Supporting Peach Growers with a Phenological Approach for Best Management Practices

Results and discussion

Phenological stages transition

We evaluated a total of 1,258 buds including floral and vegetative buds through daily observations from three commercial peach cultivars, which come from 23 sampling dates from Chilton AL, starting on September 2022 until March 2023. In total, it was observed that only 884 bud breaks occurred distributed as 584 floral bud breaks, and 300 vegetative bud breaks. Harvester was the earliest cultivar in bud breaks followed by Rubyprince and Redglobe respectively (Table 1). For the season 2022 - 2023 bud breaks started on January 2, 2023, and finished on March 20, 2023.

Table 1. Total bud breaks per cultivar and the early, late, and average date of bud breaks (BB). 

We used statistical procedures to establish correlations between variables such as bud position, bud type, and the days to reach the dormancy release among cultivars. Regarding the dormancy releases in floral buds, there were significant differences between the Harvester and Redglobe cultivars (p < 0.05), but there were no differences between Harvester-Rubyprince and Redglobe-Rubyprince as shown in Table 2.

Table 2. P-values for the comparison among peach cultivars.

Significant differences between the Apex and Base positions in floral bud breaks were found (p < 0.05), while Apex-Mid and Base-Mid positions were not significant Table 3.

Table 3. P -values for the comparison between bud positions (A: Apex, M: Mid, and B: Base).

Furthermore, the interaction between Cultivar and bud type was significant as Table 4 shows.

Table 4. P values for cultivars, bud position, bud type, and the interaction between cultivars and bud type.

The frequency of floral and vegetative bud breaks was determined as the number of dormancy releases through time for each cultivar (Fig. 1).

Harvester was the cultivar with the highest frequency of floral breaks followed by Redglobe and Rubyprince. Most of the floral and vegetative bud breaks were observed during late February and early March 2023, considering that the initial date of the experiment was September 1, 2022. The days with the highest frequency of bud breaks are shown in Table 5.

Table 5. Summary of the days (From September 1 until bud break date) with the highest frequency of dormancy releases.

The total chilling hours were calculated for each of the cultivars during the earliest, late and average floral dormancy release period (Table 6).

A minimum of 466 and a maximum of 864 chilling hours were accumulated for all the cultivars evaluated, ranging from the earliest until the latest bud breaks. The calculation of heat requirements for all stages is still in progress.

Table 6. Total chilling hours accumulated during the dormancy release.

Heat and Chilling Requirements

A significant high correlation among all the chilling models was found for the season evaluated; GDD was negatively correlated with all the chill accumulation models (Table 7). These results suggest that any of the models can be used for chill accumulation combined with GDD.

Table 7. Pearson correlation coefficients for chilling and GDD models for 2022-2023 years.

Model Integration for Chill and Heat Requirements

Using 3D graphs the chill and heat requirements were combined to evaluate the distribution of budbreaks in the vegetative and floral buds. An example of the Weinberger model is presented as a result (Figure 2), these 3D graphs explained the negative correlation found between chilling and heat models. Therefore, while the chilling requirements increased the heat requirements were less, and vice versa, thus the percentage of budbreak was in function of this correlation, and this tendency was observed for both bud types.

Influence of climate variability on phenological stages

Once the budbreak stage was determined for each cultivar, the floral stages were characterized for the cultivars evaluated (Figure 4), according to the classification described for peach growth stages in Alabama and Southeastern Peach Growers’ Handbook (Hortan and Johnson, 2005, Coneva, 2022). The evaluation of chilling requirement in a progressive methodology allowed analyze the effect of the different winter scenarios simulated in this experiment on the progression of floral bud. For the period evaluated (2022-2023), most of the buds reached the full bloom stage with a previous chilling accumulation in a range of 740 to 792 chilling hours, which confirm the relevance of the completion of chilling requirements for the floral progression until full bloom stage. Rubyprince’ was the cultivar with the best performance regarding to the progression of the stages including the full bloom. Most of the buds that reached the full bloom stage came from ‘Rubyprince’ cultivar.

Thermal requirements

In terms of heat requirements, the floral bud progression in the cultivars assessed needed between 425.5 to 777 GDD. Pink, first bloom, full bloom, and petal fall were the stages with the highest demand of GDD. Once samples reached the budbreak, they needed between 25 to 28 days during the season assessed. ‘Rubyprince’ was the most delayed cultivar in the floral progression, followed by ‘Harvester’ and ‘Red Globe’.

Table 1. Floral bud progression in terms of GDD  and days for each cultivar and season.