DISEASES OF CULTIVATED PLANTS 651 



gether. At the common distance of forty feet the branches begin 

 to touch before the trees are ten years old, and by the time they reach 

 full bearing age, the ground is completely shaded and the tops of 

 the trees form a solid mass throughout. This condition is extremely 

 unfavorable to walnut production, and as the groves grow older is the 

 cause of more and more lessening of the crop. 



Another factor in walnut deterioration has been the common 

 idea that these trees require very little cultivation, irrigation, or fer- 

 tilization and the very irregular attention which they have received 

 in this respect. It is true that many walnut trees exist which receive 

 no cultivation whatever and produce very good crops. Such trees, 

 however, usually stand out by themselves with full exposure on all 

 sides, and moreover, while the ground about them is not cultivated, 

 it is at least subject to uniform conditions. The walnut tree seems 

 to particularly resent radical changes in soil treatment. It may do 

 well with no cultivation and will do better, other things being equal, 

 with good cultivation, but it is decidedly injured by irregular treat- 

 ment in this respect. 



Another feature of the situation is the fact that all our older 

 groves are seedling trees, growing thus on their own roots. The 

 English walnut root of the type most commonly grown in Southern 

 California is thrifty and vigorous when soil conditions are very 

 favorable, but has little ability to withstand hardship. Many of the 

 present walnut groves have been planted on soil which for one rea- 

 son or another is not well adapted to this root, and as a result the 

 trees gradually fail as they grow older. 



Again, the inherent nature of the trees in regard to quality and 

 quantity of production is responsible to a considerable extent for the 

 present unsatisfactory condition. Almost every walnut tree over ten 

 years of age in Santa Barbara, Ventura, Los Angeles, and Orange 

 counties is of the type known as the Santa Barbara soft shell seedling. 

 These have all descended from a few trees of the original planting of 

 Joseph Sexton and have in most cases been planted with no discrimi- 

 nation or selection of the nuts. As a result of this the type has de- 

 generated to a marked extent and a large proportion of the present 

 trees are decidedly inferior inheritently to their original parents. 



In addition to all this, the climatic conditions of the last two or 

 three years have 'been such as to have a decidedly unfavorable effect 

 upon w-alnuts, as described in other portions of this bulletin. The 

 case is, therefore, not altogether hopeless, since it is to be expected 

 that even under present conditions we may have better walnut sea- 

 sons and crops than those of the past few years. With better and 

 more regular cultural oare of the orchards which is now coming into 

 practice, there is still more hope for the future. Growers are begin- 

 ning to realize that some of the attention which they give their 

 orange and lemon groves might not be wasted upon walnuts. 



The faults outlined above may be counteracted to a considerable 

 extent by thinning out the closely planted trees, either by removing 

 a portion of the tops or taking out some of the trees bodily, and by 

 giving the groves cultivation, irrigation, and fertilization along ra- 



