How to Handle Extended Flowering in HLB Trees

By Tripti Vashisth

University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) flower bud induction advisories for 2024–25 started on Nov. 25. The advisories will be posted bi-weekly until March 2025. The goal of the advisories is to provide growers and production managers with a complete overview of flowering prediction. Every advisory will aim to deliver recommendations for that period and steps needed to prepare for the flowering season, such as when to begin or stop PGR applications, fertilization, irrigation or sprays for disease and pest management.

A weak La Niña is predicted for this winter and spring (2025). This means Florida will experience temperatures warmer than normal, and rainfall will be lower than normal. Drought conditions are also likely to develop late in the winter and early spring as numerous fair and warm days are anticipated. Overall, we are in for warm and dry winter weather! Under these conditions, enough hours below 68 degrees are likely to accumulate to induce an economic level of flower buds, but intermediate warm periods during the winter can lead to multiple flower cohorts and a very prolonged bloom. 

Cool weather stops growth and then promotes induction of flower buds. A warm spell can then initiate differentiation, which after sufficient days of warm temperatures will lead to bloom. Trees will be very vulnerable to growth stimulation by a warm period after they accumulate 300 to 400 hours of cool temperatures if soil moisture is adequate. Currently, citrus-producing regions have low flower bud induction, which is low accumulation of inductive hours (temperatures below 68 degrees). Management of flower bud induction is limited at the low induction level. 

Here are some management considerations for HLB-affected trees:

• Do not drought stress HLB-affected trees
• Do not use flower-enhancing fertilizer for HLB-affected trees
• With current weather conditions and predictions, gibberellic acid (GA) spray to suppress early flowering is advisable, especially if the crop has been harvested in December. Suppressing early flowering will synchronize flowering and will improve leaf production (thus, better source to sink ratio). Better canopy equals better fruit production on HLB-affected trees. Do not spray GA after Jan. 1 to manage flowering.

Tripti Vashisth is associate center director and associate professor at the UF/IFAS Citrus Research and Education Center in Lake Alfred.

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