In everyday life, we are always trying to maximize time to be more efficient in all areas, making it a daily race that requires excellent time management. For instance, setting schedules for going to work, dropping kids off at school, where one has a window of time, a defined route to reach the destination at the right moment, and avoid getting stuck in traffic jams that usually occur in the mornings. Those who have children will understand these circumstances well and know that it’s a time management process that is pre-planned and timed every day.
You might be wondering, “What does this have to do with fruit cultivation or, in this case, specifically with cherry farming?” Well, in truth, there is not much direct connection. However, there is one similarity between both situations, and it relates to knowing the right time to act to achieve good results according to the set objectives.
This leads us to present some important aspects to consider when deciding the timing of dormancy breaker (DB) application, specifically the use of hydrogen cyanamide (HC) in mature cherry orchards.
Although this season doesn’t have a rush to harvest “early,” due to the different timing of Chinese New Year compared to the previous season, there are always conditions during each production period that do not follow a specific pattern and are rather multifactorial, making them difficult to predict. Therefore, it is crucial to establish the right application moments and define dates for DB sprays in general, in this case, using HC, to achieve the best response to the strategy and reach the desired productivity potential for each case.
From this point of view, as a “manual,” a significant part of the industry recognizes that post-harvest management starts the day after harvesting the last fruit. From that point onward, all measures must be taken to ensure proper flowering in the spring, which is primarily correlated with good carbohydrate accumulation.
Experiments
Since the 2020-21 season, work has been done to find the right application time for HC, and these trials were also conducted in the 2021-23 season with results that could help in making decisions based on the available information (Fig. 1).
The applications of HC were carried out in cvs. Santina and Lapins, both grafted on Colt rootstock, in an early zone in the Sagrada Familia commune, VII Region, Chile. For Santina, it was an analysis of the productive potential, as no load regulation strategy was applied for the research purposes. The sprays were conducted from 30.06.21 to 04.08.21 in both varieties, with applications every seven days in sectors without any HC treatment at 2%, resulting in six dates with plants treated with HC and one control treatment (without DB) for both varieties.
The number of open flowers was recorded for each treatment from the earliest application date to create the flowering curve and gather quality/productive information for each treatment.
Figure 1. Flowering curve (%) using HC at different application dates in cvs. Santina and Lapins.
The first flowers were recorded on 08.09.21 and 13.09.21 for Lapins and Santina, respectively. Observing the flowering dynamics, it is preliminarily evident that T1F3, with an application date of 14.06.21, was the treatment with the most advanced flowering in Santina, reaching 80% bloom on 17.09.21, five days earlier than T0. Meanwhile, in Lapins, T1F3 was the most advanced, reaching full bloom on 09.09.21, nine days earlier than the control treatment. However, in these treatments, it was noticed that the concentration of flowering, from the beginning of flowering to full bloom, was more dispersed compared to T0 and, in general, for many other treatments. It is well known that HC applications can cause some level of “disorder” in the early stages of flowering, which can be somewhat corrected by using homogenizing DB applications as a strategy to reduce such conditions. Clearly, this combination is aimed at obtaining harvests a few days earlier, which, consequently, lead to better synchrony in subsequent phenological stages.
The perfect recipe for DB application schemes or strategies does not exist because it must be tailored to each specific case, and the orchard must be well prepared from the post-harvest stage, taking necessary precautions for using these products.
Chilling Hours
Winter chilling is perhaps the most critical factor during the winter period. Once the post-harvest stage is complete, it is essential to focus on winter chilling, as it is decisive for achieving proper plant dormancy. Abscisic acid (ABA) is related to the accumulation of chilling, as it helps induce bud dormancy (para-dormancy) by inhibiting growth. It has an antagonistic relationship with gibberellic acid (GA), the latter being a promoter of growth (Fig. 2).
Fig. 2. Changes in physiological metabolic activities, including those affecting plant hormones in buds during dormancy (Kitamura, 2017).
As winter progresses in deep dormancy, known as endo-dormancy, we observe that as ABA decreases, GA increases, approaching the final stages of eco-dormancy. There is also an increase in auxin levels, indicating a recovery of metabolic capacity. CNH inhibits the enzyme catalase, which is responsible for breaking down hydrogen peroxide (H2O2) into water and oxygen, detoxifying it through a series of complex reactions in the pentose phosphate pathway, thus increasing metabolism and bud breaking. Indeed, there is synergy between endogenous metabolic processes and exogenous conditions (ambient conditions) that come together at the right time to implement these strategies.
There are also interesting productivity and quality traits that can be differentiated in each treatment (Table 1). For example, in terms of production, Santina showed a higher productivity level in T1F3, which had a significant difference compared to the last HC application (T1F6) in cv. Lapins. In both Santina and Lapins, T1F3 had the best quality parameters, considering the orchard’s load. Meanwhile, Santina in T1F1 showed lower productivity than the control treatment, indicating that early HC application may not be the most favorable for this variety.
Table 1. Productivity and quality indices for HC use at different application dates in cvs. Santina and Lapins.
The use of DBs is of vital importance for cherry production in Chile. It allows for staggered harvesting when there are extensive areas of cultivation, enabling the differentiation of early fruit in the market.
The accumulation of winter chilling, measured in chilling hours (Horas Frio in Spanish-HF) at a base temperature of 7.2 °C, is lower than the average in most of the cherry-growing region. The HF was even lower in the last season (2022/23). This may affect the timing of DB applications since at least 70% of the HF requirement for each variety should be fulfilled, considering the subsequent environmental conditions after the applications. A spring with low temperatures is forecasted, which is challenging to determine precisely. However, considering these probabilities, it is essential to weigh all historical information about the orchard, environmental patterns, among other factors.
*Avium team: Emilio Martínez, Agricultural Engineer; Nicolás Martínez, Agricultural Technician, Computer Engineer; Alex Vergara, Agricultural Engineer.
