Iron is an immobile nutrient and is not moved from old growth to new growth to compensate for diminished supply. Therefore, iron deficiency symptoms appear on new growth, pointed out Jay Deputy, education specialist, Hawaii Cooperative Extension Service.
The most common and prominent symptom is interveinal chlorosis (yellowing) on young leaves, with the larger veins remaining green, Deputy said. Leaves may scorch as the severity of iron deficiency increases, and, if very severe, iron deficiency leads to reduced growth and shoot dieback.
“Iron deficiencies are sometimes difficult to diagnose and the symptoms are often confused with a manganese (Mn) deficiency,” he said. “Both result in interveinal chlorosis and appear under the same environmental conditions. In some cases, a Mn deficiency will include interveinal yellowing, but in this case the smallest veins remain green.”
The second difficulty in establishing an iron deficiency is that a tissue analysis by a laboratory will more than likely report the results in total iron and not available iron, Deputy said. “It is well documented that total iron values do not often correlate with an actual iron deficiency,” he explained. “So therefore, be careful in your diagnosis of the problem. A quick and dirty approach to help in the diagnosis of a suspected iron deficiency is to spray a few leaves with a ferrous sulfate or iron chelate solution. However, lack of a response does not in itself mean you do not have an iron problem. Iron deficiency most frequently results from high soil pH. It may also be induced by cold wet soils, compacted soils, and excessive Zn, PO4, or Mn.”
Several corrective approaches for iron deficiency have been used and have been successful for trees and some palms. These include injection treatments, Deputy said. “There has been considerable discussion about the potential negative impact of the wounds caused by trunk injection methods, so minimizing the hole diameter and number of holes is an important consideration,” he advised.
Deputy recommended a few cultural practices to minimize the problem, including avoiding over-irrigation and nutrient imbalances such as excess P or micronutrients (especially Mn and Zn). “For dicots, avoid fertilizers with large amounts of nitrate,” he added. “This is less effective for palms, grasses, etc. Avoid damaging roots and circumstances that tend to compact soils (e.g. construction traffic) Potassium (K+) salts and ammonium (NH4) forms of nitrogen generally improve an iron deficiency situation.”
The author is managing editor for Lawn & Landscape magazine and can be reached at nwisniewski@lawnandlandscape.com.