31 



where it first appeared has not yet been determined. Growers 

 have known of its occurrence for years, presumably ever since 

 orange culture became common in the State. 



The damage caused by die-back is much greater than is 

 usually estimated. Many growers have suffered for years from 

 slight attacks of the disease, the damage being caused mainly 

 by the excessive dropping of the fruit, and by the coarseness 

 and staining of that which remains on the trees. In some 

 severe cases due to improper fertilisation and cultivation, 

 groves have been badly injured and almost the entire crop of 

 fruit lost. Frequently much loss is incurred by planting trees 

 on improper soils and continuing to cultivate and fertilise them 

 for years after they contract the disease. Almost every grove 

 in the State has a few cases of this disease. Trees growing in 

 the vicinity of stables, chicken houses, privies, etc., are the 

 ones generally affected, and also those growing on the margins 

 of lakes, or on low wet, poorly drained soils. 



The diminished productiveness of trees badly affected with 

 die-back, together with the splitting and falling of much of the 

 fruit and the disfigurement and coarseness of that which does 

 develop, makes such trees almost worthless. The malady 

 causes great loss of fruit, renders more of poor quality, fre- 

 quently permanently stunts the tree and eventually kills it. 

 The annual loss resulting from die-back in Florida may be 

 conservatively estimated at about $100,000. 



Symptoms. — Die-back has probably more characteristic 

 symptoms than any known plant disease, principally among 

 which are the following : — 



1. The ends of the very rapid growing shoots turn yellowish 

 before maturing, and finally become stained reddish brown in 

 patches or throughout. This appearance is caused by a deposit 

 in the outer cells of a reddish brown resin like substance. 

 The yellowing and staining of the twigs, which is very 

 general on the new growth all over the tree, is followed by the 

 dying back of the affected twigs for a short distance usually 3 

 to 6 inches. The reddish stain may occur on the twigs back of 

 the point to which they die, and indeed may spread in irregular 

 patches more or less over the entire new growth. 



2. On the new growth (most frequently at the nodes, but 

 sometimes the inter-nodes) there occur comparatively large 

 swellings, caused by gum pockets formed in the wood. These 

 pockets frequently become quite marked. 



3. Eruptions caused by the bursting of the bark, very com- 

 monly occur on old and new twigs. In such cases the tissue 

 swells up, protrudes from the rupture, and becomes stained by 



