Fruit Tree Critical Temperatures

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The temperature at which fruit buds are injured depends primarily on their stage of development.

As flowers begin to swell and expand into blossoms, they become less resistant to freeze injury. Not all blossoms on a tree are equally tender. Resistance to freeze injury varies within trees as it does between orchards, cultivars, and crops. Buds that develop slowly tend to be more resistant. As a result, some buds are usually killed at higher temperatures, while others are resistant at much lower temperatures.

The table below shows the average temperatures required to kill 10 percent and 90 percent of buds if they are exposed for 30 minutes. Consideration should also be given to weather conditions preceding cold nights. Prolonged cool weather tends to increase bud hardiness during the early stages of bud development.

Adapted from 1989 Spray Guide for Tree Fruits in Eastern Washington. Bulletin EBO419. E. H. Beers, coordinator.

Apples

For Red Delicious. Golden Delicious and Winesap are approximately 1 degree hardier. Rome Beauty is 2 degrees hardier, except after petal fall when all cultivars are equally tender.

Stage of Development 10% kill (°F) 90% kill (°F)
Silver tip 15 2
Green tip 18 10
½-inch green 23 15
Tight cluster 27 21
First pink 28 24
Full pink 28 25
First bloom 28 25
Full bloom 28 25
Post bloom 28 25

Peaches

Stage of Development 10% kill (°F) 90% kill (°F)
First swelling 18 1
Calyx greeg 21 5
Calyx red 23 9
First pink 25 15
First bloom 26 21
Full bloom 27 24
Post bloom 28 25


Pears

For Bartlett. D'Anjou is similar but may bloom earlier and therefore may be more tender than Bartlett at the same date.

Stage of Development 10% kill (°F) 90% kill (°F)
Scales separating 15 0
Blossom buds exposed 20 6
Tight cluster 24 15
First white 25 19
Full white 26 22
First bloom 27 23
Full bloom 28 24
Post bloom 28 24

Sweet cherries

Stage of Development 10% kill (°F) 90% kill (°F)
First swelling 17 5
Side green 22 9
Green tip 25 14
Tight cluster 26 17
Open cluster 27 21
First white 27 24
First bloom 28 25
Full bloom 28 25
Post bloom 28 25

Apricots

Stage of Development 10% kill (°F) 90% kill (°F)
First swelling 15 -
Tip separated 20 0
Red calyx 22 9
First white 24 14
First bloom 25 19
Full bloom 27 22
In the shuck 27 24
Green fruit 28 25