Micronutrient Management for Improved Citrus Productivity

By Davie Kadyampakeni, Alisheikh Atta and Muhammad Shahid

Micronutrients are those nutrients not required in large quantities but are important for improved tree performance. In the era of huanglongbing (HLB), micronutrients such as manganese (Mn), zinc (Zn), boron (B), iron (Fe) and copper (Cu) have become very critical for optimal tree management.

For example, B is known to help the mobilization of nitrogen in the tree while Mn and Zn help improve tree immunity and metabolism. Iron is important for the tree to make food. Copper is known to help with mitigating against diseases. Thus, it is important to keep the levels of micronutrients optimal throughout the year so the trees can have the best response and production.

USE TWO TYPES OF APPLICATION

While micronutrient fertilization before HLB was mostly done by foliar application, trees impacted by HLB have limited foliage and root mass. Thus, it is encouraged to apply micronutrients both to the foliage and soil.

Application of micronutrients is usually done up to four (or greater) times a year, such as in spring (two times), summer (once) and fall (once). As a rule of thumb, the more the splits, the better the efficacy of uptake.

It is recommended to apply at least one or two times to the rootzone via soil, and the other two applications to the foliage. By applying to the roots, one ensures micronutrients are ‘spoon-fed’ to the tree, which can improve root health and recovery. Foliar micronutrient sprays are considered the ‘urgent care’ of citrus production, where deficiencies are corrected.

CONSIDER THE SOURCE

Sources of micronutrients are also critical. Sources that are from nitrates and sulfates usually have greater micronutrient availability and uptake efficiency. Those micronutrients that are chelated, especially for nutrients such as Fe, become readily available in the soil.

Other nutrients, such as Cu, can easily be applied along with herbicides or pesticides and can be omitted in other foliar micronutrient sprays. Thus, it is important to critically look at the nutrient sources to ensure efficiency and efficacy of uptake and use.

ALWAYS ANALYZE

Finally, all applications should be based on leaf and soil analysis. If leaf analysis shows a deficiency or low level, consider applying that micronutrient. If it shows an optimal or high level, consider omitting it for the next six months. Also, if soil analysis shows high levels of micronutrients, consider omitting the micronutrient, especially if the leaf analysis also shows high levels. However, if the soil micronutrients are high, but leaf analysis shows low levels, it means those micronutrients are not available to the plant. Keeping the soil pH around 5.8 to 6.5 will ensure the micronutrients are readily available in the soil.

Davie Kadyampakeni is an associate professor, and Alisheikh Atta is a postdoctoral research associate, both at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Citrus Research and Education Center in Lake Alfred. Muhammad Shahid is an assistant professor at the UF/IFAS North Florida Research and Education Center in Quincy.