Preparation for the dormant period

Preparation for the dormant period

Entry into dormancy and leaf fall cherries
and strategies for leaf fall
Entry into dormancy and leaf fall cherries
  • Just like when a person gets ready to go to sleep and performs a routine before rest, cherry orchards must also meet certain conditions for proper winter dormancy. The difference is that they cannot do it on their own, therefore completing the foliar and soil nutritional programs, and suspending irrigation in time, is essential for proper entry into dormancy.

As the days go by and the scene begins to change in the cherry orchards, where the green of the post-harvest is replaced by the yellow leaves of autumn, many of them already on the ground or about to fall, we face a new stage within the phenological development cycle of the cherry tree: dormancy.

However, this winter lethargy of the plants will directly depend on what happens in the post-harvest orchard, on the agronomic management and the signals that are given to the plants; the concept of postharvest does not refer, particularly, to the moment after the harvest has finished, but to the postharvest of the trees, of a physiological change of the plants. The physiological postharvest responds to some ecological stimulus and is more or less between 80 to 150 days after full flower (DDPF).

It is extremely important to worry about and take care of the postharvest stage, mainly its first stage and understand that it has a beginning and an end, taking advantage of it as a stage prior to dormancy, where we have to deliver some information to the plant in terms of signals so that it understands that it is going to sleep.

During the transition between post-harvest and entry into dormancy, all orchard recovery programs must be completed, from a nutritional, soil and root point of view. In addition, all foliar corrections must be completed in response to the analyzes that were carried out at the beginning of the postharvest stage.

Time to sleep

Dormancy is understood as the winter lethargy of plants, in which the accumulation of cold hours occurs, which is directly related to the use of the reserves that the trees have to start the next season, in favor of the productive objective of achieve its potential in terms of quantity, quality and condition of fruit.

The beginning of this stage can be defined in several ways, which is why it is essential to analyze it. Physiologically, the tree begins its state of dormancy when it manages to reach 50% of its fallen leaves in autumn, and we have to try to make it coincide with November 1, because that is when the official start of the count of cold hours, which will extend in the following months.

Irrigation programming and management towards the end of the season

As we mentioned, one of the signals that we must give to the plants in post-harvest for a correct entry into dormancy is irrigation; It must always be taken into consideration, but especially in this phase, that efficient irrigation its not related to the amount of water supplied based on consumption, but to a whole concept that is its distribution; special attention must be paid not only to the amount of water to be replaced in terms of evapotranspirative demand, but also to the decrease in volumetric terms of soil, of the roots of the different rootstocks.

As a general recommendation for programming and managing irrigation towards the end of the season, it should end in the month of September, in order to generate a signal to the plant and begin the process of lignification of wood and fruit centers, thereby An acclimatized and strong plant is ensured, which will allow it to better withstand low winter temperatures. For soil conditions with lower water retention, such as sandy soils and also with the presence of stones.

Aspects to consider

  • Demand is expressed in evapotranspiration and not in environmental temperature, which is why high temperatures in autumn are not comparable to those of the summer period, as they only last a couple of hours.
  • Starting in September, the nights and mornings are colder and wetter, which should be considered for reducing the frequency of irrigation.

Can we water it again? Yes, but in special situations, for example at the beginning of autumn and the beginning of very dry winter, but never recognizing physiological dormancy, represented as at least 50% fallen leaf (yellow leaf = fallen leaf).

Ecological signs

The first important signal that declares dormancy is the change of season, which marks a very important moment in the beginning of the lignification and pre-dormancy processes and that in physiology is defined as “cold tolerance”.

When there is a change in the photoperiod, the annual materials that grow already have lignified basal sections, and it is possible to notice wood, a clear sign of the shortening of the photoperiod that affects the beginning of flower induction. With the shortening of the photoperiod, the plant enters a process of accumulating reserves, changing sap flow and going to “get ready to sleep.”

Another ecological event that enhances and ensures dormancy is the first autumn frost, and that concept in the physiology of fruit plants is called “freezing resistance”, that is, there is already development of secondary growth wood; This is a trigger for the plant to shed its leaves, enter a powerful autumn situation and voluntarily go to sleep.

What should we see in cherry plants before going dormant? Fruit centers with very well-formed darts, with very smooth bracts, still with the presence of leaves, since it must be considered that the buds are always axillary to leaves. Additionally, 50% of fallen leaves.

The concern that the plants enter the dormant period on this date lies, mainly, in ensuring that all their structures are highly acclimatized and lignified to withstand the winter and that, thus, there are no imbalances from the point of view of loss of potential. and not phytosanitary either. On the other hand, because these plant processes require a change of switch at that time, since if it enters a more permanent vegetative cycle, the balance or the dynamics of reserve recovery is negative; What the plant can produce carbohydrates on that date is much lower than the carbohydrate consumption rate, therefore the differential is coming from the same reserves that were obtained post-harvest.

If the plants enter dormancy by November 1, this will allow them to take advantage of the winter dormancy, considering the month of October as the most important in terms of accumulation of cold hours. However, it must be kept in mind that good dormancy is not only determined by the accumulation of cold, but also by how short the photoperiod is, that is, how much light you have.

But what to do if we don’t have an answer with these strategies? If by October 20 our orchards do not have 10-20% yellow leaves, decisions must be made on how to accelerate this process.

Strategies for leaf fall

Option 1: Natural Signal

A natural signal is the use of Ethylene as a promoter of Abscisic Acid which, in turn, promotes leaf fall. It should be applied early in the season, however, it should be considered that it will generate some delay in flowering, which may or may not be beneficial, depending on the characteristics of the variety, the area and the commercial objective.

On the other hand, it is necessary to keep in mind that a plant subjected to biotic or abiotic stress generates Ethylene, therefore it is an action that must have basic considerations; In orchards that are not in optimal phytosanitary conditions, make indiscriminate applications of Ethylene to promote acclimatization and leaf fall.

This is a technique that continues to be studied in order to refine it and adjust it to use correctly.

Option 2: Acclimatization

A few years ago Molybdenum appeared (from a nutritional point of view) as a good acclimatizer; in its nutritional nature, it is part of the nitrogen metabolic processes, which allows generating responses that decrease the rate of development in spring and acclimatization in autumn or entry into winter. The objective of Molybdenum is to harden wood and acclimatize and it will respond to a successive application program, three or four applications every 7 days, from mid or end of September onwards, so that in the second half of October it has a clear effect on the plants.

Option 3: Intoxication (Zn Sulfate 2% + Urea 2%)

It is a measure that should be considered as a last strategy and not in the first days, it is a very helpful option and a quick response to leaf fall. This is produced through poisoning through Sulfate, which will cause poisoning of the leaf, but will not throw it away. However, when mixed with 2% urea, the decomposition process of the leaf will be accelerated, which will ultimately cause it to fall.

If fertilization and irrigation have been completed, this third option has a very good effect, however, in very vigorous orchards the application could be repeated for optimal results.

In conclusion…

Problems with plant acclimatization for their entry into dormancy can lead to a series of negative consequences, including damage to primordia; studies show that most of the damage to primordia is not related to frost in certain phenological stages, such as swollen bud, for example, but to the acclimatization. This, in turn, generates loss of potential and can trigger a vicious circle of permanent phytosanitary problems.

The time of winter dormancy is near and our plants must have all the signals to acclimatize, prepare to withstand the low winter temperatures and enter a correct dormancy that allows them to accumulate the optimal number of cold hours, waiting for the blossom in order to have a new productive season.

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