232 THE MONTHLY BULLETIN. 



badly attacked, there is a peculiar result. The bark of the twigs rots 

 away, leaving the tree full of dead white twigs which may persist and 

 not decay for several years. 



Later in the season the effects of the disease are masked by the new 

 growth. To find it at this time, one must examine those branches under 

 three-quarters of an inch in diameter for the presence of the cankers. 



Causal Organism. 



Prom the time of the discovery of the disease, all the indications have 

 pointed to a bacterial causal organism. In fact, the resemblance in its 

 effects to pear blight is very striking. (See Fig. 59.) Mr. H. A. Lee, 

 formerly of the University of California and now stationed at Washing- 

 ton, D. C, has worked on this disease, using material sent in from 

 various parts of the state, and has isolated the causal organism, a bac- 

 terium, which he calls Bacterium citra re facie >is. He finds that the bac- 

 teria exists chiefly in the parenchyma tissue, destroying the cell 

 structure, and that they do not ordinarily invade the vascular tissues. 

 He has further succeeded in isolating the bacteria from material which 

 has spent the summer in a dried condition, establishing the fact that 

 the disease may exist over the summer in the dead wood. 



Distribution. 



Citrus blast was reported at Oroville, Palermo, Wyandotte and 

 Orland in 1914. Since that time it has apparently spread rapidly both 

 north and south, having been reported as far south as Porterville. 



Inasmuch as this disease first manifested its economic importance in 

 1915, at which time it was confined to two local areas, its spread must 

 be considered very rapid and. as it is so new and little known to orchard- 

 ists, it is quite possible that it may have a much wider distribution 

 than is now suspected. As yet no report of this trouble has come from 

 the southern California citrus district. 



Reduces Fruit Wood. 



Citrus fruit is produced on wood of the current season's growth. This 

 puts out in early spring, bearing the fruit buds which open in April. 

 As has been stated above, under favorable moisture and temperature 

 conditions this tender new growth may be very seriously attacked by 

 citrus blast. Depending on the stage of growth in this new wood, the 

 character of the damage varies. Attacks early in the season may kill 

 all this fruiting brush back to the old wood, but if weather conditions 

 change it may be killed back only part way. 



In the event that the first named condition occurs, new fruiting brush 

 must be grown, and this draws on the reserve food and strength of the 

 tree. Blooming is delayed several weeks and the normal processes of 

 nutrition in the tree so weakened and disturbed that the proportion of 

 fruit "setting" may be reduced. 



If the new wood is only killed back part way. a resprouting of the 

 uninjured portion occurs which, while not delaying blooming so long, 

 may have the same general effect as the damage in the previous ease. In 

 addition, this resproutin<* may result in an abnormal clustering of the 

 flowers, which is not desirable. 



It very frequently happens in northern citrus districts that the trees 

 are in bioom when conditions occur which are favorable to the disease. 



