- In recent years, April has had higher temperatures, similar to summer.
- The lack of cold hours in autumn means that plants do not begin their dormancy as they should.
Since the plant needs to prepare for proper lignification of its vegetative and reproductive structures after the end of summer, it is during the fall that its first period of dormancy begins. However, in recent years there have been warmer autumns that directly affect the viability of the shoots.
Once the post-harvest is over, the month of March and the first half of April become transition months, and from March onwards it is necessary to propose a more precise irrigation schedule than what was done in the summer. The frequency of irrigation must be reduced, and probably not watered at 100% evaporation, so that in operational terms irrigation is stopped in the last week of March, which will probably be the first cultural signal that will be given to the plant so that it can acclimatise and begin to drop leaves naturally.
If no signs of leaf fall are seen by April 15 or 20 (always considering that leaf fall is a yellow leaf), it is important to artificially promote leaf fall. The most common method used in Chile is poisoning, which involves applying a mixture of a sulphate, such as zinc sulphate, plus urea, both at 2%. This process of promoting leaf fall has several favorable factors. First, it forces the plant to enter physiological dormancy and that this physiological dormancy is always close to May 1, since theoretically it is the date on which plants could begin their record of cold accumulation.
“Physiological dormancy is related to the 50% of the fallen leaf, therefore, once the plant reaches this process, and is able to accumulate cold hours, the ideal is for it to occur from May 1st., which also leads to another important consequence; first, the plants by promoting leaf fall probably stopped consuming the reserves they had accumulated by the action of their vegetative metabolism and also the fruit centers are prepared, such as darts and bases of twigs, so that they spend a very good winter with everything that means protection of the buds, well-formed and well-closed bracts, so that they have less sensitivity to autumn and winter frosts, and many times that they are well covered so that they can withstand the application of dormancy breakers and even the application of coppers that seek to prevent bacterial and fungal diseases..” said Carlos Tapia, Director of Avium.
Given this situation, it has recently been recognized that foliar applications of molybdenum (Mo) contribute to providing a more nutritional signal from the acclimatization point of view. Considering that Mo contributes to the action of an enzyme (protein) called nitrate reductase responsible for regulating nitrogen (N) metabolism within the plant. Nitrate reductase has Mo in its formation, therefore, the action of this foliar nutrient that is applied exogenously to plants contributes to generating greater activity and detrimentally affects N metabolism as a direct signal in physiological terms for acclimatization.
“Mo has been used in recent years mainly for acclimatization and hardening of the wood of new trees, however, it could be used in orchards with a lot of vigor and with a lot of vegetative activity in the season, this as a complement for when the water supply is modified at the end of March with the aim of acclimatizing the plant and achieving a more natural fall of leaves towards the beginning of May.". Tapia added.
Bibliographic references
- Carlos Tapia- Personal communication.
