Risk of Extreme Early Frosts in Almond

Abstract

In almond, late frost is the main factor determining the viability of the culture in cold areas, and late flowering remains the key factor in addressing this issue. Climate change is causing an increase in the frequency of extreme weather events. In 2021, the cold period in Spain after the Filomena storm (11–14 January), in which temperatures reached −20 °C in some regions, was a clear expression in this regard. In many almond-growing areas, these low temperatures affected the closed flower buds of most of the cultivars, except for the extra-late and ultra-late cultivars and despite the early stage of development of the buds, leading crop failure. In this work, we show that early extreme frost only affected the extra-early, early and late almond cultivars that had overcome their endodormancy and fulfilled 40%, 31% and 23% of their heat requirements for flowering. Extra-late (with only 2% of their heat requirements covered) and ultra-late (still in endodormancy) cultivars were not damaged. These results show the importance of cultivating extra- and ultra-late almond flowering cultivars to avoid not only the late frost but also the early frost during the very early development of the flower buds.

Reviewing the Adverse Climate Change Impacts and Adaptation Measures on Almond Trees (Prunus dulcis)

“…For Prunus dulcis, among the other parameters, orchard sustainability, yield viability, and production of high-quality fruits are susceptible to climate conditions [22,50,96]. The phenological stages may be affected by insufficient chill accumulation, heat waves, drought, irregular rainfall, and spring frost.…”

“…Another stress factor is spring frost during the flowering stage and fruit set, where mean temperatures under −2 • C are very likely to affect the viability of flower and fruit development and, consequently, the crop's economic sustainability [22,35,54]. Spring frosts can affect 40% of the flowering stage of early varieties.…”

“…Spring frosts can affect 40% of the flowering stage of early varieties. For this reason, it is important to develop late, extra-late, and ultra-late varieties to delay flowering until late spring, when frost is less likely to occur [2,22,98].…”

“…In the almond tree case, frost spring events have a higher impact on phenological stages, especially in flowering. According to Guillamón et al [22], late frosts can disturb ~40% of the flowering of extra-early and early varieties (such as "Desmayo" and "Marcona"). Additionally, changes in developing flower buds, pollinators' activity, kernel quality and structure, and productivity can be observed [35,128].…”

“…According to some studies, spring frosts can affect ~40% of the flowering stage of extra-early to early varieties, whereas the temperature increase can affect the durability and success of the chilling and forcing phases [2,22]. Moreover, in 2018, the Mediterranean basin countries produced only 29% of almonds under rainfed conditions.…”