Effect of a Late Spring Application of Hydrogen Cyanamide on High-Chill Peaches

Due to a record low chilling accumulation in the winter of 2016-2017, many high-chill peach cultivars displayed almost no budbreak by mid-April of 2017 in central Georgia, USA, where budbreak usually occurs around mid-March. In this study, nine of these peach cultivars were used to study the effect of a late spring Dormex spray application (April 13, 2017) on subsequent budbreak, year-end cumulative vegetative growth, and following-season yield. Dormex was found to have strong stimulating effects on lateral budbreak, but little effect on terminal and floral budbreak. It also had apparent phytotoxic effects on lateral, terminal and floral buds, and growth. The effects varied among genotypes, tree ages, and shoot types. The peak of the effects occurred two weeks post-application. Most floral buds abscised before they swelled. Between Dormex-sprayed trees and unsprayed controls, there was no significant difference in the number and average length of the new lateral shoots by the end of 2017, nor in the number and weight of the fruit harvested in 2018. In conclusion, our data showed a late spring Dormex spray application stimulated earlier lateral budbreak and caused some level of phytotoxicity to all types of buds and new growth, but had little impact on flower budbreak, fruit set, year-end vegetative growth, or following-season yield. These findings provide useful information for growers, considering the need for spraying dormancy-breaking compounds when faced with insufficient chilling.