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Pomona College Journal of Economic Botany 



having the least idea of the cause of the trouble and the result being that little 

 good was accomplished. 



In California there have been no recorded facts with relation to the loss because 

 of this malady. As has been stated, it was claimed that whole groves were de- 

 stroyed before 1902 in the San Gabriel valley, and from time to time since then 

 reports have come in that the disease has done considerable damage. In the re- 

 ports of the State Pathologist for 1906 and from 1906-1909, the disease is men- 

 tioned as being more or less common, but no serious loss is recorded. In Ventura 

 county, where the writer has made his observations, the greatest amount of damage 

 may be accorded to a single orchard, where some twelve or fourteen trees are doing 

 absolutely nothing for the owner. Many other trees also show signs of the dis- 

 ease, but not to any great extent. No doubt the greatest amount of damage in 

 this state is in the production of stunted trees or "drones," which are doing ab- 

 solutely nothing and which are a source of anxiety to the owner who does not 

 know their ailments. Nothing could persuade the owner in Santa Paula that his 

 trees were affected with die-back, and he could not be induced, by any means, to 

 attempt any remedies. It is to be hoped that enough information can be given 

 the growers in this article to enable them to diagnose the cases and to attempt a 

 cure. 



Control Methods 



For Excess of Ammonia — Since an over-production of ammonia seems to cause 

 die-back it is necessary to employ some means of preventing the tree getting too 

 much in its food. This may be accomplished by cutting down the water supply and 

 by cultivating only enough to keep the tree in shape through dry spells. 



In plowing, all green manure crops or grass should be first removed from the 

 grove to prevent the addition of more nitrogen. If any fertilizing is necessary, 

 use sulphate of ammonia or nitrate of soda to obtain nitrogen. What has been 

 said applies to an orchard which has had an excessive application of organic nitro- 

 gen fertilizers. When the condition has been remedied small amounts of organic 

 fertilizers may be again applied, but with such fertilizers as stable manure, blood 

 and bone, dried blood, guano, cottonseed meal, and green manure crops, add also 

 potash and phosphoric acid. 



For Improper Soil Conditions — Drain low and poorly-drained soils so as to pre- 

 vent the over-accumulation of seepage water. 



Blast out the hardpan under the trees if it is possible. This method has been 

 very successful on soil of this type in Florida. Subsoilers may be used. 



Irrigate regularly so as to prevent over-irrigation at some periods and a scanty 

 supply at others. 



Cultivate so as to aerate the soil in case of heavy soils, and try to keep the 

 orchard in good condition. If this will not cure die-back it may be a good invest- 

 ment as a preventative. 



Fertilize so as to avoid an excess of ammonia as described above. 



Pruning in Relation to Die-back — According to H. H. Hume, die-back in Florida 

 often follows the freezing back of the tops, while the roots remain uninjured. The 

 result is that the amount of food supplied by the roots cannot be utilized by the 



