2019 ASHS Annual Conference

Fruit growth is limited early in the growing season by competition among fruit for available resources. By reducing the crop load, competition is lessened, and fruit growth can be maximized. Thinning is a common cultural practice used to remove fruit to reduce competition and potentially achieve larger fruit size and higher yield. The timing and intensity of thinning affects the efficacy of the treatment. The objective of this study was to determine which thinning time and intensity is most appropriate for Georgia peach growers. We evaluated the effects of three thinning times (at bloom, ~40 days after bloom (DAB), ~60 DAB) and two intensities (~15 cm or ~20 cm fruit spacing) for three peach cultivars (CaryMac, Springprince, and Juneprince) in 2017. No significant differences were observed among treatments for final yield, fruit weight, diameters, soluble solids content, nor titratable acidity. A late spring freeze paired with the substantial lack of chill hours in 2017 likely affected the responses seen in these cultivars. The study was repeated in 2018 using earlier thinning times (bloom, ~14 DAB, ~28 DAB) and the same two intensities for three cultivars (CaryMac, Summerflame, and Julyprince). In 2018 adequate chill hours accumulation occurred and Georgia did not experience a late hard freeze. The differences observed among treatments suggested that bloom thinning is not a viable option for Georgia growers and that it may be better to thin later to a higher intensity. In addition, we aimed to develop a model that could predict harvest dates and final fruit size/total yield based on chill hour accumulation, early spring temperatures, and a variety of field-specific parameters. We have observed a significant relationship between growing degree hour accumulation (at 30 days after bloom) and yield per tree. The goal of this model is to provide growers with an idea of what to expect that season and aid in their decision to thin.