Effect of Hydrogen Cyanamide on Flower Production of ‘AU Golden Sunshine’ and ‘AU Gulf Coast Gold’ Kiwifruit

Abstract

The Actinidia chinensiscultivars, ‘AU Golden Sunshine’ and ‘AU Gulf Coast Gold’ produce heavy crop loads of large, commercially acceptable kiwifruit in central Alabama. However, due to fluctuations in annual winter temperatures, these vines may not always receive sufficient amounts of chilling hours or units or portions they require to break bud and flower effectively. When these vines do not receive 700–900 chilling hours, they can exhibit nominal and intermittent bud break and flowering. This leads to insufficient cropping and negative economic impacts for growers. Experiments were conducted over 2 years on ‘AU Golden Sunshine’ and ‘AU Gulf Coast Gold’ to determine the effectiveness of the dormancy breaking chemical, hydrogen cyanamide (HC). Applications of HC were made ~28 (1 Feb.) and ~14 (15 Feb.) days before natural bud break to assess the effect on timing of application. Bud break was advanced in response to HC applications, with earlier applications causing bud break to occur earlier. In year one, vines receiving applications ~14 days before natural bud break showed increased bud break and flowering intensity as well as a reduction of lateral flower buds over the vines treated at ~28-day before natural bud break. The nontreated controls had the fewest lateral buds throughout the study. During year two, all vines were injured by a late frost event that occurred 7 Mar. 2019. Vines receiving the earliest HC applications were damaged the most, followed by the vines receiving the second HC application, which led to reduced flower production compared to nontreated vines. Control vines had the greatest number of floral shoots after the frost event because they were the last to experience bud break. Hydrogen cyanamide may be a beneficial tool to growers experiencing lower than normal chilling, however caution is advised due to the possibility of late spring frost.