Pomona College Journal of Economic Botany 81 



smaller top and indigestion or malnutrition begins which in turn produces die- 

 back. In such cases Mr. Hume recommends root-pruning. He says : "The amount 

 of pruning required will depend upon the severity of the attack, the size of the 

 tree and the character of the soil. Pruning may be done by cutting a circle around 

 the tree with a sharp spade, thrusting it well into the soil so as to sever a large 

 number of roots. The balance of the tree is restored by this method, and a complete 

 recovery frequently follows this practice. It should be borne in mind, however, 

 that in addition to this treatment, the cause of the disorder in the tree should be 

 sought for and the conditions favoring the development of the die-back removed 

 as far as possible." 



Spraying For Die-Back— So far as I have been able to discover no work of 

 this sort has ever been published as referring to such method of control in this 

 state. Again, we must go to Florida, where it is claimed that very good results 

 have been obtained by the use of Bordeaux Mixture. It must be remembered, 

 however, that an underlying hardpan cannot be remedied by the application of 

 sprays. In such cases, and in all cases, in fact, the cause of the malady must first 

 be sought and remedied as far as possible. It is then that good results may be 

 expected from the application of sprays. The Bordeaux Mixture is attributed by 

 Hume as accelerating the assimilative processes in the leaves and other green 

 parts of the tree due to the "chemo-toxic" effects of the solution, and not as a 

 fungicide in the ordinary sense. 



The mixture used for this spray is as follows: 



Copper Sulphate (Bluestone) 6 pounds 



Unslacked Lime 4 pounds 



Water 50 gallons 



Since a 4-4-50 Bordeaux Mixture has been found effective in spraying for the 

 wither-tip disease, it might be possible to get good results with this spray on die- 

 back at the same application. 



Relation of Die-back to Wither-tip — While these diseases arc widely separate 

 in characters and methods of attack, yet they are often associated together on 

 the same trees. The die-back, by weakening the tree, affords an excellent start- 

 ing place for the wither-tip. Thus a slight attack of die-back may be followed 

 by a severe attack of wither-tip without the presence of the die-back being mani- 

 fested. This very thing happened in a Valencia orchard near Santa Paula this 

 winter, and it was only after the wither-tip had abated that the die-back showed up. 



The stained fruit of the die-back presents the same reddish-brown color of the 

 so-called "red spot" of the wither-tip and where there arc no splits, may be con- 

 fused with it, unless careful observations are made. In the case of the die-back 

 the red spots are never depressed, while in the case of wither-tip they are de- 

 pressed and in more advanced stages present dark-colored fruiting bodies, while 

 in the advanced stages of the die-back the red spots appear as pads and are ac- 

 companied by splitting of the rind. 



