Fruit Tree Critical Temperatures
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.
Contents
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 |
