Citrus Nutrient Deficiency

This looks like a common nutrient deficiency on citrus trees. Possibly an overall deficiency of nutrients that may be caused by restricted root growth, insufficient water, or lack of nutrients for growth stages. Citrus need both macronutrients like nitrogen, phosphorous and potassium as well as micronutrients like zinc and iron, to name just a few of those. Deficiency can be caused by poor soil composition, incorrect soil pH, inappropriate water for root depth/root mass, or lack of proper fertilization. We’ve inlcuded some weblinks to help you determine the best course of action for your situation.
http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/citrus.html
http://edis.ifas.ufl.edu/ch142
http://www.ipm.ucdavis.edu/PMG/C107/m107bpleaftwigdis.html