Managing Micronutrients in HLB-Affected Trees

By Davie Kadyampakeni

Nutrients are needed for optimal tree growth, fruit yields and juice quality. Any nutrient deficiencies could result in low yields and decreased revenue, so it is essential to make sure citrus trees receive adequate nutrient supplies at all times.

Micronutrients, though required in minute quantities, are especially important for citrus trees impacted by citrus greening. Examples of micronutrients include boron, zinc, iron, manganese, copper and others. Micronutrients are known to improve the accessibility and movement of macronutrients in the plant. Apply these micronutrients to the rootzone via fertigation or spreaders to ensure improved root flushes and overall tree health. Supplemental foliar sprays can ensure any deficiencies are corrected in real time.

For optimal availability of nutrients, follow these practices:

• Periodically do a soil test for pH and keep the soil pH between 5.8 and 6.5. Results have shown that this is the optimal range for nutrient availability in citrus-producing soils, especially for trees affected by citrus greening. If the soil pH falls below 5.8, it is highly recommended to apply lime. If the soil pH rises above 6.5, apply elemental sulfur or some acids to lower the pH to the desired 5.8–6.5 range.
• Perform a leaf tissue test at least once every quarter and make sure every nutrient is in the optimal or high range according to current University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) recommendations.
• Do a soil test at least once a year. But pay attention to the leaf tissue results because while some soil tests may show high nutrient content, the nutrient may not be readily available to the plant.
• When a leaf nutrient test shows excessive nutrient concentration, consider omitting that nutrient in the next four to six months to make sure it reverts to the optimal or high range. Excessive nutrient concentration may result in too much vegetative growth at the expense of fruit yield and juice quality.
• Split applications of micronutrients are encouraged. For example, if using fertigation, then apply a minimum of 12 splits per year. If using dry soluble fertilizer, four split applications are ideal. If using controlled or slow-release fertilizer, apply it two to three times per year.

Davie Kadyampakeni is an assistant professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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