With just a few days to go before the month of May begins, ideally our cherry trees should have around 50 percent of their leaves fallen, evidence that they are in the final stretch of entering dormancy. Therefore, it is extremely important to have a clear picture of what is happening in our orchards; one of the most important aspects is the characteristic or condition of the fruit centers of our cherry trees.
“What should we see today? Well-closed shoots and bases of twigs, very well lignified, with well-formed bracts or, in the worst case, a hint of green tips that can be seen at this time of year, but that is not a big problem. What would we not like to see? Open shoots or green buds with a good percentage of green tips or almost ready to open. This not only presents a problem of the production potential that we could lose due to some early frosts, but also from a phytosanitary point of view, and I do not want to focus only on bacterial canker, but also on some wood fungi that afflict us and that are present and that we, the cherry world, are not used to seeing or detecting; Cytospora is one of them and that has been in fashion lately and it seems that we have started to see it in the fields of colder, more southern areas,” explained Carlos Tapia, cherry production specialist and Technical Director of Avium.
About gender Cytospora Unfortunately, there is not much information, however, according to Hector Garcia, Founder and General Manager of Diagnofruit Laboratories, the first bibliography dates back to 1818, when it was defined as "endophytic fungi, tearing dead wood without pathogenic character"; later they were characterized as a disease: "it was determined in a generic way Cytospora, but it is also known as perennial canker, raft or leucospora and more than 85 woody fruit plants have been described as hosts of this type of pathogen, including cherry trees," explained García.
According to experts, the current phytosanitary management of orchards and climate change itself could be the main causes of the reappearance of this fungus, which unfortunately, if not detected and treated appropriately, can cause considerable damage and even the death of cherry plants.
Although the above is of utmost importance, we must not lose sight of the main objective of this time of year in our cherry orchards: to ensure that physiological dormancy in the plants begins to appear naturally.
Carlos Tapia, an expert advisor on cherry cultivation, explains what physiological dormancy is and how to detect it: “It is the moment when the plant crosses the 50 percent line of leaf fall, always considering yellow leaf to be equivalent to fallen leaf and that in some way marks us and tells us that the plant is sleeping, not deeply yet, because the stages of dormancy are different, but that it has already entered a period of latency, of dormancy; we have to be able to see this, analyze it and make decisions; if we see today the orchards very green and very active in terms of leaf color and vegetative expression, not necessarily growing, we have to make decisions to try to speed up this dormancy or invite the plants to shed their leaves, unfortunately, not naturally,” concluded Tapia.
Remember that this state should naturally be present in the first days of May, while the evaluation of the orchard in terms of leaf fall should have been carried out between April 15 and 20. If it is detected that there is no sign of leaf fall, a chemical solution should be applied to artificially speed up this important process.
“This is where one of the practices we are most used to is introduced, which is the application, using the 'sulfate' poisoning model, in the most classic case we use Zinc Sulfate, mixed with urea, in which this mix together causes the sulfate to generate the poisoning effect and the urea enhances the decomposition of the leaf, and in this way the leaf begins to fall, not normally, but artificially, but we are achieving what we want,” explained the Agricultural Engineer, M. Sc, Carlos Tapia.
The fall of 50 percent of the leaves marks the beginning of the physiological dormancy of the plants; ideally this should coincide with the first week of May, when climatically there is the possibility of counting the hours of cold that are useful for the plants, a fact that is relevant only if the orchards have crossed this 50 percent of leaf fall.
After this, the concern should focus on the management of fall-winter phytosanitary programs: “The use of copper-based products, which are today a classic in fall-winter management, are involved in the first stage by covering all the natural wounds that occur as a result of leaf fall, therefore we have two or three applications that we have to do as the percentage of leaf fall advances and then, through some type of rigorous program thinking about spending the winter in the central zone, perhaps, applications every 25 - 30 days, being able to repeat these applications after a frost event rather than rain, until reaching swollen bud, with swollen bud being the last application of the winter program, but also the first of the spring program,” explained advisor Carlos Tapia.
Another point to consider is that, although the plants are entering a period of dormancy, they are not dead, but are in a stage in which their metabolism, both vegetative and root growth, is practically zero. It has been proven that below 7ºC of soil temperature the roots have practically no development, between 7ºC and 15ºC they generate an imperceptible movement and above 15ºC of soil temperature, the roots develop rapidly.
“Although the roots are not active in winter, they are alive and these roots cannot dehydrate. In recent years we have not had to worry much about this aspect, because winters have been beneficial from the point of view of normal rainfall in the central area. However, in the last two or three years we have seen a very significant break in rainfall and that in some way makes us reconsider the option of whether we have to irrigate in winter or not. My proposal, in super extreme terms, putting ourselves in the worst case scenario of no rain this winter or very little rain, is that we do have to propose a model for maintaining soil moisture, to prevent the roots that were generated in the last season from dehydrating and dying,” warned the Technical Director of Avium.
It should be remembered that the roots generated in the recent season are extremely fine and contain a large part of the nitrogen reserves from the last post-harvest; in addition, they are the most effective and efficient in capturing water and nutrients in the first stage, but at the same time those with the greatest dehydration power.
“How much do we have to water in winter when there is a climatic catastrophe in terms of a lack of rain? Nothing has been studied very well, but I think we have to try to maintain a certain soil humidity, at least 20 to 30 millimeters of replacement irrigation per month, to the extent that through some information search model, test pits, sensors or a mixture of both, we can establish that we have a soil humidity that, although it is not used as much by the plant, is a humidity that allows me to maintain the water condition of the roots and avoid dehydration,” said Carlos Tapia.
It is necessary to anticipate and monitor this situation, taking into account the specific irrigation conditions of each producer. To do this, it is important to plan a winter irrigation model, in the absence of rain, that prioritizes the correct distribution of water rather than the quantity of water, simulating the effect of normal rainfall.
