Plant Growth Regulators (PGR)
Overview
- A tool to manipulate shoot, flowering, and fruit development.
Each class of PGR has a unique function, therefore PGRs cannot be interchanged for a desired effect.- Auxin
- Gibberellins
- Cytokinins
- Ethylene
- Strigolactones
- Brassinosteroids
- Plant response and efficacy of PGRs depends on the concentrations, plant health, nutritional and water status, and time of year.
Gibberellins (GA)
- Monthly GA applications (10 oz/acre) from September to January can improve the yield and reduce fruit drop.
- Alternatively, summer application of GA, July to October, can improve vegetative growth which can improve productivity.
- GA application slows the color change, a 2-to-4-month interval should be given between the last GA application and harvest.
- GA can enhance fruit set, therefore GA applications in March to May should be avoided.
Auxin
- 2, 4-D is synthetic auxin that can reduce the fruit drop in citrus.
- Timing is critical. If applied too late, it may not be effective, but if applied too early, its effect may fade.
- 2, 4-D (3 oz/acre) should be applied about 3 months before the anticipated drop.
- The application can be split in 2 or 3 applications to better cover the fruit drop period.
Resources
Florida Citrus Production Guide: Plant Growth Regulators
Use of Gibberellic Acid to Improve Health and Productivity of HLB-Affected ‘Valencia’ Trees