By: Matías Kulczewski B. Agronomist, KyR Consulting, POMANOVA Corporation.
Carlos Tapia T. MSc agronomic engineer, Avium, POMANOVA Corporation.
Fluctuating production and its predictability deficit is a fundamental aspect of cherry production.
This season has been marked by indicators that raise fears of a lighter final setting; among these, the summer with attacks of spider mites and with a deficit of irrigation water, the high temperatures in summer and autumn and the lack of winter cold, are factors to take into account when considering field management in order to achieve a potential of production.
However, the analyzes of buds in progress are showing a relatively normal situation in terms of availability of floral primordia and there are again several cases of abundance of healthy floral primordia per fruit center (over 18-20 primordia), which invite us to review and consider crop thinning options.
Considering the above, we have considered it opportune to review a very complete investigation that we carried out in conjunction with the University of Washington State, represented by its extensionist Karen Lewis and sponsored by American funds. This work was presented at the IFTA (International Fruit Tree Association) Conference in the summer of 2012, which was organized by our beloved POMANOVA Corporation in Santiago de Chile.
That season, research was carried out whose main objective for the North American reality was to evaluate a prototype of a portable equipment for mechanical thinning, while for our industry and for the cherry world in general, the objective was to evaluate the effectiveness of the different opportunities for thinning offered by the crop in terms of production, quality, labor required and costs.
As we know, the realities of overproduction risks are very particular to each plantation, where the variety, rootstock, pollination and the still imponderable weather are the main determinants. However, even in less benign climatic years like the present, experience has taught that overproduction is more to be feared than lack, since it takes care of itself, especially in the cherry business.
Research and results
In 2 orchards with a history of thinning, one of Lapins/Maxma 14 in Sagrada Familia, Curicó and one of Sweetheart/Maxma 14 in Romeral, both in central axis at 4.5 x 2.5 m, manual bud thinning was studied. , mechanical thinning with portable equipment in 2 opportunities within flowering (20 and 80% flower), manual thinning in flowering (80%) and fruit thinning prior to stage 2 of stone hardening, approximately at “fall of jacket”, 21-22 DDPF. All compared with an absolute witness without any load regulation work.
The treatments were normalized in winter pruning and were homologated in thinning intensity, adopting the manual thinning of buds as a guideline for the intensity adopted in the remaining treatments. This meant doing many counts in the 3 plots of 2 trees (6 replicates) of each treatment.
The portable mechanical thinning equipment used was that of figure 1, whose jacket-shaped battery used by the operator is charged overnight and lasts a few hours, so it is convenient to have a double set of batteries for a commercial scale operation. elderly.
Figure 1. Used portable mechanical thinning equipment
Table 1 below shows the yields and size of fruits, illustrating that all types of thinning were effective in these orchards with high fruitfulness. In it, it can be seen that bud thinning was the most effective, but that the more retarded fruit thinning was also effective in recovering caliber of these overloaded trees.
Table 1. Productive results (kg/ha and kg/ASTT) and average fruit weight (g) for each thinning treatment in cvs. Lapins and Sweetheart.
For their part, the resulting size distribution curves “speak for themselves” (Fig. 2 and Fig. 3).
Figures 2-3. Distribution of calibers according to load regulation treatment for Lapins and Sweetheart varieties.
When analyzing hard data on the quality of the fruit in the different treatments, it can be shown that the most affected indicator is soluble solids (ºB), but not durofel, as is often logically thought, since it has a higher load potential (table 2).
Table 2. Soluble solids (ºBrix), Durofel and % discard of export fruit according to thinning treatments for cvs. Lapins and Sweetheart.
This result has been consistent in several other experiences, including other thinning studies, as well as the comparison between orchards and “extreme” experimental trees in the year 2017 of the “harvest” of Chile (table 3). As in the previous investigation, this one shows that – together with size – the quality characteristic most affected by the load are soluble solids (ºBrix), which give the fruit sweetness (and acidity), but not its firmness. In this regard, it should be remembered that acidity is important in the cherry’s storage longevity, for this reason an overload is very detrimental for our cherries, whose business is based on being able to run a marathon to distant markets.
