Question: How do I recognize iron deficiency in my plants? How do I correct it?Answer: Iron deficiency, or chlorosis, shows up first and most prominently on the newest growth (toward the ends of the branches and twigs). Look for yellowed leaves with dark green veins. It can progress into almost white leaf blades, then browned leaf tissues. It is a problem west of I-35 for the most part. Soils in the western two-thirds of Texas are alkaline and that turns the soil-borne iron into an insoluble form. You can either apply a foliar spray to bypass the roots or an iron additive to the soil, or you can add a sulfur soil acidifier to lower the pH, thereby releasing some of the insoluble iron. Arborists have iron products which can be injected directly into the trunks of chlorotic trees, although it will be only a temporary solution in most cases.
For the record, plants whose lower and internal leaves are turning yellow and falling have had some type of environmental stress, primarily drought.