Iron is a micronutrient citrus plants need for healthy growth. When citrus trees lack usable iron, they develop iron deficiency, also called iron chlorosis. This condition impacts the plant’s appearance and health. It manifests as a distinct yellowing of the leaves, indicating a disruption in chlorophyll production.
Recognizing Iron Deficiency in Citrus
Iron deficiency in citrus plants primarily affects younger leaves. The most notable sign is interveinal chlorosis, where the tissue between the leaf veins turns light green to pale yellow, while the veins themselves remain a darker green. This creates a mosaic or net-like pattern on the foliage.
As the deficiency progresses, pale yellow areas may become increasingly yellow, eventually turning ivory or almost white in acute cases. In very severe instances, even the smaller veins can lose their green color, leaving only the midrib with some green. This condition reduces leaf size and can lead to premature leaf shedding, twig dieback, and decreased tree vigor, affecting both fruit set and yield.
Underlying Causes of Iron Deficiency
Even when iron is present in the soil, several factors can prevent citrus plants from absorbing it effectively. High soil pH, particularly in alkaline or calcareous soils, is a primary cause. In such conditions, iron becomes chemically unavailable to the plant, even if it exists in the soil. This is often referred to as “lime-induced chlorosis”.
Poor drainage and prolonged wet soil conditions also contribute to iron deficiency by depleting root oxygen, hindering nutrient uptake. Low soil temperatures can further aggravate this problem. An excess of certain nutrients like phosphorus or heavy metals such as copper and manganese in the soil can induce iron deficiency in citrus. Compacted soils similarly impede root growth and nutrient absorption, making iron less accessible to the plant.
Effective Solutions and Prevention
Correcting existing iron deficiency and preventing its recurrence involves immediate and long-term strategies. Applying chelated iron is a highly effective solution for correcting iron chlorosis in citrus. Chelated iron is bound to an organic molecule, which prevents it from reacting with other soil components and keeps it available for plant uptake, even in alkaline soils. Its effectiveness varies based on soil pH.
Adjusting soil pH is a long-term preventive measure. For soils with a pH of 7.5 or higher, elemental sulfur or iron-sulfur can be incorporated to acidify the soil, making iron more available. This should be done carefully to avoid making the soil overly acidic. Foliar sprays containing chelated iron can offer quick but temporary relief by directly delivering iron to the leaves, though their effectiveness can be limited by poor translocation and frequent application, especially for large trees.
Long-term soil management practices are also important for prevention. Improving soil drainage helps prevent prolonged wet conditions that inhibit iron uptake. Avoiding over-fertilization with nutrients like phosphorus, which can antagonize iron absorption, is also beneficial. Selecting appropriate rootstocks that are more tolerant to low iron stress is another proactive measure for new plantings.