Various parts of stone fruit trees can be damaged or killed by a late winter or spring frost or freeze.

Identification

If cold weather has occurred during late winter or spring, flower buds can be cut open and inspected to determine if they were damaged. Cold-damaged tissue develops a characteristic black or dark brown color. Stone fruit flowers can be cut or torn open to inspect for browned or blackened pistils. Flowers having black pistils indicate the flower has been killed and fruit will not develop from it.

If fruit were present during the cold, they can be cut open to inspect for black or brown lesions around the embryos (immature seeds). The center of the developing, young fruit should be green, not brown. An internally brown fruit is a dead fruit and it will likely fall off the tree and not mature.

Damage

A frost or freeze can kill blossoms, fruit, and leaves and cause shoot dieback and browning around the seed coat. Cold-damaged young fruit may drop. The extent of cold damage is directly related to how cold temperatures were, for how long, and the stage of flower bud or blossom development.

Solutions

To reduce the likelihood of frost injury, keep any cover crop or other vegetation under trees mowed short so that the soil surface is more exposed and firm. Unless soil is soggy, irrigate trees several days before cold temperatures are expected. These practices increase the soil's ability to absorb heat from sunlight and radiate the warm at night to help keep the trees warmer.

When a freeze or frost is predicted, if the trees are small enough to make it feasible, covering them in the evening with blankets, frost cloths, or nonplasitc tarps can help keep plants warmer. Leave covers open at the bottom so heat from soil can rise up and help warm the plants. Remove covers during the day.

If freezing weather is predicted, covering plants alone is of little help unless a heat source is provided. Placing incandescent lights designed for outdoor use in the canopy may generate enough heat to prevent the plants from freezing if the plants are also covered. Be sure not to create hazards of electrical shock or fire.

References

Adapted from Evaluating Tree Fruit Bud & Fruit Damage from Cold, Colorado State University; Freeze Damage to Local Fruit Crops, North Carolina State University; and Integrated Pest Management for Stone Fruits, University of California Statewide Integrated Pest Management Program (UC IPM).