In recent weeks, exporters, agrochemical companies and producers have asked me for guidance on how to best deal with everything that meteorologists predict and that could cause us problems in the current cherry season. Thus, the following article aims to highlight the main aspects to take into consideration if bad weather occurs, but, at the same time, to ensure that a positive attitude is able to prevail for successful production.
The scenarios
According to what we read and are informed through various channels, El Niño would be the main risk factor for this campaign, added to all the imbalance generated by climate change. These climatic phenomena make us suppose at least three possible scenarios (Fig. 1); obviously there could be fewer problematic situations or more if the different scenarios occur in tandem. The first scenario is rain in early spring, flowering, which could result in various problems associated with blight and poor pollination. The second scenario is rain in the final third of spring, when much of the fruit already has a state of maturity that makes it susceptible to cracks and infections; and a third scenario that has to do with powerful heat waves projected for the summer, which if they begin in December (eventually before) could impact the quality of the fruit and other factors that we will detail later.
Figure 1- Possible scenarios for the 2023-24 season and probable phytopathological and productive consequences.
Rains in flowering, breeding ground for blight
Early spring rains could cause some problems in the awakening of our cherry trees, but, especially, the most serious problems would be in the flowering process. There are three diseases that can give us battle, flower blight caused by fungi, Botrytis I, Monilinia, bacterial blossom blight (Fig. 2) and canker, both diseases caused by Pseudomonas pathogenic.
In my opinion, the phytosanitary programs we developed in Chile protect flowers well against fungal blight (it is difficult to see severe attacks); a series of 2 to 3 (even 4) applications of fungicides, considering various groups such as triazole, carboxamide and phenylpyrrole, generate very effective protection against these attacks. However, in wetter seasons, such as the recent one, it was possible to detect blossom blight caused by Pseudomonas (see previous article).
For this reason, in some way, the flowering period must be reinforced with applications that seek to lower the inoculum load of Pseudomonas, antagonists like Bacillus, botanical extracts with a known effect on bacteria such as tea tree, or if the problem is increased use of antibiotics, should be considered. In the event of a blossom blight attack, we could end up with a plant developing bacterial cancer, in addition to inhibiting the fertilization process and therefore lower productivity.
Figure 2. Cherry blossom blight caused by Pseudomonas.
Straw-colored rain
Logically, this is, without a doubt, the worst scenario for our cherries. This fruit is generally very noble, obviously there are always orchards with dry rot or other rots that complicate production, but it is not the norm. These positive characteristics end when rainfall falls, generating an extremely different reality. Everything that involves the cracking process that finally comes down to the cherries being left with an exposed wound, resulting in an exponential increase in susceptibility to attacks from Botrytis and other fungi such as Geotrichum and Penicillium which facilitates the colonization process and subsequent development of rot.
From this perspective, the first concern is attack the splitting process (see previous article). The second thing is prevent rot, it is important to schedule a fungicide application in advance of the rains, we must always leave a window for the active ingredient to interact with the fruit and provide protection once the rain falls. Then we can continue with the pre-established program and eventually reinforce with botanical extracts, Bacillusso some multi-site fungicide that is allowed according to the tolerances of the destination market. As a general recommendation, when these events occur, the system becomes more complex, the waiting times of the fruit for packaging become longer and there is more inoculum contained in the process waters; considering this, an application very close to harvest of some formulation containing fludioxonil is very appropriate for a complex situation, in this way the cherries that see their waiting window for processing increased will present a better performance.
Increasing calcium and decreasing nitrogen in the fruit is a task that takes place every season, but if this dark scenario occurs, the mineral balance characteristics of cherries can determine the success of production under an adverse environment.
Extreme heat waves during harvest and post-harvest.
While we should continue to face precipitation in the short term, in the global context, July 2023 was the warmest July on record, according to information from NOAA (Fig. 3). Much of the planet had warmer temperatures than the historical average for the same place and period, and another, not insignificant portion, had record temperatures. This resulted in heat waves that have hit much of the northern hemisphere hard, leaving in their wake highly stressed crops, fungal attacks on crops, and uncontrolled fires. As a closer example, South America had a record July, with the highest monthly temperature anomaly ever recorded, 2.19 °C above the historical July average. Is the same scenario awaiting us? For our sake, we hope not, but models point to the development of heat waves with temperatures that could rise above 40ºC for the summer period in some areas of the central zone.
Figure 3. Ocean and continental temperatures in July 2023, prepared by National Centers for Environmental Information (NOAA)
If extreme heat waves begin in spring, the quality of the fruit can be greatly affected, accelerated maturity, stressful harvests, ending with fruit susceptible to problems such as bruising, pedicel dehydration, softening, among others. Fungi such as Cladosporium and Penicillium Their attack frequencies also increase, supported by their ability to develop in dry and warm environments.
Now, if extreme temperatures occur during the summer, the post-harvest period will require enormous care. The work must aim to keep our plants well hydrated and we must use all available tools to reduce stress during this period. Regarding diseases, remember that, although the conditions do not give rise to bacterial cancer, the scenarios could be capable of generating wood fungus infections such as Cytospora and CalosphaeriaFor this reason, green pruning, sanitary pruning, and other handling that generates wounds must be accompanied by chemical or biological control, paints for thick cuts and reinforcement with sprays for thinner cuts. Elicitors before leaf fall is an alternative reinforcement that should be considered.
Monitoring, the tool for decision making
Whether or not it will be a complex season in terms of diseases, we hope not; however, we must be prepared. Observation of the orchard accompanied by data collection, monitoring of inoculum, presence of symptoms, reinforcement of phytosanitary programs, must be activities that must be planned from now on, the attitude must be absolutely PREVENTATIVE and disease monitoring is a fundamental basis for the success of a complex season.
