Evaluation of Blossom Thinning Spray Timing Strategies in Apple

Abstract

In the eastern USA and several other apple-growing regions, apple blossom thinning using lime sulfur is a relatively new crop load management strategy. This study sought to evaluate how application timing of lime sulfur + stylet oil blossom thinning sprays would influence thinning efficacy and crop safety of ‘Gala’ apples. This project occurred at two locations in the USA, Winchester, Virginia, and Mills River, North Carolina, during the 2019 growing season. Two main timing strategies were assessed: (1) model-guided sprays with the pollen tube growth model (PTGM), (2) fixed spray intervals with the first spray applied at a specified percentage of open bloom (20% vs. 80%), and the second spray applied at a reapplication interval (48 h vs. 72 h). Model-guided and 20% open bloom + 48-h treatments reduced fruit set and increased fruit weight, diameter, and length at both sites. Treatments with a delayed first spray at 80% open bloom or a more extended second reapplication of 72 h were generally ineffective. There was no conclusive evidence that lime sulfur + stylet oil blossom thinning spray timing influenced russet incidence/severity or leaf phytotoxicity. This study demonstrated that effective and safe blossom thinning can be obtained from applying two sprays at 20% open bloom and 48 h thereafter or using the PTGM.

Rootstock effects on bitter pit incidence in ‘Honeycrisp’ apples are associated with changes in fruit’s cell wall chemical properties

“…Fruit quality was assessed immediately after harvest. At each assessment, 5-10 apples were used from each tree to measure fruit diameter, weight, firmness and total soluble solids (TSS) according to methods described previously by ( Allen et al., 2021 ). Fruit firmness was recorded for the sun and shade side of each fruit using a Fruit Texture Analyzer (FTA, QA Supplies, Norfolk, VA).…”

Development of a GIS-based Autonomous Soil Drilling Robot for Efficient Tree Cultivation and Orchard Planting

“…There are numerous automated harvesting robot prototypes for orchards [8][9][10][11][12]. Additionally, there are also studies in the literature on robotic tasks like thinning [13], spraying [14], pruning [15], and mobile navigation [16] in orchard environments. Every orchard management operation listed above requires a mobile platform in order to move the actuators around the orchard.…”

Evaluation of Computer Vision Systems and Applications to Estimate Trunk Cross-Sectional Area, Flower Cluster Number, Thinning Efficacy and Yield of Apple

“…Precision chemical thinning is the sequential application of chemical thinning sprays, guided using computer models to adjust the rate and timing of chemical application. The models include the pollen tube growth model (PTGM) to time blossom thinning spray applications precisely [14][15][16][17]. This model requires a visual observation of the percentage of open blossoms.…”