Climate change, changes in production between seasons, changes in phytosanitary programs, changes in the frequencies of rot types… “Change” is the big word that we must adapt to and know how to read in order to be successful in the production of quality cherries. In this article, we will analyze these changes from a phytopathological perspective, what we have learned in recent years and how the monitoring tool is essential to stay one step ahead of pathogens.
In an article by January of this year, we reviewed how the behavior was, in terms of rots, of the 2023-24 season, where Botrytis was finally the most abundant pathogen, all this preceded by the rains during the ripening period of early varieties and some mid-season varieties, unfortunately affecting Santina, one of our main export cards from Chile. The rains generate cracks and/or small fissures that facilitate the infection process by the pathogen. Botrytis and the presence of free water facilitates their reproduction; thus, in pre- and post-harvest their detections increased considerably with respect to the most recent history. But as mentioned in the January article, other friends of their gang also appeared, and Geotrichum, an actor that had been irrelevant in the last dry years, took force; from flower we began to observe increases in its frequencies which ended in the appearance of sour rot in cherries and others. Prunus, such as nectarines and peaches.
What have we observed in recent years?
Figure 1 shows the dynamics of rots detected in symptomatic fruit samples that arrive at the laboratory each year. These are essentially post-harvest samples that have already gone through the packing process and are sent to Diagnofruit for pathogen identification. With this, clients can establish reports to producers and generate histories. Due to the nature of the sampling, all the information we can collect is exploratory and shows seasonal trends. As you can quickly see when looking at the table, this data is a clear example of climate fluctuations and the impact on the type of rots by season. Now, let's transform this data into information to better understand the changes in the weather. CHANGES.
The figure has a “memory aid” that marks in a very simple way how November and December behaved in the season analyzed in climatic terms; we can observe very dry and hot springs like 2020-21, and on the contrary, other humid and cold ones like the one just past; extreme cases like these allow us to observe details in the behavior of fungi that cause us problems that under a context of “normality” are more difficult to appreciate.
Now let us turn our attention to Alternaria, a fungus (strictly speaking, a complex of species) that causes black rot in cherries, generating the deepest headaches for producers and exporters. Clearly, it was the dominant rot from 2020-21 to 2022-23, bordering on detection frequencies of 45%. However, the reign ended in the last season where it appeared with personality Botrytis, which causes grey rot.
The presence of free water and milder temperatures are the perfect mix for Botrytis show us its super-pathogen qualities, characteristics that elevated it to the podium in 2023-24 with 35% detections. Botrytis or gray rot, is a problem that is always present, bordering on 10%, probably very contained with pre- and post-harvest fungicide programs, but the problem worsens depending on the climate as the monitoring data shows us.
Figure 1. Frequencies of rot detected in symptomatic cherry samples analyzed at Diagnofruit Laboratories by season.
Another fungus that is aided by the presence of free water and fissures in the fruit is Geotrichum, the causal agent of sour rot in various fruit trees, which this year we detected even in kiwis and hit us hard in various stone fruits. The driest season, 2020-21, was a fungus that almost disappeared with a frequency close to 1% of detections, then bordering on 10% until a rainy year where it rose to 17% and could probably have been higher; however, as we knew that the pathogen was present from early spring periods, we suggested the introduction of tebuconazole as a control standard in pre and post-harvest, which could largely contain the appearance of this pathogen in cherries.
On the opposite sidewalk, Cladosporium, causing dry green rot, is inhibited in wetter seasons; we can see that in the last campaign it tends to disappear and in dry years, such as 2020-21, it fights for the podium with Alternaria. We have learned that Cladosporium and Alternaria They are real partners; although Cladosporium It appears alone on fruits, it is very common that it is mixed with rots of Alternaria, sharing the ecological niche. Both are fungi that are very present in agricultural environments, develop or possess resistance to several fungicides, live inside plant tissues, which makes them very successful in terms of colonization. These characteristics do not always mean that there is rot, they live in the systems without causing disease, but eventually, if they encounter aberrations, such as poor ovary seal or growth splits (cv. Sweet Heart), they settle and then generate dry rots in the fruit development process. Both fungi tolerate drier and higher temperature environments, so much so that in the case of Cladosporium Even certain species are considered xerophilous (growing in arid and semi-arid areas).
Monitoring, data collection, information = SUSTAINABILITY
The exercise carried out and shown in this article, although it does not arise from standardized sampling according to the number of fruits analyzed (>1,500 per season), gives us a powerful image of what happens in the period and the availability of this information allows us to learn through historical analysis.
In a certain way, this exercise is carried out in the packing plants, with samples taken at reception and also post-storage, however, this data does not flow towards the construction of information and does not reach the producers. We have helped to perfect this type of analysis, training teams from the most important companies, they have begun to build FINE HISTORY what happens with their producers, which helps field agronomists to establish specific programs for those orchards with particular problems; but without a doubt, we still have a long way to go in a more standardized way.
Monitoring the presence of diseases should be an annual exercise, generating statistics by plot with harvest observations is a tool that each producer should have year after year and add what is generated by the exporter. These data should remain available for exporters' advisors and technicians in order to generate specific programs pointing to the sustainability of production in accordance with the land and climate reality and not with a recipe that has often been copied and with little technical sense.
Stay tuned for upcoming articles, because we will explore what happens with the fungicide resistance of these populations. Isolates from Botrytis, Alternaria, Cladosporium, Penicillium and Geotrichum from the last season were subjected to sensitivity analysis to the main fungicides used in cherry production; this other type of monitoring allows us to monitor the effectiveness of the molecules and at the same time know what type of active ingredients I should use in the face of observed climatic fluctuations, always thinking about being ONE STEP AHEAD OF THE PATHOGEN.
