The El Niño phenomenon had already announced that this spring would be unstable, and unfortunately, the forecast has been fulfilled to the letter. An example of this is the rainfall that will reach the central part of the country starting on October 28 and that will continue until the morning of Sunday 29.
According to the Meteorological Office of Chile, the rains will mainly affect the regions of O'Higgins, Maule and Biobío; although it will also rain in the Metropolitan region and Valparaíso. This event will be accompanied by temperatures that will not exceed 18ºC and will leave between 10-20 mm of rain.
The news comes literally like a bucket of cold water, considering the damage that rain can cause in orchards with advanced phenology. It should be noted that rain and even conditions of high relative humidity in fruit close to its ripening state, together with high temperatures, cause the internal pressure of the fruit to increase, which can cause microfractures that are the starting point of future cracks and that can subsequently lead to rot.
But why does this phenomenon occur? Well, the rain that is on the fruits enters the interior of the fruit due to the osmotic pressure differential, which at that time has a high content of sugars and other solutes.
Splitting or Cracking
Without a doubt, the terms “cracking” are common guests in cherry production; this condition in cherry trees is one of the main causes of discards when packing fruit for export.
This phenomenon has been studied by different authors (Cristensen, 1996, 1998; Ellena, 2001; Lugli and Lugli, 1998; Sansavini and Lugli 1997; Rombolá et al, 2005), who have determined that the main cause of cracking is the absorption of water through the epidermis of the fruit. This would cause the destruction of the outermost epidermal structures of the fruit. Additionally, absorption through the roots could cause fruit to split when rain occurs after long periods of drought (Godini, 1997).
According to the Inia article, Preventing cracking in sweet cherries, "The strategic alternatives currently available to counteract fruit cracking are basically covering the orchard with plastic nets (roofs) from about 10-15 days before harvest (high cost) and preventive foliar treatments based on calcium, foliar fertilizers and phytohormones or directly at the time of rain."
Handling rain
There are a number of management measures aimed at minimising the incidence of rain-related cracking in cherries:
-Hydrophobic protective products: These are protective hydrophobic waxy films based on natural phospholipids or fatty acids that prevent the absorption of water, preventing the fruit from splitting.
In our country there are three proven alternatives, which have managed to reduce the incidence and severity of cracking due to rain. It should be applied at the beginning of the straw color/beginning of the fruit appearance, considering that it should be done after the application of gibberellic acid.
It is extremely important to achieve perfect coverage of the fruit, since its effectiveness will depend on the physical protection of the fruit; it is necessary to carry out successive and well-controlled applications to achieve the objective, ensuring that the products are applied to the fruit in a homogeneous manner. Therefore, tests must be carried out in the target areas, pedicellar cavity and stylar zone, which is where the risk must be reduced, since prolonged exposure to water in these sectors ends in a crack.
-Pre-rain “saturation” irrigation: It consists of watering before rainfall in order to reduce the sudden absorption of water by the roots; in this way, it is possible to avoid the abrupt increase in the volume of the fruit, preventing cracking.
How to do it? You should start doing short waterings (2-3 hours), about 48 hours before
rain, in order to reach a state of soil saturation in the first 20-30 centimeters of depth.
This strategy should be repeated as many times as necessary in case of possible rainfall. It is necessary to consider that if this strategy is put into practice very close to rain, 12 hours or less in advance, it is advisable to continue watering while it rains. This is a very important strategy to prevent damage to orchards with plastic covers.
-Ca chloride (CaCl2): It has been determined that foliar application of calcium could reinforce the structure of cell walls, giving greater mechanical resistance to the tissues. Foliar applications of salts such as CaCl2 (and other salts such as K chloride, Mg chloride) allow the osmotic pressure between the inside of the fruit and the environment to be balanced, limiting the absorption of water by the fruit.
Constant and successive applications must be made before and during the rain episode, considering intervals of no more than 3 hours, in order to achieve the expected objective. Applications must be made at concentrations of 0.5% (500 g./100 L.) if the rainfall is less than 1 hour; if it is greater,
A concentration of 1% CaCl2 should be used, that is, 1 kg of Ca Chloride / 100 L of water.
Constant and successive applications before and during rainfall at use concentrations of 0-5%-1% have been favourable when proper operation has been maintained. The operation is complicated because it requires a high level of machinery, since it should be applied at maximum intervals of two hours in the same place while it is raining, in order to avoid the washing effect of the precipitation.
–Removing water from the canopy after rain: Removing water from the canopy of plants once the rain has finished, mainly from the pedicellar area of the fruits, is essential; this task can be carried out using helicopters or misting machines.
In the case of turbo-foggers, which are originally used to perform different applications in orchards, to dry the trees they must be unloaded, in order to generate wind flows that allow water to be removed. They must be used at full power, never completely empty, but with a little water so that the machines do not work dry. The first pass must be quick and a second pass must be considered in order to be able to remove all the water from the plants; a pass can also be made with two machines in parallel in adjacent rows, which makes the wind flows overlap to have greater effectiveness and remove water from the foliage and fruit. Ideally, blowers should be used, since their way of applying air is much more efficient.
With the same idea of generating wind, helicopters must fly over the plants; the route and height of the helicopter must be designed and established based on its size and power. It is important that at the time of the flight the soil of the orchard is somewhat humid, in order to avoid raising dust that can be harmful to the fruit and the execution of the work.
The use of helicopters is expensive, but it has proven effective in removing water from trees, preventing splits, especially those that are located in the pedicellar area known as the crescent.
Additionally, frost control propellers can also be used as complementary methods, as they produce wind that allows the water on the fruit to drain off and ultimately cause damage.
It should be considered a point of utmost importance that, in the event of rainfall, the orchards have received the proper application of fungicides, always keeping in mind the tolerances, considering the little time left for the harvest.
Another important point is that sensitivity to rain occurs from the straw-colored state/start of paintingBelow we share an image that makes it easier to identify this state.
Last season, at the beginning of November, 8 mm of rainfall caused damage to the fruit in certain sectors of the main cherry-producing regions (Maule and O'Higgins). This time it will rain twice as much, so it is necessary to carry out very efficiently all the strategies that allow minimizing the incidence of cracking due to rain.
Below we share a summary of what cherry producers affected by the rains did in the 2022-23 season.
