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Gibberellic acid (GA3) foliar use

Gibberellic acid (GA3) is a diterpenoid plant hormone applied as a CIB&RC-registered plant growth regulator. Although gibberellins occur naturally in all higher plants, exogenous application at very low concentrations elicits strong responses, including stem elongation, dormancy breaking, parthenocarpic fruit set and reduction of flower and fruit drop.

Composition

Common Indian formulations include:

  • GA3 0.001% L (e.g. Pro-Gibb): ultra-dilute liquid for foliar spray
  • GA3 4% EC and GA3 20% SP: concentrated formulations that are diluted before use
  • GA3 90% TC: technical grade for further formulation

The active ingredient is fermented industrially from Gibberella fujikuroi. All commercial formulations require registration with the Central Insecticides Board and Registration Committee.

Mode of action

GA3 binds to GID1 receptors in the plant cytosol, triggering the degradation of DELLA repressor proteins and releasing transcription of genes for cell elongation, cell division, alpha-amylase production in germinating seeds, and reproductive transition. The effective concentration range is in the parts-per-million regime; doses above the active window cause excessive internode elongation, lodging and brittle stems.

Target use and dose

  • Grapes: 30-50 ppm at 50% bloom for berry elongation and bunch loosening
  • Chilli: foliar spray at 1-2 g/acre during the vegetative-to-flowering transition; 10-50 ppm to reduce flower drop and to revive shoot tips after sucking-pest damage
  • Mango: 20-50 ppm for off-season flowering
  • Sugarcane: 50-200 ppm for internodal elongation
  • Tomato, brinjal: 5-20 ppm for fruit set under heat stress
  • Seed dormancy: 100-500 ppm soak for poppy, rice and other dormant seeds

GA3 is sensitive to direct sunlight and high temperature; sprays are applied in the early morning or evening.

Safety and regulatory status

CIB&RC-registered with crop-specific labels. Non-toxic to humans and pollinators at field rates; no fixed pre-harvest interval at label doses.

See also: Ethephon Pineapple Flowering, Mepiquat Chloride Cotton, Biostimulants Amino Acid Seaweed, Cotton Biostimulant Flower Retention.

References

  1. Gibberellic Acid: The Growth Awakener of Plants. Peptech Biosciences.
  2. Nova GA CIB&RC Approved Gibberellic Acid. Kaybee Bio-organics.