On Monday, April 4, 2016 9:16 AM, Tara A Baugher <ta...@psu.edu> wrote:
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{margin-bottom:0in;}-->Growers – a number of you have been asking about
potential impacts from the freezing temperatures already experienced and in the
forecast, so I’ve pasted in Rob’s fact sheet from thePenn State Extension Tree
Fruit Production website. Note that prolonged cool weather tends to increase
bud hardiness during the early stages of bud development. ~Tara Critical
Temperatures for Various Fruits 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.
Examples of stages of fruit bud development: top left - apple tight cluster;
top right - apple pre-bloom; lower left - sweet cherry first white; lower right
- peach pink. 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.
| Stage of Development | 10% kill (°F) | 90% kill (°F) |
| |
| Applesa |
| 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 |
| First swelling | 18 | 1 |
| Calyx green | 21 | 5 |
| Calyx red | 23 | 9 |
| First pink | 25 | 15 |
| First bloom | 26 | 21 |
| Full bloom | 27 | 24 |
| Post bloom | 28 | 25 |
| Pearsb |
| 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 |
| 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 |
| First swelling | 15 | - |
| Tip separates | 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 |
Adapted from 1989 Spray Guide for Tree Fruits in Eastern Washington.
Bulletin EBO419. E. H. Beers, coordinator.
- 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.
a. For Bartlett. D’Anjou is similar but may bloom earlier and therefore
may be more tender than Bartlett at the same date. Source: Penn StateTree
Fruit Production Guide. (Updated January 2016). Contact Information Robert
Crassweller
- Professor of Tree Fruit
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