith, 



California Experiment Station Bulletin 218. 



Leaf Diseases 



The walnut is attacked by a number of 

 leaf diseases, such as anthracnose or leaf 

 blight, leaf spot and mildew. 



These are likely to yield to spray treat- 

 ment if they should become serious. 



Little Leaf. See ^'Yellows,'* this sec- 

 tion. 



Mouse Injury. See Rodents. 



Oak Fungus. See Root Rot, this sec- 

 tion. 



Perforation 



The shell fails to develop properly, be- 

 ing only partially formed, with numerous 

 openings and thin places This appears to 

 be simply a lack of development due to 

 climatic conditions, and occurs in seasons 

 with a dry spring and a dry, hot summer. 

 Seems worse on trees attacked by aphis. 



Root Rot 

 Oak riingus— Toadstool Disease 



The English walnut root is quite sus- 

 ceptible to the so-called oak fungus or 

 toadstool disease, which occasions the loss 

 of many fruit trees of various kinds in 

 California. This disease consists in a 

 decay of the roots, in which the white 

 mycelium of the fungus may be found be- 

 tween the effected bark and wood. Occa- 

 sional clusters of toadstools appear at the 

 base of affected trees. The disease usually, 

 if not always, occurs in spots where oak 

 trees formerly stood, and when once start- 

 ed spreads from tree to tree in quite a 



