September came with intense frosts ...
The impact projection in the final production of blueberries is variable since the plantations observe different degrees of phenological state, from flowering, or end of flowering, to fruit set, or in process of maturation, in the case of the early fruit of the Northern Chilean regions.
Intense frosts hit the crops of several regions of Chile in these first days of September, mainly in the central zone. The damages are still incalculable, although in a first impression based on minimum data, but of first source, it can be concluded initially that for some producers the losses are very important, being able to alter even the agreed programs of deliveries and exports of blueberries of some regions , although the official information of the Committee of blueberries, in the Report of Frosts of the 6 of September, concludes that this will only affect the 4% of the national production.
The frosts extended from the IV region, encompassing the V (-1,8 C the 3 / 9); Metropolitan region (-1,1 C the 2 / 9), VI (-1,6 C the 2 / 9), VII (-4,2 C the 2 / 9), and VIII (2,8 C the 5 / 9). According to the report of the Committee, the lowest temperatures were registered in the commune of Longaví, VII region, where the minimums bordered the -4,2 º C on Friday 2 of September.
Impact on measurement
The impact of these frosts, both by the indices of the temperatures reached, and by the time they were extended in each geographical region is very unequal. Likewise, the projection of impact on the final production of blueberries is also variable since the plantations observe different degrees of phenological status, from flowering, or end of flowering, to fruit set, or in process of maturation, in the case of fruit early of the northern regions of Chile.
In the case of the regions to the south of the VIII Region of Chile, the impact would not have the same importance or effect, because the earliest varieties are in flower.
According to the Report of the Committee of blueberries, making an account of the progress of the phenological stages at the country level, the early varieties that are in curd and, therefore, are more vulnerable to this type of events, are mainly Jewel, Star and O'Neal, whose progress differs according to the production area. According to our sources, the Brigthwell, Legacy and Oclokonee varieties have also been affected in the VII region.
The report concludes that considering that only some sectors were affected by low temperatures, added to those orchards that have tunnel protection and anti-freeze control that reduce the damage, it is expected that the effect on early varieties will be low at the country level, not exceeding 4% of total area.
Frost damage
According to a study by the United Nations Food and Agriculture Organization, FAO, damage due to low temperatures can occur in all plants, but the mechanisms and type of damage vary considerably. Species or crop varieties exhibit different frost damage at the same temperature and in the same phenological stage, depending on previous weather conditions. Direct damage by frost occurs when ice crystals form inside the cell's protoplasm (freezing or intracellular frost), while indirect damage can occur when ice forms inside the plants, but outside the cells.
Hardening
Its adaptation to cold temperatures before a night frost is called "hardening".
During cold periods, plants tend to harden against freeze damage, and lose hardening after a warm-up period. The hardening is probably related to the increase of the solute content in the tissue of the plants, or with the decrease of the concentration of active bacteria in the nucleation of ice (INA in English) during the cold periods, or a combination of both of them. During the warm periods, the plants exhibit growth, which reduces the concentration of solutes, and increases the concentration of INA bacteria, making the plants less resistant.
Although cold temperatures cause the fruits of the plants to harden against frost damage, the hardening is quickly lost after a few warm days. The yolks of the fruits will harden again, but at a much slower rate than they have lost. This is the basis of the practice of cooling crops with sprinklers during the warmer periods of the day to reduce the temperature and avoid the loss of hardening.
Speed and intensity
The extent of damage due to intracellular freezing depends mainly on the speed of cooling and the intensity of cooling before freezing. There is little or no evidence that the duration of the freeze affects the damage. In fact, it is established that freeze damage seems to be independent of time for short periods. Direct damage by intracellular freezing is associated with rapid cooling.
Slow thaw
Although the evidence is not very large, according to the study, it appears that the rate of thaw after a freeze is partially related to the intensity of the damage. The study says that growers in Southern California usually believe that slowing down the heating process after a freezing night can reduce frost damage. In fact, the fruit growers justify the start-up of fans for longer in the morning after a night of freezing to slow down the process.
Source: Blueberry Committee, FAO, Blueberries Consulting
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