What then are white and black frosts?
Frosts may also be referred to as white or black. This terminology is used to explain the weather conditions that the frost occurred. White frosts occur under high moisture conditions. The vine tissue being covered in ice crystals typifies these frosts. The crystals form due to water vapour condensing when the dew point is below 0o C. Black frosts occur under very dry conditions. These frosts are characterized by vine tissue being frozen due to an air temperature drop without sufficient water vapour in the atmosphere to form ice crystals. This frost is difficult to initially identify, as there is no white ice over the vine structure or on the ground before frost damage symptoms begin to appear on the vine.
