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Blackberry with blind buds

Gibberellic Acid Overcomes Lack of Chill in Blackberry

Blackberry cultivars developed in Arkansas are popular but not well adapted to Florida conditions. Lack of winter chilling (temperatures between 32 and 45 F) causes poor and erratic budbreak in blackberry and limits consistent yields in Florida. Cumulative chilling hours in central Florida were 165-130 hours in the two Florida growing seasons of the experiment, while the cultivars tested are estimated to need 300-900 hours depending on cultivar. Typical  budbreak in Florida is only about 30% of potential buds. Gibberellic acid (GA3) is a plant hormone that affects plant growth and has been used with some plants to overcome lack of winter chilling. Researchers at UF wanted to see if GA would help blackberries to be more productive in Florida.


‘Natchez’, ‘Navaho’, and ‘Ouachita’ blackberry cultivars growing in central Florida were treated with a single spray application of water or GA3 (ProGibb LV Plus, Valent Biosciences). The plants were dormant at application in late December to late January over two years, and growth and yield were measured.


GA3 advanced budbreak by 12 to 82 days, flowering by 4 to 20 days, and fruit ripening by 0-15 days. Early season yields were increased by 83-276% in two consecutive growing seasons, and total season yield was increased by 60% in the second growing season. Yield response did vary with cultivar, with ‘Ouachita’ responding the best and ‘Natchez’ the worst. These results suggest GA3 can be used to induce earlier as well as total fruit yields. However, weather following application of GA3 may be important because of the risk of freeze damage to earlier buds. Also, the best rate of GA3 to apply varies by cultivar and further testing is needed to determine optimum rates for each cultivar.


Agronomy 2020, 10, 1327. Exogenous Gibberellic Acid Advances Reproductive Phenology and Increases Early-Season Yield in Subtropical Blackberry Production. Syuan-You Lin and Shinsuke Agehara.

More information on growing blackberries in Florida.

2 Comments on “Gibberellic Acid Overcomes Lack of Chill in Blackberry

  1. I have 2 acres of u pick Prime Ark Freedom. Could you venture a guess of what rate I should apply to this variety? Since it is a primocane, could it affect yield negatively to try it?

    • Primocane varieties react a little differently to GA. UF/IFAS specialist Dr. Agehara says that they have tested GA on primocane varieties and it was very effective in inducing budbreak, but it caused flower abortion and reduced yield. Blackberry is still not listed on the product label for GA because of the potential for phytotoxicity (flower abortion) on ‘Natchez’ and primocane varieties. Its commercialization for blackberry may not happen. In more recent studies they found some defoliants are equally effective in budbreak induction as GA but with no phytotoxicity. Urea was the cheapest and most effective defoliant. More details when that paper is published. A December application was effective in promoting fruit earliness but February application is more effective in maximizing budbreak. The current recommendation for Urea is: Timing: Feb 20th for ‘Natchez’ (or soon before natural budbreak for the variety)
      Application rate: 10% solution at 200 gallons per acre (167 lbs of urea in 200 gallons of water). As always when trying a new experimental technique, test on a small area first.