The post-harvest stage in cherry orchards represents one of the most critical periods for the crop’s future productivity.

After a season of high physiological demands, the plants must recover their metabolic balance and rebuild their reserves, a fundamental process to ensure adequate floral induction and differentiation, as well as future homogeneous budbreak and flowering, and consequently, to achieve the maximum productive potential of the orchards.

In this context, management practices during this period, in terms of preventing any abiotic stress, have established the application of sunscreens as a highly effective technical strategy. Their mechanism of action works primarily at the physiological level, preventing the premature closure of stomata, which play an essential role in transpiration, the plant’s temperature regulation, and the absorption of carbon dioxide during photosynthesis.

When solar radiation is excessive, temperatures rise above optimal ranges and relative humidity drops sharply, increasing plant transpiration due to an increase in vapor pressure deficit (VPD). According to data presented at the 10th International Cherry Symposium in Washington, D.C., by Avium’s research and development department, this optimum is achieved with temperatures of 23°C and relative humidity of 60%, ideal conditions not observed during the post-harvest period when the majority of cherry production materials are stored.

If the plant is unable to meet this water demand, an increase in abscisic acid (ABA) occurs. ABA is a key plant hormone in regulating the stress response, causing stomatal closure to prevent dehydration in response to atmospheric water demand.

This forced closure generates an increase in leaf and plant temperature, a reduction in photosynthesis and therefore carbohydrate synthesis, in addition to interacting with current metabolic processes such as floral induction and differentiation.

This directly impacts a lower accumulation of carbon reserves, affecting the orchard’s productive potential for the following season.

Throughout seasons of field studies and monitoring, Avium’s Research and Development department has demonstrated that orchards treated under this program exhibit a higher concentration of carbon and nitrogen reserves in the spurs during winter, impacting the orchards and resulting in better bud break, greater bud fertility, and a more stable productive response.

Generally, the use of sunblocks is especially relevant in orchards established on less vigorous rootstocks, or in production units with limited annual vegetative growth.

A balanced orchard should exhibit an approximate annual growth of 50 to 70 cm, associated with an appropriate ratio between fruit load and vegetative mass. It is important to emphasize that a large orchard does not necessarily correspond to a vigorous orchard, since vigor is measured based on growth recovery and annual vegetative response.

In addition to vigor, factors such as geographic location, sun exposure, frequency of heat waves, and soil water availability play a determining role when deciding to implement this tool. In seasons marked by high temperatures and drought conditions, the use of sunblocks becomes a valuable technical support for reducing the impact of abiotic stress.

It is worth noting that this practice must always be accompanied by a proper irrigation schedule, adjusted to the soil and climate conditions of each orchard. Efficient irrigation remains the most direct and effective tool for preventing water stress problems, while sunblocks complement this management by reducing the heat load on the plant.

In practice, field experience has shown that kaolin-based formulations (95% kaolin in the formulation), applied at concentrations between 2.5% and 3%, reduce leaf temperature during periods of peak radiation, promoting greater stomatal conductance during critical times of the day. This results in a more physiologically active plant, capable of maintaining its metabolism even under restrictive environmental conditions.

It is recommended to repeat applications at intervals of 25 to 30 days, depending on foliage growth, extending from late spring to mid-summer. Two to three applications in total should be made during the period of highest radiation and weather conditions.

In recent years, colorless sunscreens have also emerged, representing an interesting alternative for applications from pre-harvest to post-harvest. These formulations, in addition to reducing the incidence of sun damage to fruit, have shown positive effects in decreasing pedicel dehydration and maintaining fruit quality parameters during post-harvest.

For transparent “filters” that are intended as an alternative to sunblockers, it is suggested to make consecutive applications with intervals of no more than 14-15 days between each application.

Additionally, several studies have evaluated the incorporation of additives into conventional applications, such as seaweed extracts (primarily Ascophyllum nodosum), amino acids, and osmoprotective compounds like proline, which enhance the plant’s response to heat and water stress from a biochemical perspective.

These supplements have been shown to maintain better leaf thermal stability, optimize metabolic activity, and promote the accumulation of reserves. The most opportune time to begin applying sunscreens is immediately after harvest or during the following week.

Since January is a critical period for flower differentiation in central Chile, it is essential to maintain cherry trees under conditions of thermal, water, and metabolic equilibrium during this stage. Avium’s Irrigation and Climate Department has determined that by January 10th, 50% of the seasonal stress has typically accumulated, often meaning this strategy is implemented too late. In this regard, the integration of sunblocks, along with proper irrigation, nutrition, and canopy management, starting immediately after harvest (“immediate post-harvest”), strengthens the orchard’s resilience and optimizes its performance both in the current season and in future seasons.

In this sense, an indicator for recognizing critical environmental stress is the Stress Index (SI), an objective measure that relates ambient temperature and relative humidity, providing numerical support for the data. This index is calculated using the following formula:

Data is recorded from October to April each year, allowing for comparison of each zone with historical data and verification of its current state of environmental stress.

An analysis of the environmental stress rate for the central zone reveals the following:

Fig. 1. ESR rate for the central zone of Chile measured from October to April each year.

Note that the IE rate increases steadily from week 49-50, indicating that the plants are already being affected by this indicator, which is directly related to VPD (Vapor Pressure Deficit).

This means that actions or strategies to prevent the harmful effects of environmental stress should begin as early as December to avoid impacts on the plants and maintain metabolic status. Starting programs in January is likely too late for the desired effect.