Citrus limb/twig dieback
The development of a certain amount of such wood is natural but excessive limb death, particularly in the tree interior and base of the canopy, may indicate a need for pruning.
Excessive twig dieback on the outside of canopies may result from a number of factors which cause defoliation including blight, pest or spray damage.
Micronutrient deficiency may be another factor and needs to be checked.
Zinc and Twig Dieback
Twig die back in citrus plants is a common symptom of zinc deficiency. It can be corrected using foliar sprays.
Limb die back can be a symptom of copper deficiency - particularly in young citrus. Gumming can also occur. See more on Citrus Gumming.
Growers should check using tissue analysis and apply the appropriate micronutrient fertilizer to the leaf to ensure supplies of the deficient nutrient are not limiting growth.