Carlos J. Tapia T. Agricultural Engineer M. Sc. Specialist in cherry production. Avium Technical Director and Co-founder of SmartCherry.

The main objective in this transition stage is to be able to have the beginning of physiological dormancy around May 1.

Physiological dormancy can be recognized when the tree reaches at least 50% of leaf fall, always considering that yellow leaf is considered leaf fall. With this, an acclimatized and “hardened” plant is ensured to withstand low temperatures and frost events in the dormant period, and also, for its part, the accumulation of cold hours is maximized and thus begin to count them early in the season. .

What must be taken into account so that the plants can acclimatize quickly and enter a period of dormancy in an optimal way? Several aspects that we will know next.

Postharvest nutrition:

Regarding the management of postharvest nutrition and fertilization, the months of January and February are those that are considered the most important in terms of orchard recovery. This means that, as well as heat stress prevention, soil and foliar fertilization based on results, are vital to ensure reserves and start a new season after the dormant stage.

The month of March is already recognized as a month of transition at the beginning of the winter dormancy stage, for which it is important to generate a signal to the plant from the nutritional point of view and not continue fertilizing beyond March 10, to do not over-stimulate the plant or maintain a vegetative state until late in the season. This considers both soil fertilization and postharvest foliar programs.

Irrigation programming and management:

The atmospheric demand and the water consumption of the plant are decreasing towards the end of February and the beginning of March. The demand is expressed in evaporation and not in ambient temperature. This is important to understand, because although there are high temperatures at this time, they last only a few hours in the day and are not comparable to the same maximum temperatures in midsummer.

In turn, the nights and mornings have much more marked low temperatures and with a high presence of humidity than in the months of January and February. The foregoing is the basis for the decrease in the frequency of irrigation towards the month of March. It is very important to use tools that help to make objective decisions for this: Test pits, humidity sensors, tensiometers, etc.

The change in the frequency of irrigation (not the time) in normal conditions should decrease between 30% and 50% of what is established in summer by the third week of March.

In general, the risks must be suspended towards the end of March. With this, a signal is generated to the plant and begins the process of wood lignification and fruit centers so that the plant can better withstand the low winter temperatures. However, in soil conditions with less water retention, as is the case with sandy soils and also with the presence of stones, the cessation of the irrigation season must be postponed until April 10.

In special situations, it could be irrigated again at the beginning of autumn and the beginning of very dry winter, but never before recognizing physiological dormancy, represented as at least 50% of fallen leaves (yellow leaves are considered fallen leaves).

Use of Molybdenum (Mo) as a complement to the acclimatization of plants:

Much is said about the action of Mo as an enhancer of leaf fall or as a causal agent of the physiological entry of plants. However, this component acts through the nutritional pathway, moderating and enhancing the action of some nutrients, such as distributing the different nitrogenous forms that are in plants, in favor of reserves, and the action of some phytohormones such as ethylene and acid. abscisic, the latter being the cause of triggering leaf fall naturally in autumn.

Mo foliar applications during the month of March have shown to be effective in an acclimatization process, mainly of young plants; the foregoing, especially in colder areas to enhance the hardening and lignification of the plants, in order to improve the adaptation for the process of leaf fall and to be able to better withstand the low winter temperatures, favoring the condition of the plants from the phytosanitary point of view.

A plant adapted to the environment, often due to the use of foliar Mo, may have better options of being able to carry out the process of leaf drop in a natural and normal way to the extent that there are environmental signals that allow it. In this case a constant drop in ambient temperatures.

There are many commercial options of Mo formulated for foliar application on the market. The concentrations of use according to the manufacturer must always be respected.

Strategy to complement leaf fall:

The punctual consideration is that physiological dormancy should ideally be presented at the beginning of the month of May. The first cultural signal that must be given to the plant to begin its entry into dormancy is to stop watering towards the end of March; that complemented with the cessation of soil and foliar fertilization towards the end of February. After this, the state of yellowness and/or leaf fall should be evaluated (yellow leaf = fallen leaf).

This evaluation analysis should be done around April 15 to 20, since it is a reasonable time for the plants to present changes based on what was done as the primary strategy. If at that date there is no outline of leaf fall, a chemical strategy must be applied to ensure its fall.

Tests have been carried out that allow a rapid response to throwing away leaves if necessary, the most effective being the least “natural”, which is through the “intoxication” of tissues.

In this case, it is recognized that the sulfate ion (SO 4 ), present in some nutrients, generates intoxication of green tissues when used in high concentrations, so it is the way to stop the work of the leaves and generate abscission. However, the mixture with urea has enhanced the decomposition effect, generating a rapid fall.

Hence the mixture between a “de” Sulfate (Zn Sulfate the most used) plus Urea, as a complement to throwing away leaves in a last resort terminal strategy. The use concentrations of both formulated products are between 1% and 2% always mixed. Up to two applications could be made at 7-10 day intervals if necessary.

Coverage should be used according to the crown volume and always favoring reaching the last shoot in height.