Frost is an important climatic phenomenon in agriculture due to significant productivity losses or the plant die, depending the intensity. In meteorology, frost occurs when there is ice deposition on the plant exposed to the outdoors, in which the air temperature reaches 0ºC and has humidity in the atmosphere (PEREIRA, 2002). However, even with the formation of ice on the plant, there can be no death of the plant tissues, because they are in vegetative rest.
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The susceptibility of the plant to frost depends on the agricultural crop and the phenological stage. According to Mota (1981), crops less resistant to frost, such as banana, papaya and rice, consider that -2°C is the minimum critical temperature in the leaf that initiates damage to plants. For the most resistant crops, coffee, sugarcane and citrus, the limit is -4°C. As the minimum temperature reaches lower values, the more severe the damage.
In Brazil, the frost is a frequently phenomenon during the winter in latitudes above the parallel 19°S, involving the states of Minas Gerais (Mining Triangule and south region), Sao Paulo, Mato Grosso do Sul, Parana, Santa Catarina and Rio Grande do Sul. There is chance of occur early frost, in fall or late spring, when damage to crops intensifies, which intensify crop damage.
Frost can be monitored in one location by tracking the minimum temperature in a weather station, indicating conditions for frost when they reach the values in the table below.
| Minimum temperature in the weather station | ||
| 4ºC (crop more resistant) | 2ºC (crop resistant) | 0ºC (crop less resistant) |
| Banana, potato, beans, vegetables, papaya and tomatoes. | Cofee, sugarcane, mango and wheat. | Orange, apple and pear. |
Source: CPTEC
According to Camargo (1972), there are two types of frost that define them in relation to their origin or visual effects.
Regarding its origin:
- Frost of cold wind: caused by strong constants winds and with low temperatures, occurring the leaf dryness and consequently its death. There are situations where damage to the plant occurs on one side only;
- Frost of radiation: occur in nights of clean sky, no clouds, no winds, with low moisture and cold air. In this case, the temperature of surface gets lower than the air temperature, called thermal inversion;
- Mix frost: frost when the both processes successively occur, that is, entry of cold and dry mass, and subsequent intense nocturnal radiation loss.
Regarding the visual aspect:
- Black Frost: there is no ice deposition in plant in this type of frost, due to low air moisture. This type of frost is more severe, because the low moisture allows lower temperatures to occur, leaving the plant dark in color;
- White frost: when the moisture present in air condenses, and then freezes, ice deposition occurring on the plant.
Places of highest occurrence of frost
- Latitude: in Brazil bigger latitudes than 19°S there is chance occur frost, with large frequency in winter, damaging tropical crops, like coffee, citrus and banana. Regarding to temperate crops, it are not affected by winter frost as they are in the dormant stage. On the other hand, early frost (fall) affects the flowering, and the late frost (spring) affect the fruiting.
- Altitude: as higher altitude, the temperature is lower, and consequently the greater the occurrence of frost.
- Topography: lowland areas are more susceptible to frost formation, due to cold air be denser than heat air. Another type of topography is south-facing terrain, where it is less exposed to the sun during winter.
During the months of May to August, DATAGRO monitors the chance of frost occurring in sugarcane fields in the Center-South region, and it is possible to follow up on DATAGRO’s Climate Alerts.
References:
MOTA, F. S. Meteorologia agrícola. São Paulo: Nobel. 1981, 376p.
PEREIRA, A R., ANGELOCCI, L.R., SENTELHAS, P.C. Agrometeorologia: fundamentos e aplicações práticas. Guaíba: Livraria e Editora Agropecuária, 2002. 478p.