Climate variability is having negative effects on the phenology and physiopathology of sour cherries.

Increasing climate variability is affecting cherry production, particularly in high-elevation continental areas of Utah, where tart cherry (Prunus cerasus L.) is a strategic crop.

A recent study examined two critical aspects of orchard management: the occurrence of double fruits caused by summer heat stress and the reliability of temperature-based phenological models for predicting bloom. Both phenomena are closely linked to thermal dynamics and have direct economic consequences along the supply chain.

The issue of double fruits

The issue of double fruits is a physiological disorder involving the formation of two or more pistils within the same flower, leading to fused, misshapen fruits unsuitable for industrial pitting. By using mobile structures covered with plastic to induce controlled heat stress on mature trees at different post-harvest intervals, researchers were able to identify the window of greatest susceptibility during flower bud differentiation.

Treatments were applied weekly for nine weeks after harvest, and the incidence of double fruits was assessed the following year both on the trees and in mechanically harvested fruit. Results showed that heat stress imposed during the fifth week after harvest led to the highest incidence of double fruits, with levels more than three times higher than untreated controls in both experimental years.

Key findings and mitigation strategies

This suggests that carpel primordia differentiation occurs during this stage, similarly to what has been observed in sweet cherry, where temperatures above 30°C (86°F) during pistil formation significantly increase the frequency of double fruits.

Another key finding was marked year-to-year variability: one season showed substantially higher overall levels of doubling than the following one, indicating that, in addition to individual stress events, cumulative and preceding thermal conditions also play an important role.

From an applied perspective, identifying a critical window allows growers to concentrate mitigation strategies within a defined period, such as targeted irrigation or cooling techniques, thereby optimizing costs and benefits.

Climate change and phenological models

Climate change is also challenging the predictive capacity of traditional phenological models used to forecast bud development and bloom timing.

During the study, field data were collected across multiple locations over five consecutive years, comparing observed phenological stages with predictions from several temperature-based models: the Utah Model, Utah Modified, North Carolina, and Dynamic Model.

The analysis showed that the Utah Model still provides the best overall accuracy in predicting full bloom, with an average error within two days and a correct classification rate of 79%. However, model performance varied considerably depending on year and site, highlighting structural limitations of two-phase models (chilling plus heat accumulation) under non-stationary climatic conditions.

Limitations, improvements, and conclusions

In particular, milder winters and earlier springs alter the balance between chilling fulfillment and heat accumulation, weakening the assumption of a clear sequential transition from endodormancy to ecodormancy.

The study suggests potential improvements, including updating chilling requirement parameters, integrating farm-level microclimatic data, and developing more dynamic modeling approaches. In conclusion, the study defines a specific time window (between the 4th and 6th week after harvest) during which summer heat stress can lead to double fruit formation, compromising production.

It also confirms the value of phenological models as decision-support tools, while emphasizing the need to adapt them to evolving climatic conditions. Overall, temperature management emerges as one of the key factors in ensuring yield stability and industrial quality in tart cherry production.

Source: Moon, J. M. (2025). Temperature Effects on Fruit Doubling and Bloom Prediction in Tart Cherry. All Graduate Theses and Dissertations, Fall 2023 to Present. 589. https://doi.org/10.26076/0f3c-86ba 

Image source: Stefano Lugli

Andrea Giovannini
PhD in Agricultural, Environmental and Food Science and Technology - Arboriculture and Fruitculture, University of Bologna, IT

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