Thinning Response of ‘Redhaven’ peaches to 1-aminocyclopropane carboxylic acid (ACC)

Peach trees bear an abundance of flowers which produce a surplus of fruit that the tree is unable to support. A self-regulatory mechanism enhances the abscission of immature fruitlets leading to a reduced fruit load, but this is often insufficient to achieve fruit of marketable size. Supplementary manual fruit thinning is typically required to optimize economic fruit load. This 2-year study investigated the response of Redhaven peach trees to sprays of 300 and 600 mg L-1 1-aminocyclopropane carboxylic acid (ACC) during the phenological stages of full bloom, shuck split and ~20-mm fruitlet diameter. The objective was to determine the efficacy of ACC on fruit set, fruit size and yield at harvest, and the amount of hand thinning required at ‘June drop’. Although the response to ACC varied between the two years, 600 mg L-1 ACC spray at full bloom (2018) and ~20 mm fruit size (2019) reduced fruit set, the need for 59–66% of hand-thinning, and crop load. Treatments also had varying but significant effects on leaf yellowing and leaf drop when measured shortly after application. ACC reduce total yield and number of fruit per tree in both study years, and increased fruit weight in 2019. Overall, peaches were responsive to ACC at a range of timings from bloom to ~20 mm fruit size. This study enhances our understanding of ACC on fruitlet abscission of peaches and is one of few studies to demonstrate the effectiveness of a chemical fruitlet thinner for peaches.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author