Iron deficiency in landscape plants that require an acid soil will cause young leaves to turn yellow while the main veins remain green. In advanced stages, brown spots occur between the leaf veins.
Plants commonly affected by iron deficiency are pin oak, azalea, blueberry, rhododendron and holly.
To treat plants, spray them with iron chelates. These are available from most nurseries and garden centers and provide a suitable solution for small plants. Spraying large trees is not practical. Use trunk implants of soluble iron sources on trees. The plastic capsules are inserted into holes drilled in the trunks.