The current cherry season has been marked by climatic imbalances in terms of the accumulation of cold hours, rainfall and heat accumulation towards the beginning of spring. In addition to the above, it is necessary not to forget how the plants are suffering from the effects of the previous summer in terms of temperature increases, incidence of spider mite attacks and a slow entry into dormancy.
One of the phenomena that has caused the most noise is the death of buds, colloquially known as “candied peanuts” due to their physical similarity to this product. The dead buds had this striking visual appearance and were left behind with the advance of phenology.
When looking inside these buds, in most cases their primordia were damaged, which in certain situations caused significant losses in flowering potential and a subsequent effect on fruit set.
It should be noted that based on permanent monitoring of fertility and bud quality analysis during winter, no such damage was evident, and it was expressed automatically and suddenly once the plant entered the swollen bud phenological stage.
This phenomenon is thought to be multifactorial in nature and it is important to provide a summary of the most important factors that could be influencing this phenomenon.
Although these factors are present in the vast majority of damage cases, their ranking will depend on each particular case. It should be noted that the order of the factors described does not respond to a ranking; the position of each of them will depend on the characteristics of each particular orchard.
This analysis is based on the recognition of different orchards and sectors, mainly in the earlier-warmer areas and valleys of the O'Higgins and Maule regions of Chile. In the central middle valley, in colder areas, the magnitude of the damage presented in the other sectors has not been evidenced and, so far, it is thought that it will not be of such incidence and severity.
1. Post-harvest stage.
1.1 It is recognized that in those orchards where post-harvest of trees was not ideal, there may be a higher incidence of damage. In addition, there are cases where significant periods of water stress were experienced, not to mention the challenges associated with managing abiotic stress during the period of floral differentiation.
1.2 During the late summer, central Chile was affected by an increase in temperature and a decrease in relative humidity, which caused a rapid and aggressive appearance of spider mites towards the end of February. This phenomenon caused the loss of photosynthetic capacity of the leaves, in addition to a gradual and rapid defoliation in many orchards. These events probably had a negative impact on the final stage of the floral differentiation process and the quality of the bud in its final stage of formation.
2.- Recess entry.
2.1 During the month of May, average temperatures close to 20 °C or higher were recorded, with higher maximum and minimum temperatures compared to 2022, when a more effective entry into the dormancy stage occurred. In many cases, the "trigger" effect usually associated with minimum temperatures, frost and a decrease in maximum temperatures to stimulate leaf fall was not observed. This could have caused a feeling of "disorder" in the plants.
2.2 Orchards where the entry into recess was slow, uneven and in those orchards where leaf persistence is recognized until a very late date, there is definitely a greater severity of damage.
On the other hand, in situations where strategies were developed based on cultural management to accelerate leaf fall and obtain a @50% of leaf fall by May 1, it is thought that these orchards naturally entered dormancy better, but at the same time had the possibility of better storing their reserves in fruit centers.
Regarding the previous point, those orchards that go through a normal process in terms of leaf fall and entering a recess have a better condition of accumulation of reserves in their fruit centers, not necessarily because this process accelerates the creation of reserves, but rather it is related to a natural signal of recess at the right time (end of April, first week of May) that will slow down a possible consumption of its own reserves to supply the need of the plant in a more active state, since the carbohydrate balance (creation and expenditure of carbohydrates) is negative.
3.- Dormancy breaker strategy.
There are a world of cases at this point, but what is most repeated is that in early areas, where applications were made very early during the first half of July, and especially those using a “tandem” system, including a homogenizer, there is more damage. This does not mean that the responsibility for the damage lies with the dormancy-breaking products, but rather it is a technical responsibility to be able to combine climatic and physiological factors to make correct decisions regarding these treatments, considering that this has become a new art.
3.1 Phenological states earlier than normal also have a certain relationship with damage. This means that orchards or varieties with very early flowering showed more damage in percentage terms than those with normal phenological dates.
Considering this, the effect of dormancy breakers (including hydrogenated cyanamide) on damage is related to the flowering date, not necessarily by causing any direct poisoning from the use of the product, unless it has been applied in overdose.
3.2 In this sense, the varieties with the greatest need for cold could apparently show more severity to the problem by concentrating the analysis in early areas with low cold accumulation this season.
4.- Climatic Events
4.1 Areas where the accumulation of cold units was at the limit and below thresholds, present more damage, but this is at the same time associated with poor thermal accumulation from the phenological state of red tips onwards.
4.2 It is not entirely correct to speak exclusively of a lack of cold to explain this phenomenon, if it were for this reason it would affect all fruiting centres in the same way. It is not yet understood what the pattern of damage is, nor how the branch or the spur discriminates the death of buds.
4.3 At the end of June, days of low thermal oscillation were observed, which had a sudden change to a high oscillation above what was observed in the previous season, accentuated in early areas, this followed by conditions of higher average relative humidity during the rest of the month of July, which could have facilitated the entry of free water to buds and with it the establishment of pathogens that would damage flower buds.
4.4 A preponderant factor in these anomalies is the “quality” of the accumulated cold.
4.5 High rainfall and flooding with saturated soils was a very present situation this season, where the operation was complicated to comply with phytosanitary protocols, but it also affected the normality of the plants in terms of energy expenditure and sprouting problems.
4.6 All these factors affect phenology, delaying its normality and making it impossible to rationally manage both irrigation and nutritional programs.
5.- Other considerations.
5.1 Cultural management such as stronger pruning and branch trimming apparently increases the severity of damage.
5.2 The incentive for greater vigor may be causing even more imbalance, a situation that will only begin to become apparent once the fruits are defined onwards, given that with less load the vegetative bud of the shoots has less competition, with the risk of developing the shoot and losing the fruit center.
In summary, there is no single factor that fully explains the incidence of this phenomenon. Among the main factors that have been related to its appearance are post-harvest management, climate, entry into dormancy, dormancy-breaking strategy and other cultural factors. The above underlines the importance of maintaining a comprehensive approach to address and mitigate this problem during future seasons.
Although this phenomenon conditioned the flowering potential in different situations, this was not the only anomaly, since the bad winter, accompanied by a bad spring in agroclimatic terms, has been a low blow mainly towards early areas, where, preliminarily, the unevenness in phenology and temperatures have not been optimal for the pollination and fertilization processes, affecting fruit set, which is still a fact under construction.
