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GA3 elongation spray on Thompson Seedless cluster Photo: Sharath G. · Pexels License · source ↗

GA3 berry thinning and elongation in grapes

Gibberellic acid (GA3) is the most economically important plant growth regulator (PGR) in Indian table-grape production. For seedless varieties such as Thompson Seedless (Grapes Thompson Seedless) and its mutants, GA3 is sprayed at three different stages to perform three different physiological jobs: cluster (rachis) elongation, berry thinning, and berry sizing. ICAR-NRC Grapes Pune publishes a stage-wise PGR schedule under Technical Bulletin 23.

Principle

Seedless berries normally lack endogenous gibberellins because the developing seed - their natural source - aborts. Exogenous GA3 substitutes for the missing seed signal, driving cell elongation in the rachis and pedicel and cell expansion in the berry. Timing is critical: too early causes phytotoxic damage, too late gives no response.

Procedure (Thompson Seedless schedule)

ICAR-NRCG's recommended stage-wise spray schedule:

  • Pre-bloom elongation spray (10-15 cm rachis stage, around 5-10% cap fall): GA3 10-15 ppm whole-cluster dip or directed spray; elongates the rachis and pedicel, producing loose well-shouldered bunches and reducing the need for hand thinning.
  • Berry thinning spray (3-4 mm berry, full bloom / immediately after fruit set): GA3 30-40 ppm cluster dip; aborts excess weak berries through pedicel collapse, leaving 90-120 well-spaced berries per cluster.
  • Berry sizing sprays (6-8 mm and 12-15 mm berry): GA3 40-50 ppm cluster dip; expands berry diameter to 18-22 mm to meet the export grade standard.

Total dose used in a season is around 35-40 g a.i./acre. CCC (chlormequat) at 1000-1500 ppm is sometimes co-applied for shoot growth control during the foundation phase but is a separate PGR job.

Where it applies

GA3 spraying is standard on all export-grade seedless cultivars across Nashik, Sangli, Solapur, Pune, Satara and the north Karnataka belts. Seeded cultivars such as Anab-e-Shahi do not respond well to GA3 sizing and may show berry shatter; lower doses are used only for elongation.

Limitations

  • Phytotoxicity: high GA3 doses on the leaf surface cause leaf curling and shoot crinkling.
  • Variety sensitivity: clones and mutants of Thompson Seedless respond differently; growers calibrate doses block-by-block.
  • Residue / MRL: GA3 itself is permitted at low residues by most importers, but accompanying CCC and copper sprays have stricter limits; growers must respect the EU MRL (Grapes Export Residue Mrl Europe) regime and record every spray on GrapeNet (Grapenet Apeda Traceability).

See also: Grapes Thompson Seedless, Grapes Pruning Foundation Fruit, Grapes Export Residue Mrl Europe.

Sources

  1. Use of Plant Growth Regulators in Grapes. ICAR-NRC Grapes Technical Bulletin 23.
  2. ICAR-NRC Grapes Pune institutional portal.