Best practices for using ReTain to manage apple harvest

New technical manual and training offered by Valent summarized applications for production regions across the country.

Cover of manual
ReTain technical manual by Valent Biosciences.

ReTain (aminoethyoxyvinylglycine or AVG) is one of several very useful tools for managing apple harvest. It is a plant growth regulator (PGR) produced by Valent Biosciences. Recently, the company offered updated recommendations and a training for service providers on the best practices for using ReTain for apple harvest. In addition, they published a thorough Technical Manual for ReTain available for free online, detailing the product specifications and recommendations for application in regions across the world. Below is a summary of the recommendations.

ReTain mode of action

Both ReTain and SmartFresh (1-MCP) are PGRs used for managing apple harvest. Both act by interacting with ethylene, the hormone that stimulates ripening.

  • ReTain (AVG, made by Valent) – inhibits ethylene biosynthesis
  • SmartFresh (1-MCP, made by Harvista) – inhibits ethylene action

The ethylene pathway is autocatalytic. A pathway is called autocatalytic if one of the reaction products is also a catalyst for the same or a coupled reaction. In other words, once ethylene is produced, it initiates the production of more and more ethylene. A good metaphor for this is a runaway train—once started, it is hard to slow down.

The effects of ReTain depend on four key things. Below are the recommendations for each:

  1. Rate:
    • 1-2 pouches (333-666 grams per acre)
  1. Time:
    • 30 days before harvest for maximum effect.
    • 7-14 days before harvest for less impact on color, but also less effect on other parameters.
    • Application closer to harvest will have less impact on delaying harvest.
  2. Variety:
    • Sensitive: Gala, Honeycrisp, Jonagold are more sensitive (same rate will delay harvest more)
    • Normal: Reds, Fuji, Goldens
    • Harder: Granny’s, Braeburn
  3. Crop load:
    • Lighter crop load starts ethylene production earlier
    • Don’t apply high rates to high crop load

NAA in combination with ReTain

NAA is another PGR that can be used to manage apple harvest. NAA is an auxin that prevents abscission but can accelerate maturity. Used with ReTain, it can delay maturity and drop.

  • Always tank mix or put ReTain on before
  • Use at least half a pouch
  • Program 1: ReTain at three weeks before harvest plus PoMaxa/Fruitone 2-4 ounces at one week before harvest
  • Program 2: Tank mix at three weeks before harvest

Best conditions for ReTain applications

Conditions are critical for the effective use of ReTain. Below are the recommended conditions:

  • Temperature/humidity: A cool fruit surface and internal temperature are best; slow drying conditions (early morning applications are ideal).
  • Rain: 6 hours of drying time is ideal
  • Adjuvant: 0.05-0.1% organosilicone (6.5-13 fluid ounces 100 gallons)
  • Water volume: 100 gallons per minute, pH 6-8
  • Phytotoxicity – There is some phytotoxicity (leaf and fruit finish) associated with the organosilicone adjuvant; potentially a negative interaction with Captan, Zinc, other nutrients; recommended seven days separation between applications.

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