2017 ASHS Annual Conference

Peach trees have a chill hour requirement that is satisfied when they are exposed to temperatures between 0 °C and 7 °C. Over recent years, peach trees have been able to accumulate fewer chill hours and therefore, flowering occurs sporadically and over a longer period. This leads to less profitable harvests and protracted harvest periods. Hydrogen cyanamide (HC) is a plant growth regulator used to break bud dormancy when chill hour requirements for peach trees have not been reached. Effectiveness of application will depend on concentration of HC used and number of chill hours accumulated at the time of application. The objective of this study was to determine the most effective rate and timing of application of HC in inducing budbreak in ‘Harvester’ peach trees. Applications of HC were made with a blast sprayer to ‘Harvester’ peach trees, previously treated with ethrel, at rates of 0.5 %, 1.0 %, 2.0 %, and 4.0 % when trees received 70 %, 80 %, and 86 %, of the chill hour requirement. One treatment received ethrel at the recommended rate and HC while the control treatment received neither HC or ethrel. Four one-year old shoots per tree 50 cm – 60 cm long and 1m - 2m from the ground were selected and flower buds were rated periodically according to developmental stage. High rate of HC application (4%) caused bud break to occur approximately 7 days earlier than other HC treatments. Peach trees that received HC at the 4% rate and applied after trees received natural chill of 86% of the chill hour requirement broke dormancy sooner and reached fruit set earlier than did those that received fewer natural chill hours. Generally, trees that received the highest chill hours exhibited more optimal proportion of fruit to leaf surface area. Hydrogen cyanamide is effective in breaking dormancy in peach trees that are deficient in chill hour accumulation; however, even high application rates are ineffective when chill hour accumulation is substantially deficient.