Table 3. Numerical comparison between an orchard with thinning and a control without thinning in a high fruit set season and its effect on some productive and quality indicators. Source: M. Kulzcewski, personal information.
As fruit with “100 m race. flat and with fences”, the cherry has quite short times to diagnose, decide and execute its thinning, which, in addition, due to its small size is highly intensive in need of labor.
For this reason, it should be remembered that pruning is the first and most important thinning of the year that we recognize, that fruit set is one of the events that has the greatest unpredictability in cherry tree cultivation, and that many farmers justifiably fear climatic accidents, arguing also that this or that plantation “is very astonished” as to thin it out. The problem arises in loader variety/rootstock combinations and with over 18-20 primordia per fruit center, as occurs again this year in several cases reported by bud analysis. The topic “setting” is for another article, but in this experience we measured from 20 to 40% of set and only 10 to 15% of “pasma” after thinning and always less where thinning had been done than where it had not. In cases such as those of the reported investigation and any plantation of the species, the deadlines to carry out thinning in flowering and in fruit set are very short (normally no more than 7 days in each case) and with high requirements for labor and supervisors. .
Table 4 shows the labor requirement of the experimental treatments, highlighting the economy of the technique with portable equipment evaluated and the high labor requirement of all the rest, although with the advantage of a longer period (at least 4 weeks). -20 days) in bud thinning, which also stood out for its superior efficiency. It is considered that in the rest of the treatments they should only be carried out within 7 days. In the case of the need for people to carry out each treatment, it is considered that a working day is equivalent to 7.5 hours.
Table 4: Comparison of the time required (hours/ha) to carry out each thinning treatment and the need for labor (persons/ha).
As can be seen in the table and as we have also experienced in many cases besides this one, the number of people necessary for thinning cherries when there is high fruit set is very difficult, making it quite difficult to execute and control when it is postponed to flowering and even more so. to fruit set This should also be considered according to the effectiveness to meet the objective of each work, and in this sense, the research presented shows that, although the thinning of buds is an expensive task, it is undoubtedly the most effective and objective when deciding the intensity of thinning, allowing it to be carried out earlier and in a longer term, also with a greater and better possibility of having a permanent supervision of the work.
Due to all of the above, our proposal for “curdling” cases is progressive thinning, which starts with more intense pruning, continues with bud thinning and can be supplemented with flowering thinning to correct where “pom-pom” flowering is observed. too dense, relegating the thinning of fruits only to correct an still unpredictable excess of fruit set, which, although it does not seem to be expected this year, there will surely be cases in which it can happen.
It should also be noted that, as a “100 m hurdles race”, the cherry one requires a continuous look at the orchards, at least a couple of times a week, from now on when the bud is swollen.
Look to the future:
The short deadlines and the growing shortage of labor for the execution of intensive work in the field invite us to reflect on new projects.
Within these, the choice of varieties and productive rootstocks is a necessity, which with the numerous technological advances to protect the crop and better ensure its production, will generate more frequent situations in which overproduction threatens quality, as the main attribute of sustainability. of this business.
The path of less productive vigorous rootstocks has not been the best to ensure productivity in the reality of our country, but there are more frequent realities of excess production within fruit centers, as well as others where this problem only appears in years of high curd However, it must also be noted that when rootstocks of greater vigor (and greater youth) are used, well treated based on this characteristic, high productions have been achieved, of good quality and condition sustained over time.
In this regard, it should also be noted that the tests with chemical thinning in cherry trees have been inconsistent, easily going from lack of efficacy to over-thinning, which is why it is still a far-developed technical solution.
Considering the natural uncertainty of fruit set and the diverse realities in terms of climatic risk, it is advisable to adopt a progressive thinning system, which starts with pruning with the support of counts and bud analysis, and continues through the stages of bud thinning. flowers, the thinning of flowers and the thinning of fruits, with greater support from mechanical and chemical methods that make it possible to avoid the excessive need for labor in a very short time.
We take advantage of leaving this technological challenge posed for the next few years in our flourishing cherry tree industry, where the choice of conduction systems that are easy to intervene, with simple branches in 3D systems and/or with thin crowns in 2D systems, is likely to be an ingredient. important for this reality, that many times we do not have it considered when choosing the conduction systems in the new cherry tree projects.