Frost damage occurs when plant tissue is frozen. Freezing causes the plant’s cells to shrink, forcing water into spaces between the cells where it can freeze and form ice crystals. As temperatures rise and thawing begins the water is absorbed back into the cells by osmosis. If this occurs quickly there is no damage to the tissue, but if thawing is slow, the cells are deprived of water and become dehydrated resulting in ‘frost burn’.
Plant Part: Fruit, Leaves and shoots.
Season: Winter
Symptoms: Frosted fruit can have rind scald and dry fruit sacs. Severely damaged fruit usually drops off the tree. Young, frost-damaged trees can suffer bark splitting and foliage death. A succession of moderate frosts and cold winds can cause foliage curling and bleaching exhibited by brown coloured blotches on the leaves.
Cause: Leaves can be damaged (burnt) by exposure to cold conditions, damaging plant tissue. Young leaves are most susceptible to frost damage. Wind also increases cold temperatures via windchill and young trees should be protected from wind.
Internal fruit damage can occur when weather conditions are below -2 °C for more than four hours. There are varietal differences in susceptibility to frost damage. Mature fruit are less susceptible as the sugar acts as an antifreeze.
Management: Do not plant trees in areas prone to severe frost. Cover or protect trees from frost during Winter. Frost fans increase airflow from the warmer inversion layer to delay frost formation.
References: Australian Plant Society Victoria, NSW Department of Primary Industries , Citrus Plant Protection Guide 2020, and the FST team.
