The use of dormancy breakers (RD) in our crops will always be an alternative that must be taken with rigor and that will go hand in hand with a technical/commercial objective, and also determined by the type of variety being treated.
This is why it is always necessary to take into account that this type of strategy goes against the normal nature and phenology of the species and that in many cases it could even subject the plants to unnecessary stress.
Based on the Chilean experience, minimum requirements should be met for the application of RD, hoping that its result will be technically correct.
1. Garden health: An orchard with phytosanitary problems of various kinds is an orchard that is weaker, and any stress at any stage of its phenology could cause more problems to the detriment of its future condition.
2. Cold accumulation: Each variety must have accumulated at least 70% of its chilling requirements before dormancy breakers can be applied. It should not be “awakened” or dormancy broken if this requirement has not been met, otherwise an unnecessary imbalance in its phenology will occur.
2.1 Cold requirement:
| Cherry variety | Cold hours < -7°C |
| Royal Dawn | 400 – 500 |
| Santina | 700 – 800 |
| Stella | 600 – 700 |
| Bing | 700 – 800 |
| Lapins | 500 – 600 |
| Kordia | 1,000 – 1,200 |
| Sweetheart | 700 – 800 |
| Regina | 800 – 1000 |
*Source: El Campo-El Mercurio Magazine Carlos Tapia Agricultural Engineer, M.Sc., specialist in cherry production and technical director of Avium SpA.
3. Date of application: The use of a breaker will be determined by the temperature conditions of each year, and within certain limits. Just because, for example, a Lapins reached its cold requirement on June 20th does not mean that the RD should be applied on that date, since for the treatment to be as effective as expected, it must be directly related to the ambient temperature after application. It is estimated that the base ambient temperature to accelerate physiological processes is above 15°C. Also consider that the state of the floral structures after application is more susceptible to cold damage, so frost events after the application of RD are triggers for an eventual loss of productive potential.
4. Use of concentration: It is important to note that dormancy breakers are not worked in doses per hectare, but in concentration or percentage: for example, 2 liters in 100 L (2%), 3 L in 100 L (3%), etc.
The effect of RD is directly related to the increase in concentration and it has been proven in Chile that concentrations greater than 3% do not generate a greater gain in the effect. The dose per hectare will be determined by the orchard's coverage needs.
5. Coverage: In past research, it was determined that the optimal coverage of dormancy breakers to achieve the objective and minimize the risk of poisoning is 75% of the canopy volume (VHA) measured on the date of application.
The VHA (Tree Row Volume – TRV) measurement aims to recognize the actual canopy volume expressed in L/ha to objectify foliar applications.
This information is of vital importance in order to program the spraying based on the actual volume required.
The VHA responds to the following formula:
Cup Width: Calculate an average of the bottom and top width (measured from the first branches) projected in the row.
High Cup cash: Calculate the height of the crown from the first fruit branches to the apex of the plant, without considering the trunk.
936: Conversion factor to convert to L/ha.
Distance between rows: measured in meters from the center of each trunk.
Therefore, for example, if the recommended concentration were 2% of hydrogenated cyanamide and the measured canopy volume is equivalent to 1,000 L/ha, 75% coverage is achieved with 750 L/ha, where 15 L/ha of the product would be required, this being the dose.
If instead it were applied with a 100 % coverage, 1,000 L/ha would be used, equivalent to a dose of 20 L/ha of product, without having any positive effect on the application objective, but causing overexposure of the tissues to the treatment and often assuming an unnecessary risk in terms of potential poisoning.
6. Calibration of application equipment: It is vital that the application equipment must be properly and correctly calibrated and checked before applying dormancy breakers, in order to achieve the objective proposed with this type of treatment. There are companies specialized in the maintenance and calibration of this equipment, which guarantee its correct use for the rest of the season's applications.
