Frost/Freeze Injury to Tree Fruit

May 10, 2001

On the mornings of May 7 and 8, 2001, a widespread frost/freeze may have damaged many tree fruit crops in Massachusetts, Connecticut, and Rhode Island. Overnight low temperatures were reported in the 22-30 F. range. Although a frost was predicted, the widespread nature, extended period below freezing, very low temperatures, and low relative humidity resulted in significant petal browning and bud injury when apples were mostly at the vulnerable full-bloom or petal-fall stage.

According to the Washington State University 'Stages of Apples' fact sheet, a temperature of 28 F will result in 10% bud injury to apples in full bloom. A low temperature of 25 F will kill 90% of the buds. Clearly, many Massachusetts, Connecticut, and Rhode Island orchards experienced low temperatures in this range. Indeed, reports from around Massachusetts indicate apple bud damage in the 10 to 90% range, depending on block elevation, stage of bloom, and height in the tree.

Growers are advised to do an assessment of the injury by cutting a sample of buds in half to see if the developing fruitlets have been damaged. Freeze-damaged buds will be visibly brown or black (24-48 hrs. after the frost) in the center of the fruitlet, while uninjured fruit will be completely green. Because frost/freeze injury can vary widely within an orchard depending on block location, cultivar, and height in tree, blossom buds should be examined throughout the orchard.

If bud injury is light (less than 30 % brown, damaged buds), the potential for a good crop is certainly still there. But, if injury is in the moderate to severe range ( greater than 30 %) growers must keep a close eye on the important fruit-set period following petal fall. Certainly, significant frost/freeze injury (>50%) will make thinning decisions more complex, and if the freeze results in significant crop reduction, then you may want to look at options for controlling growth for the growing season.

Keep in mind you only need to set 10% or less of all fruit buds to have a full crop. Although the frost/freeze damage is potentially significant, only time will tell how the southern New England apple crop will pick out come harvest. But we will keep our fingers crossed!

Note: for an interesting discussion of frost/freeze impact on fruit crops, see 'Principles of Freeze Protection for Fruit Crops' at the Alabama Cooperative Extension System.

Watch a short web video describing the frost damage (QuickTime player required, 8.2 MB)