Iron Deficiency

Symptoms

Iron (Fe) deficiency appears as interveinal or uniform chlorosis of the newest leaves (Figs. 1 and 2). Older leaves remain green. In severely Fe-deficient palms, new leaflets may have necrotic tips, growth will be stunted, and the meristem may eventually die (Fig. 3). Early symptoms in Syagrus romanzoffiana, Rhapis spp., and some Licuala spp. appear as chlorotic new leaves covered with green spots 2 to 4 mm in diameter (Fig. 4).

May Be Confused With

Royal palm bug damage is very similar in royal palms, as both result in a general chlorosis of the spear and youngest leaf. Iron deficiency chlorosis will generally remain on the youngest leaf as it matures, while the yellowing caused by royal palm bug is transient and will eventually turn into leaflet necrosis and frizzling. Iron deficiency symptoms are commonly expressed in palms suffering from root suffocation, excesses of other micronutrients such as manganese, and root rot diseases, although in these cases, the iron deficiency is not the primary problem and will usually disappear if these other problems are corrected.

Cause

Iron deficiency is usually not caused by a lack of Fe in the soil, but rather by poor soil aeration or by planting palms too deeply. Both factors reduce root respiration and therefore active uptake of Fe. Root injury from root rot diseases will similarly be expressed above ground as Fe deficiency, since the root surface area available for interception and uptake of Fe will be greatly reduced in root rotted palms. High soil pH is the most common cause of Fe deficiency in broadleaf trees and shrubs, but in palms it is less likely to cause Fe deficiencies. Excessive uptake of other nutrient ions such as ammonium, phosphate, manganese, zinc, copper, and other heavy metals often results in Fe deficiency symptoms being expressed.

Occurrence

Fe deficiency is much more common in container production than in landscape or field nursery situations. Palms are typically slow-growing and may stay in a container for a year or longer. The organic components of container substrates tend to degrade into fine particles over time, reducing soil aeration in the process. Most palm species are susceptible to Fe deficiency under conditions of poor soil aeration, but Wodyetia bifurcata is particularly prone to Fe deficiency induced by high soil pH.

Additional Comments

Leaf Fe concentrations often show little or no relation to Fe chlorosis severity and are therefore not a reliable indicator of plant Fe status.

December 1, 2010