Answer: It is difficult to diagnose the problem with your tangerine tree without actually seeing the damage and investigating further. Twig dieback can be caused by fungi, although cultural practices may also cause this problem. Fungal infection is often secondary, following freeze damage or damage resulting from mechanical or chemical injury. Other factors that can damage twigs are excessive fertilization, moisture stress and damage to the root system by cultural practices or heavy nematode damage. Affected young branches die back 1 inch or more from the tip, sometimes showing gum exudation. Damage by twig dieback usually is not severe.
The dieback might also be caused by an insect. Specifically, larvae of the lemon tree borer spend two years feeding and developing inside the stems of host trees. External evidence of their activities is seen in piles of 'sawdust' and frass at the entrances of holes in the wood. Feeding by the larger larvae causes die back of branches which must then be cut out.
Hope this information helps you determine whether the problem is caused by excessive fertilization, moisture stress, winter damage, or insects.
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