A newly published study suggests that the use of individual protective covers (IPCs) followed by monthly applications of homobrassinolide (HBr) after IPCs are removed is beneficial. The two-step approach can help young mandarin trees stay healthier longer and produce more fruit in Florida’s HLB-endemic environment.
The study, “Combining Individual Protective Covers and Homobrassinolide Treatment Prolongs Tree Health and Increases Fruit Yield in Young Tango Mandarin Trees Under Endemic HLB,” was published in the journal Agronomy. Saoussen Ben-Abdallah and Fernando Alferez of the University of Florida Institute of Food and Agricultural Sciences Southwest Florida Research and Education Center conducted the study.
Researchers evaluated young Tango mandarin trees grafted onto either sour orange or US-942 rootstocks. Trees were protected with IPCs for their first three years in the field to keep out Asian citrus psyllids, the insects that spread HLB. After the covers were removed, half the trees received monthly foliar sprays of HBr, a plant hormone already registered for commercial citrus use in Florida.
IMPROVED TREE HEALTH
The study found that IPCs delayed HLB infection by six to nine months after the covers were removed. Trees that received both IPC protection and HBr sprays developed larger canopies, especially on sour orange rootstock. Trees receiving both treatments maintained better overall tree health than trees without the combined treatment.
BETTER YIELD
One of the biggest benefits for growers was yield. Trees protected with IPCs had less preharvest fruit drop and produced more fruit than unprotected trees. On sour orange rootstock, adding HBr after IPC removal provided an additional yield boost. Fruit quality — including sugar content, acidity, peel color and fruit size — remained similar across all treatments, showing that the extra production did not come at the expense of fruit quality.
ROOTSTOCK ROLE
The researchers also found that HBr activated genes involved in the tree’s natural defense system, helping stimulate systemic acquired resistance. This response was strongest and occurred earlier in trees on sour orange rootstock, suggesting rootstock selection may influence how well the treatment works.
PRACTICAL APPROACH
For citrus growers, the findings point to a practical strategy for establishing young groves under heavy HLB pressure. IPCs remain the first line of defense by preventing psyllid feeding during the most vulnerable years. Once the covers are removed, HBr applications may help maintain tree vigor, slow disease progression and extend productivity until trees become large enough for additional management tools, such as oxytetracycline trunk injections.
The researchers conclude that integrating physical protection with immune-stimulating treatments offers a promising approach to improving the survival and productivity of young citrus trees in Florida’s HLB environment.
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