Spring rains? How to minimize the incidence of cracks in cherry fruits

Smartcherry

Management, Climate change, Agronomic Management, Climate

Spring rains? How to minimize the incidence of cracks in cherry fruits

April 1, 2024

Unlike years ago, the arrival of spring is no longer a certainty that the rain will fade away;

On the contrary, uncertainty seems to be the norm now, with each season bringing anticipation of different possible scenarios.

This anticipation, however, is absolutely necessary in the world of agriculture, where unexpected rain or a heatwave can completely change the productive outcome of a season. Rain and high humidity conditions, particularly in fruit nearing maturity, along with high temperatures, can increase the internal pressure of the fruits, leading to microfractures that are the starting point of future cracking and subsequent rot.

But why does this phenomenon occur? Well, rain that falls on the fruits enters them due to osmotic pressure differentials and at that moment, the fruits have high sugar and other solute contents.

Cracking

Undoubtedly, cracking is an unwelcome guest in cherry production; this condition in cherry trees is one of the main reasons for discarding 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 fruit’s epidermis. This would lead to the destruction of the fruit’s outermost epidermal structures. Additionally, root absorption could cause fruit cracking when rains occur after long periods of drought (Godini, 1997).

As the article by INIA, “Prevention of cracking in sweet cherries” points out, “the currently available strategic alternatives to counteract fruit cracking are basically covering the orchard with plastic meshes (roofs) about 10-15 days before harvest (high cost) and preventive foliar treatments based on calcium, foliar fertilizers, and phyto-regulators or directly at the time of rain.”

Management against rains

There are several management strategies aimed at minimizing cracking incidence due to rains in cherries:

Hydrophobic protective products: These are hydrophobic wax films based on natural phospholipids or fatty acids that prevent water absorption, thus preventing fruit cracking.

In our country, three proven alternatives have managed to reduce the incidence and severity of cracking due to rains. Their application should be carried out at the onset of the straw color/fruit paint stage, considering that it should be done after the application of gibberellic acid.

It is of utmost importance to achieve perfect coverage of the fruits, as their effectiveness depends on the physical protection of the fruits; successive and well-controlled applications are necessary to achieve the objective, ensuring that the products are applied to the fruit homogeneously. Therefore, tests should be carried out in the target areas, pedicel cavity, and stylar area, where the risk should be reduced, as prolonged exposure to water in these sectors results in cracking.

Pre-rain “saturation” irrigation: Consists of irrigating before precipitation to decrease the sudden absorption of water by the roots; thus, it is possible to avoid the abrupt increase in fruit volume, preventing cracking.

How to do it? Short irrigation (2-3 hours) should be started about 48 hours before the rain, aiming to achieve soil saturation in the first 20-30 centimeters of depth.

This strategy should be repeated as necessary before possible precipitation. It is necessary to consider that if this strategy is implemented shortly before the rain, with 12 hours or less anticipation, it is advisable to continue watering while it is raining. It is a very important strategy to prevent damage in orchards with plastic covers.

Calcium Chloride (CaCl2): It has been determined that foliar calcium application could reinforce the structure of cell walls, providing greater mechanical resistance to tissues. Foliar salt applications such as CaCl2 (and other salts such as KCl, MgCl2) allow balancing the osmotic pressure between the fruit’s interior and the environment, limiting fruit water absorption.

Constant and successive applications should be carried out before and during the rain episode, considering intervals no longer than 3 hours, in order to achieve the expected objective. Applications should be made at concentrations of 0.5% (500 g/100 L) if the rain lasts less than 1 hour; if it lasts longer, a concentration of 1% CaCl2 should be used, meaning 1 kg of CaCl2 per 100 L of water.

Constant and successive applications before and during rain at concentrations of 0.5%-1% have been favorable when proper operation could be maintained. Operation is complicated due to high machinery demand since it should be applied with maximum intervals of two hours per same spot while raining to mitigate the washing effect of rainfall.

Post-rain canopy water removal: Removing water from the canopy of the plants once the rain has ended, mainly from the fruit’s pedicel area, is crucial; this task can be accomplished using helicopters or misting machines.

In the case of misting machines, which are originally used to carry out different applications in orchards, to dry the trees, they must be unloaded, to generate airflows that allow water removal. They should be used at full power, never completely empty, but with a little water so that the machines do not work dry. The first pass should be quick, and a second pass should be evaluated to remove all the water from the plants; a pass with two parallel equipment in adjacent rows can also be done, which makes the wind flows overlap for better effectiveness and removes water from the foliage and fruit. Ideally, blowers should be used since their method of applying air is much more efficient.

Following the concept of wind generation, helicopters must fly over the plants; the route and altitude of the helicopter must be designed and established based on its size and power. It is important that the orchard floor is somewhat moist at the time of flight to avoid raising dust that can be harmful to the fruit and the execution of the task.

The use of helicopters is costly, but it has shown effectiveness in removing water from trees, preventing cracking, especially those located in the pedicel area known as the “half-moon.”

Additionally, frost control propellers can also be used as complementary methods, as they produce wind that allows water on the fruit to drain off, thus preventing damage.

It is crucial to consider that, in the event of precipitation, orchards have received the proper application of fungicides, always keeping in mind tolerances, considering the limited time remaining until harvest.

Another important point is that sensitivity to rains occurs from the onset of the straw color/fruit paint stage. Below is an image that allows for easier identification of said stage.