Symptoms
Iron chlorosis is the most common micronutrient problem of ornamentals, shrubs, vines, small fruits, and trees in Nort Eastern New Mexico.  Leaves in affected plants turn light green to yellow to white with distinct green veins in the leaf.  In severe cases, the leaves may be entirely white.
The margins of severely chlorotic leaves often scorch and die during hot periods. Some willows, oaks, and other plants may show dark spots between the veins.  Iron deficiency chlorosis may be  may vary during the season or year to year depending on environmental conditions. If iron chlorosis is persistent for several years, individual limbs or the entire plant may die.

Causes
Iron chlorosis is the result of the inability of the plant to extract sufficient iron from the soil.
New Mexico soils are typical of arid and semiarid soils around the world with lime or calcium carbonate in most of the soil profile. These soils are alkaline with pH ranging between 7.2 and 8.3.
Iron chlorosis is common in these soils and is exaggerated by excessive soil moisture, soil salinity, high concentrations of phosphorous, and relatively high concentrations of copper, manganese, and zinc in the soil, low or high soil temperatures, large additions of organic matter, or inefficient root function caused by nematodes or fungal pathogens. The most important factor is the presence of lime in the soil as a predisposing factor.
Plants vary in their ability to obtain and utilize iron. This is particularly evident when adjacent plants may show marked differences in chlorosis. Some plant species are capable of obtaining iron from alkaline soils whereas others cannot be grown successfully in native high Ph soils.

Control
Preventing and controlling iron chlorosis is difficult and often gives poor results. The following are recommended procedures for controlling iron chlorosis:
Soil moisture management: Water management is probably the most important consideration when growing plants in alkaline soils. In excessively wet or poorly drained soils, the chemistry of the soil changes and iron becomes unavailable. Irrigation applications should wet the plant root zone and should not be repeated until the soil moisture has been reduced by plant use and evaporation. Frequent irrigation in heavy clay soils or cold temperatures often results in a persistent deficiency of iron.

Correction
Numerous iron compounds are available for treating iron chlorosis; however, responses to soil and foliar applied materials varies considerably and no single product has proven to be consistently successful.
Soil Application: Many compound labels claim to correct iron chlorosis; however, most do not work in our highly buffered, alkaline soils.
Inorganic iron sulfate will give good results when applied to turf but their utility in other situations is generally unsuccessful. Iron sulfate will cause unsightly rust-colored spots on pavement when misapplied.
Chelated compounds must be placed into the root zone to be most effective. Incorporate lightly into the soil or irrigate in. Applications should be made in the spring to coincide with the first flush of growth. In most cases, it is necessary to treat every year.
Soil incorporation of inorganic compounds such as iron sulfate are not effective in most Utah soils.
Foliar Application: Iron compounds sprayed on leaves give the most rapid but temporary response. Usually green spots can be seen on the leaves a few days after spraying. Repeated applications are necessary as new foliage appears.
Chelated iron compounds or 0.1% ferrous sulfate can be applied as foliar sprays. Use a spreader-sticker to obtain better results. Avoid applications when fruit are present because staining may occur.

Tom Dominguez is an agent with the Quay County Extension, NMSUExtension Service. He can be reached by calling 461-0562 or emailing todomingu@nmsu.edu