As soon as the cherry harvest ends, a new stage begins, which is known as post-harvest. It is at this point that producers must pay special attention, since the orchards need care and management that allows them to recover after a hard season of work.
One of the tools that has been widely used and studied in Chile is the application of sunblock. But how do these elements really work on cherry trees?
First, and from a physiological point of view, they help prevent premature closure of the stomata; pores invisible to the human eye, which are on the underside of the leaves and which allow, among other functions, gas exchange with the atmosphere, allowing cooling of the plant and the generation of sugars. This is especially relevant because these stomata are responsible for releasing water from the plant and capturing CO2, the raw material for sugars.
Factors to consider
Generally, this type of thermal-hydric stress prevention tools are used on weak, less vigorous rootstocks or in some less vigorous orchards. – It is important to note that vigour is measured by the recovery of annual growth, that is, if an annual growth of over 50-70 centimetres is recognised, it can be said that the garden is well-vigorated or balanced. Do not confuse large gardens with vigorous gardens, because there may be a giant garden that is very voluminous, but without vigour.
In addition to vigour as a determining factor in making this decision, it must also be considered that in seasons like this, with very hot areas or areas where there is a significant water deficit, sunscreen can be an aid in weighing up the weather scenario.
However, when using these tools, it is important to consider that the key to preventing problems associated with abiotic stress is the efficient use and programming of irrigation. This remains the most foolproof method to avoid problems associated with water and/or heat stress in plants, and all sunscreen or filter treatments come to accompany these basic management practices in the development of the crop.
The best option
In this regard, the specialist advisor in cherry production and founder of Avium, Carlos Tapia, explains that “we should not limit ourselves to the use of strategies to prevent this thermal and water stress, since they are only used when low-vigor rootstocks are used. In this context, what rootstocks could respond to this need, obviously the Gisela series, including Gisela 5, Gisela 6, Gisela 12; although Gisela 12 is the most vigorous of the series, in many areas its use could be justified. We should not forget the direct relatives of these Gisela, which are the versions of sour cherry. So, although we have and can recognize different vigor statuses of sour cherry, we do recognize that there are a large number of sour cherry orchards that respond to less vigor than more vigor.” On the other hand, it adds the MaxMa series, including MaxMa 14, MaxMa 60 and their direct “relatives”, some Mahaleb, Santa Lucia and Pontaleb.
What do the records of recent years say about sunscreen applications in Chile? The most extensive experience is the use of 95 percent kaolinites. “The use of these products ranges between 2.5 and 3 percent. And although there are some that have a lower label concentration, we believe that their use could also be effective and we have shown in recent years that orchards applied with this type of product maintain their leaves at a lower temperature throughout the day, at the different times that we have taken measurements, also adding to stomatal flow measurements where positive differences are always recognized after midday, showing greater stomatal conductance in treatments with sunblock,” adds the specialist.
Other alternatives
Recently, we have also become aware of colourless sunscreens, which are also interesting tools for pre-harvest applications.
According to the same studies carried out by Avium, some of them have presented interesting results in the prevention of direct damage to the fruit, such as dehydration of pedicels, sunstroke on fruits and even improving quality indicators in the post-harvest. And although the formulation is very different from conventional blockers, they can be an alternative for the post-harvest period.
Avium's Research and Development Department has carried out a series of tests on the use of sunscreens on cherry trees. About five or six seasons ago, they incorporated certain additives or ingredients into these kaolinite applications that would improve or support the use of kaolinite, using the biochemical method of controlling thermal and hydric stress. They carried out tests with extracts of algae of the Ascophyllum nodosum type, and even some amino acids.
“The results have been super consistent, the orchards with kaolinite alone lower the leaf temperature compared to the control. And when we add some additive to these kaolinites that allows for biochemical improvement, this stress prevention lowers the temperature even more or keeps the leaf temperature cooler, since the concept is not to lower the temperature, but to prevent its increase and premature stomatal closure. We have understood over time that not only Ascophyllum nodosum could do this job, but also products that have folcisteine in their composition or also the use of some amino acids that mainly in their composition could highlight proline, which is also directly linked to the prevention of thermal hydric stress,” explains Carlos Tapia.
The right moment
As for when to start applying sunscreens in orchards, ideally immediately after harvest and perhaps up to a week after harvest. Ideally, this strategy or these applications should be repeated every 25 to 30 days. That is, it can be done in the spring season, or late spring, and in the summer, do two applications.
With this schedule, it has been detected and studied that there is a better temperature of the sheet with respect to the witness and consistently, there is a better operation of carbon reserves in the darts measured in winter, which reserves? total nitrogen, total protein, amino acids, some amino acids and starch.
It should be considered that the month of January corresponds to the period of floral differentiation in the central zone, therefore, it is of great importance that during this period the plants are in the best conditions, so that this physiological process of flower bud formation occurs when the plant has a balance in terms of water, heat and metabolism.
