The current cherry season has been marked by climatic mismatches regarding the accumulation of chill hours, rainfall, and thermal accumulation towards the beginning of spring. Additionally, it’s important not to overlook how plants carry over effects from the previous summer in terms of thermal increases, incidence of spider mite attacks, and a slow entry into dormancy.

One of the phenomena that has caused considerable concern, at least in the counter-season of the southern hemisphere, is bud death. The dead buds had a visually striking appearance and were left behind as phenology progressed.

Upon examining the interior of these buds, in most cases, their primordia were found damaged. This resulted, in certain situations, in significant decreases in flowering potential and subsequent effects on fruit set.

It’s worth noting that based on continuous monitoring of fertility and quality analysis of buds during winter, such damage was not evident, and it manifested abruptly once the plant entered the swollen bud phenological stage.

It is believed that this phenomenon is multifactorial in nature, and it is important to summarize the most significant factors that could be influencing it.

While these factors are present in the vast majority of damage cases, their ranking will depend on each particular case. It should be clarified that the order of the described factors does not represent a ranking; the position of each factor depends on the characteristics of each specific orchard.

This analysis is based on the recognition of different orchards and sectors, mainly from the earliest-warmest zones and valleys of the O’Higgins and Maule regions of Chile.

Post-harvest stage:

1.1 It is acknowledged that in orchards where post-harvest tree management was not ideal, there may be a higher incidence of damage. Additionally, there are cases where significant periods of water stress were experienced, not to mention the challenges associated with managing abiotic stress during the floral differentiation period.

1.2 During the end of summer, the central zone of Chile was affected by an increase in temperature and a decrease in relative humidity, leading to a rapid and aggressive appearance of spider mites towards the end of summer. This phenomenon caused a loss of leaf photosynthetic capacity, combined with gradual and rapid defoliation in many orchards. These events likely had a negative impact on the final stage of the floral differentiation process and the quality of the bud in its final formation stage.

Entry into dormancy:

2.1 During the month of May, in full autumn in the southern hemisphere, 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 dormant stage occurred. In many cases, the “trigger” effect usually associated with minimum temperatures, frosts, and a decrease in maximum temperatures to stimulate leaf fall was not observed. This could have caused a sense of “disorder” in the plants.

2.2 Orchards where entry into dormancy was slow, uneven, and where persistent leaf retention was recognized until very late dates, definitely showed greater severity of damage.

On the contrary, situations in which strategies were developed based on cultural management to accelerate leaf fall and achieve a 50% leaf fall by May 1st are believed to have naturally entered dormancy better, but at the same time had the possibility of better preserving their reserves in fruiting centers.

With respect to the previous point, orchards that undergo a normal process of leaf fall and entry into dormancy have a better condition of reserve accumulation in their fruiting centers, not necessarily because this process accelerates reserve creation, but because it is related to a natural signal of recess at the opportune moment (late April, first week of May) that will halt a possible consumption of their own reserves to meet the plant’s needs in a more active state, since the balance of carbohydrates (creation and expenditure of carbohydrates) is negative.

Dormancy breakers strategy:

In this point, there is a world of cases, but what is most repeated is that in early zones, where very advanced applications were made during the first half of July (midwinter), and especially those using the “tandem” system, including a homogenizer, there is more damage. This does not mean that dormancy-breaking products are responsible for the damage, but rather it is a technical responsibility to combine climatic and physiological factors to make appropriate decisions regarding these treatments, considering that this has become a new art.

3.1 Phenological states anticipated to normality also have a certain relationship with the damage. This means that orchards or varieties with very early flowering showed proportionally more damage than those whose phenological dates were in normal situations.

Considering this, the effect of dormancy breakers (including hydrogenated cyanamide) on the damage is related to the flowering date, not necessarily because they generate any direct intoxication due to the use of the product, unless applied in overdose.

3.2 In this sense, varieties with greater cold requirement apparently could show more severity to the problem by focusing on early zones with low cold accumulation this season.

Climatic Events:

4.1 Areas where the accumulation of chill units was at the limit and below thresholds show more damage, but at the same time, this is associated with poor thermal accumulation from the phenological stage of red tips onwards.

4.2 It is not entirely correct to exclusively talk about lack of cold to explain this phenomenon, if it were for this reason, it would affect all fruiting centers in the same way. It is not yet understood what the damage pattern is, or how the branch or bud 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 seen in the previous season, accentuated in early zones, followed by conditions of higher average relative humidity during the rest of July, which could have facilitated the entry of free water into buds and thus the establishment of pathogens that would damage floral buds.

4.4 A predominant factor in these anomalies is the “quality” of accumulated cold.

4.5 High rainfall and floods with saturated soils were very present this season, where operation became complicated to comply with phytosanitary protocols, but also affected the normality of plants in terms of energy expenditure and budding problems.

4.6 All these factors affect phenology, delaying its normality and without being able to rationally manage both irrigation and nutritional programs.

Other considerations:

5.1 Cultural practices such as stronger pruning in thinning and branch trimming apparently increase the severity of damage.

5.2 The incentive for greater vigor may be causing even more imbalance, a situation that will only begin to be visualized from the time the fruits are defined onwards, since with less load, the vegetative bud of the darts has less competition, with the risk of developing the sprout and losing the fruiting center.

In summary, there is no single factor that completely explains the incidence of this phenomenon. Among the main factors related to its occurrence are post-harvest management, climate, entry into dormancy, dormancy-breaker strategy, and other cultural factors. This underscores the importance of maintaining a comprehensive approach to address and mitigate this problem in future seasons.

While this phenomenon conditioned the flowering potential in different situations, it was not the only anomaly, as the poor winter, accompanied by a bad spring in agroclimatic terms, has been a setback mainly for early zones, where, preliminarily, the non-uniformity in phenology and temperatures have not been optimal for pollination and fertilization processes, affecting fruit set, which is still data under construction.