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.