Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Freezing temperatures are expected the night of April 2 throughout Delmarva. Cold damage in fruits is a concern.
Stone Fruits
Many peach, nectarine, apricot, pluot and plum trees are in in pink to full bloom currently. Research has shown that when these stone fruits are in the First Pink (or white) stage (flower petals coming out of bud but not open), the temperatures required to cause 10% and 90% kill at this bud development stage were 25°F and 15°F, respectively. At First Bloom, the temperatures required to cause 10% and 90% kill were 26°F and 21°F, respectively. At Full Bloom Stage the temperatures required to cause 10% and 90% kill were 27°F and 24°F, respectively and at Post Bloom Stage the temperatures required to cause 10% and 90% kill were 28°F and 25°F, respectively.
Peach from pink to full bloom stage.
Plum in full bloom.
Strawberries
For strawberries the critical temperature during bloom at the blossom level is 28°F. Below 28°F, there is a progressively higher risk of flower damage, and below 26°F most blooms will be damaged or killed. Flowers that are not open and just emerging from the crown can tolerate temperatures down to 22°F and once fruit has formed temperatures down to 26°F can be tolerated for short periods of time. Flower acclimation is also important. Plants with flowers exposed to several cold days before a frost will be more tolerant than those exposed to warm days before a frost. In addition, not all flowers in a field will have equal risk of damage. Flowers under leaves or near the soil will often be warmer than those higher on the plant or those more exposed.