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Protected-cultivation grapes (poly-cover)

Protected cultivation of grapes uses porous polymer covers (poly-covers or rain covers) installed over the trellis to shield the canopy and developing bunches from rain, hail, birds and temperature extremes. The technique has been developed for and increasingly adopted by table-grape growers in western India.

Principle

Excess water on berries during ripening promotes splitting, downy mildew and bunch rots and lowers sugar accumulation, while hail and bird damage cause direct physical loss. Air-permeable polymer covers exclude rainfall while preserving canopy ventilation, allowing growers to push harvest into pre- or post-monsoon premium windows and reduce reliance on prophylactic fungicide sprays.

Implementation

Standard installations mount a tunnel or saddle-shaped polymer film over each row, supported by additional cross-arms on the trellis. Covers are placed before the critical ripening period and removed after harvest to maintain pruning access. Material selection balances UV stability, light transmission and air permeability; commercial laminated PE films and woven net-films are both used. Drip irrigation, deficit irrigation during ripening and double-cycle pruning (Grapes Pruning Back Foreward) are complementary practices.

Adoption context

ICAR-NRC Grapes Pune, established in 1997 as the national centre for grape research, develops and validates protected-cultivation protocols. Adoption is concentrated in the Nashik, Sangli, Solapur, Pune and Satara belts of Maharashtra, where unseasonal rain and hail in the pre-harvest window cause repeated heavy losses on Thompson Seedless and its mutants.

Limitations

Capital cost is high relative to traditional pandal trellises, and films require periodic replacement. Excessive cover area or poor design can also trap heat and humidity, encouraging powdery mildew. Coverage decisions are therefore often made block-by-block based on weather forecasts and target markets.

See also: Grapes Pruning Back Foreward.

References

  1. ICAR-NRC Grapes Pune institutional portal.
  2. About NRC Grapes Institute.