citrus greening

New Light Shed on HLB and Fertilization

Tacy Callies HLB Management, Nutrition

Small, lopsided fruit from greening-infected citrus tree
(Photo courtesy of UF/IFAS)

The effort to help huanglongbing (HLB)-impacted citrus trees has taken another step forward. A University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) study examined the relationship between fertilization, root health and fruit yield. Researchers focused on Valencia orange trees with HLB.

Associate Professor Davie Kadyampakeni led the effort at the UF/IFAS Citrus Research and Education Center.

The study, spanning multiple years and sites, had several goals. It aimed to assess changes in root density, understand HLB dynamics concerning root growth, and evaluate the impact of varied fertilization on fruit yield and juice quality.

“We wanted to test whether enhanced macro and micronutrient levels would restore root health and improve overall tree performance,” Kadyampakeni explained. “Roots play a pivotal role in nutrient absorption and overall tree vitality, so would the different nutrient inputs, in the face of HLB, rehabilitate the root health?” 

The study involved Valencia orange trees planted in 2012 and 2013. The macronutrients used were potassium, magnesium and calcium. The micronutrients were zinc, manganese, iron and boron. Those were applied through the soil or the trees’ foliage.

The team used soil core samplers and minirhizotrons for root sampling and monthly root growth assessments. 

Root growth patterns revealed fluctuations linked to citrus tree physiological processes. Growth peaked during seasons when the trees showed new shoot growth, flower formation and fruit formation.

Interestingly, the study observed a significant negative correlation between root growth and fruit yield. This suggests a trade-off influenced by the HLB-affected environment. 

“Fruit yields were optimized with elevated micronutrients, particularly through soil application, emphasizing the role of nutrient availability in promoting root growth and fruit yield,” Kadyampakeni said.  

The study also highlighted site-specific responses, indicating the need for customized fertilization approaches. While the change in fertilization did not impact juice quality, total soluble solids (TSS) differed between two research sites. TSS were higher on the Ridge compared to the Flatwoods near Clewiston, suggesting that one size doesn’t fit all.  

“The correlation between root health and fruit yield shed light on the complex factors in HLB-affected citrus trees,” Kadyampakeni said. 

This research adds to the understanding of root dynamics in HLB-affected environments. It also suggests that tailored fertilization strategies may lessen the impact of HLB and prolong the productive life of bearing citrus trees.  

The research was published in the journal HortScience. See the full article here.

Acknowledgment: The Citrus Research and Development Foundation provided funding for the research.

Source: UF/IFAS