Accumulation of winter cold in northern Argentine Patagonia

Argentine Northern Patagonia is a fruit-growing region of world-renowned prestige, both for its long history in the agro-export industry and for its exceptional agro-environmental conditions for the production of fruits with a temperate-cold climate. The latter, of a Mediterranean-continental type, with cold winters and warm, dry summers, characterized by a high thermal amplitude, added to the abundant availability of meltwater provided by large rivers, allow us to bring together not only the attributes that determine a great difference in quality in the cherries produced here, but also define an extraordinary health context, characterized by a low or zero incidence of pests and diseases, a fact that is demonstrated, for example, by the recognition of the region with the status of “Fruit Fly Free Area” by the United States, China and Chile.

Understanding dormancy as a key stage within the annual cycle that the cherry tree must go through to reach a satisfactory productive potential, it is possible to validate and verify that these agroclimatic attributes of this region allow to consistently meet the needs required in this very important rest period. In this sense, and shifting our focus to the transition or acclimatization that the fruit tree experiences during the late post-harvest phase, in what we define as "entering dormancy", which typically takes place during the month of April, the cherry trees planted here show a marked evolution in leaf senescence ("yellowing"), which occurs naturally in the face of the progressive drop in temperatures and the occurrence of the first frosts of the year, reaching the end of that month with more than 50% of fallen leaves in all varieties, which in turn allows an early accumulation of cold to begin, and avoids or dispenses with the application of strategies for the artificial induction of leaf fall, as occurs in other producing regions of the southern hemisphere, and also makes it possible to begin winter pruning work early. The latter is not a minor aspect if we take into consideration the current context of limitations in the availability of labor that the fruit sector is going through, allowing to compensate or counteract the lack of personnel, with an extension in the time window for carrying out this very important work, and which, as we well know, has a limited period in time for its fulfillment (Figure 1).

   Figure 1: Progress of entering dormancy in a Lapins variety orchard, located in the Vista Alegre area, Neuquén.

Focusing our analysis on the accumulation of cold during the current year, it is possible to infer that, to date, the accumulated records show a trend of accumulation slightly higher than the historical average (2003-2022 series), both in terms of hours of cold (conventional method base 7.2 °C), and in cold units (Utah model / Richardson et al., 1974), and slightly lower than what happened for the same date during the previous year, characterized by an exceptional accumulation of cold (EEA INTA Alto Valle, 2023). 

To express in numerical terms what has happened until today, July 17, we observe that for the town of Vista Alegre (Neuquén), the accumulated values are 816 HF and 766 UF. These records imply an increase of between 3.9 and 6.4% compared to the years 2019 and 2021, and a decrease of between 7.4 and 21.3% compared to 2020 and 2022 respectively. The accumulation of cold recorded to date complies with the entire requirement for the varieties Royal Dawn, Lapins, Santina, Skeena, Sweet Heart and Bing, leaving only Regina pending, if we consider the main cultivars planted in this region. The values relative to this current situation, as well as in relation to the 4 previous seasons, are shown below (Tables 1 and 2).

Table 1: Cold accumulation (Base methods 7 °C and Richardson) for the town of Vista Alegre, Neuquén as of 07/17/2023.

Table 2: Percentage of cold accumulation of the main varieties cultivated in Northern Patagonia, for the town of Vista Alegre, Neuquén, as of 07/17/2023.

This accumulation potential, specific to the region, also allows for independence from the use of dormancy breakers to compensate for the lack of cold, as occurs in other areas that are particularly early in the harvest calendar, with this application being more strategically focused on synchronizing flowering curves between self-sterile varieties and their pollinators, and on attempting to advance flowering (and eventually harvest) dates, as long as the spring thermal accumulation counterpart (degree-days from bud break) is significant enough to allow for this effect.

*Vista Alegre SRL technicians members of CAPCI – www.capci.com.ar, for Smartcherry.