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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, frequently 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, principal among which are the following: 
1. The ends of the very rapidly 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. This 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 (fig. 2,a). 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 ometimes 
in the internodes) there occur comparatively large swellings, caused by 
gum pockets formed in the wood (fig. 2, b). These pockets frequently 
become quite marked. 
Fic. 3.—Orange twigs showing effects of die-back; upper healthy, lower diseased. Natural size. 
3. Eruptions, caused by the bursting of the bark, very commonly 
occur on new and old twigs (fig. 3, lower twig, and PI. ITI, fig. 3). In 
such cases the tissue swells up, protrudes from the rupture, and becomes 
stained by the reddish-brown, resin-like exudation, which is so char- 
acteristic of the disease. These eruptions are very numerous, and in 
badly affected trees many limbs, from an inch in diameter down to the 
smallest, become thickly studded with them. This character almost 
invariably accompanies the disease and is present at all seasons of the 
year, so that it may probably be regarded as the principal symptom. 
Trees may be slightly atfected, however, and not show this symptom. 
4, In diseased trees rapidly grown young shoots often droop in a 
characteristic manner. After starting to push the twigs gradually 
bend downward and the ends turn up a little, giving the twigs a slightly 
S shaped curve. This, however, is not always a symptom of die-back, 
being occasionally seen in perfectly healthy trees. 
