During this period, it is essential to provide the orchards with all the favorable conditions that allow them to carry out the greatest amount of photosynthesis possible, which will translate into an adequate accumulation of reserves for the following season.
When the vast majority of orchards in the central part of the country are reaching the end of the harvest and the later areas are beginning what will be a rather concentrated and brief fruit harvest, it is necessary to have full clarity of the relevance of the post-harvest, a period that begins immediately after the harvest and extends until the beginning of autumn.
It is during the post-harvest period that important processes occur in our orchards that will be of crucial importance for the following season. It is therefore necessary to address a series of threats typical of the summer season, which if not detected and controlled could affect normal productive development.
“From a physiological point of view, the induction of flower buds and the initial stages of bud development are occurring. In many cases, this occurs even before and during the harvest, we are talking about the months of November and December. Then, during January and February, comes the stage of differentiation of the floral organs. Both the induction and the floral differentiation are irreversible processes, but they will be negatively affected by several factors, one of them being the high temperatures and/or the water deficit that affects a large part of the country. Another important thing that can affect these processes is the failure in the supply of carbohydrates. I am talking mainly about a decrease in the photosynthetic capacity of the orchards and nutritional deficiencies such as: mainly Nitrogen, Potassium and Magnesium.” explained Eduardo Parra, Technical Manager of Zeroseven.
Another element that could also affect these processes is early defoliation or early senescence, mainly due to the thermal and water stress characteristic of this time of year and which coincides with the post-harvest period.
“The high temperatures of summer, the water deficit we are experiencing, added to the high radiation we have in the country, form an almost perfect triangle for stress that is very negative from the point of post-harvest for our orchards,” warned Eduardo Parra.
According to Zeroseven's Technical Manager, if we compare the Curicó area, for example, with the northern hemisphere at the same latitude, we have twice as much radiation as California.
“This high radiation is affecting the photosynthetic rate, and from a more physiological point of view it is causing a destruction of photosystem II and some photosynthetic enzymes; we have from this excess of radiation, a lower concentration of chlorophyll, all of this having repercussions on problems of low photosynthetic rate, there is also an impact on the endogenous metabolism of auxins, a lower concentration of amino acids important for the accumulation of reserves and an increase in the concentration of ammonium in our plants, explained Eduardo Parra, Technical Manager of Zeroseven.
There are also nutritional effects that can be detected with the naked eye.
“It is very common to find damage to the leaves during this period, which apparently seems to be a burn, especially common in orchards over Maximum 14, this is also a product of the high radiation that the plant suffers, also associated with a deficit in the concentration of Magnesium; orchards that are exposed to high light radiation have higher Magnesium requirements compared to orchards that grow in conditions of low light radiation”, Eduardo Parra evidenced.
It is vitally important to be able to detect and control the factors that can have a negative impact on orchards, especially considering that climate change is resulting in increasingly hot summers, more frequent heat waves and high solar radiation.
“We must take care to provide all the favorable conditions for the garden, which will allow them to carry out the greatest amount of photosynthesis possible, understanding that the result of this photosynthesis will be an adequate accumulation of reserves, mainly carbohydrates for the following season. During this post-harvest period, during the summer, all the photosynthesis that the garden does must translate into an adequate accumulation of reserves that are what will give us the start in the following spring,” explained Zeroseven's Technical Manager.
Fortunately, there are tools to reduce or minimize this water and heat stress. The use of sunscreens or sunblocks are an excellent alternative to minimize the effects of the adverse conditions that the summer season offers to orchards.
“Personally, I prefer kaolin, because it reflects light very well, which helps to lower the temperature of the plants; the application of this type of protector should be done immediately after the harvest and the idea is to repeat it every 25-30 days so as to leave the garden protected throughout the summer,” Parra recommended.
The use of this type of product allows to reduce leaf temperatures, avoiding premature stomatal closure and, therefore, the decrease in the photosynthetic rate. The benefit of sunscreens or protectors is supported by a series of investigations. Eduardo Parra, highlighted one of them: "the power to obtain or achieve a greater accumulation of starch at the level of darts, which has a very positive effect orA more mature dart when entering dormancy and more resistant to low temperatures during spring, along with promoting processes such as flowering in the following season, initial setting and proper and good development of the fruit”, he explained.
Correct photosynthesis and accumulation of reserves during post-harvest are essential for the following spring; remember that the beginning of root activity occurs only 20 to 30 days after flowering, therefore, during this entire initial period the plant is sustaining its metabolic activity solely based on reserves.
Zeroseven recommends the use of sunscreens or blockers in conjunction with other products that help to continue minimizing abiotic stress: “For example, seaweed extracts, and mainly, based on experience and all the associated work, those from the Ascophyllum genus are ideal; the combined use of kaolin and seaweed has been studied extensively, demonstrating the benefit of reducing thermal stress associated with a greater accumulation of reserves and, therefore, a better post-harvest and a better start to the following season.”, concluded Eduardo Parra.
Detecting, controlling and preventing abiotic stress in orchards are tasks that cannot be avoided, especially considering that the three factors: high temperatures, water shortage and high radiation, are increasingly frequent and extreme. It is necessary to keep orchards protected and conditioned to mitigate stress and thus improve production.
