Apricot (Prunus armeniaca L.) production in Texas is limited by inconsistent and overall poor yields due to spring frost and loss of hardiness in buds associated with erratic temperature swings in late winter/early spring. Several plant growth regulators (PGRs) were evaluated for improving yields. PGRs were applied in the fall and spring to assess their potential for mitigating floral bud injury, improving bud hardiness, enhancing fruit set, and improving fruit retention rates. Two-year-old ‘Wenatchee Moorpark’ trees on ‘KRYMSK-1’ rootstock, spaced at 1.33 by 3.33 meters were used with a randomized complete block design with five single-plant replications. Fall applications were made at approximately 50% natural leaf fall of Ethephon at rates of 100, 200, and 300 mg/L-1, Accede (ACC) at rates of 500, 1000, and 1500 mg/L-1, and ProTone (S-ABA) at rates of 500 and 1000 mg/L-1. Following defoliation of the trees, white latex paint was also applied as a treatment to the entire canopy and trunk of dormant trees. Spring treatments aimed at improving fruit set were applied during full bloom and included Promalin (GA4+7, 6-BA) at rates of 1.17 and 2.34 L/ha-1, and ReTain (AVG) at rates of 889 and 1,778 mg/L-1. Additionally, evaluations were conducted on combination treatments of fall and spring applications. These treatments included Ethephon+Promalin+Latex; Ethephon+ReTain+Latex; Accede+Promalin+Latex, and Accede+ReTain+Latex, which were applied at the highest concentrations for each product evaluated individually in this study. Differential Thermal Analysis (DTA) was carried out on the 15th and 16th of February 2025 using 5 floral buds per tree as sub-samples. LT50 found Accede at 1500 mg/L-1 significantly improved bud hardiness by 4.67°C relative to the control. Additionally, treatments of Accede+Latex, Accede+Promalin+Latex, and all three combination treatments of Ethephon delayed floral bud development relative to control. However, Ethephon produced significant gummosis and visible injuries, whereas Accede produced negligible gummosis. Fruit set, as assessed by counting fruit on 50.8cm lengths of standard sample shoots, was improved using the highest concentration of ReTain (AVG). The mean fruit number increased from 1.2 for the control, to 5.0 for AVG, at P= 0.0002, occurring after exposure to temperatures below -4°C on March 19th. The results from this and future years of this trial are anticipated to assist in improving the feasibility of commercial apricot production within Texas and similar environments.
