2010 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



Fig. 3. Bacteriosis on Large Nuts, Stigma or Blossom End Infection. Section of two 

 nuts, tlie one below affected with bacteriosis ; above, normal nut. 



It is not probable that insects play 

 much part in the dissemination of the 

 disease, although the organism has been 

 isolated from flies which were found 

 around walnut trees affected with blight. 

 A species of aphis is often abundant on 

 the leaves (rarely found on the nuts and 

 branches) that probably causes some leaf 

 infection, as well as a sooty deposit on 

 nuts and leaves. 



Natural Resistance 



Considerable variation exists between 

 individual varieties as to susceptibility 

 to blight. The walnut groves of the past, 

 and largely of the present, are seedlings. 

 Individual trees often show considerable 

 resistance to blight. This immunity in 

 a large measure is due to a later blooming 

 period. The difference in time of bloom- 

 ing is frequently one to three months be- 

 tween the earliest and the latest French 

 varieties. Such a wide range in time of 

 blooming gives considerable chance for 

 difference in climatic conditions. Some of 

 these late varieties are comparatively free 

 from blight, although no variety is 

 thought to be immune to the disease, and 

 even some of the most resistant and for 



this and other reasons most desirable 

 kinds will show, during certain seasons 

 and in certain localities, some blighted 

 nuts. The number, however, is so small 

 as to be of little commercial importance. 

 A variety should not be propagated alone 

 for blight resistance, unless the other 

 characteristics of a good nut are present. 

 It is more profitable to grow a productive 

 tree that gives some blighted nuts than a 

 scant producer that never blights. It has 

 become the practice among the best wal- 

 nut growers of California to graft over 

 their worst blighting and poorest yielding 

 trees to better varieties. Doing this a 

 little every year does not diminish the 

 yearly output to any marked extent, and 

 in a few years the crop will be increased. 

 Freedom from blight is not of necessity 

 resistance, but may be due to the fact that 

 the disease is not yet present or the con- 

 ditions are unfavorable for blight devel- 

 opment. Care should be exercised in con- 

 cluding too hastily that a given variety 

 is resistant before it has been tested in 

 sections and groves that show this dis- 

 ease. The most promising means of con- 

 trol will be secured by growing more re- 

 sistant and better varieties of walnut. 



