What temperatures cause cold damage to peach flower buds?

Answer: In general, the stage of development of peach flower buds has a profound impact on their susceptibility to cold injury.  Dormant buds that are tight with bud scales intact are the most cold resistant while uncovered open flowers are least cold resistant.  As flower buds progress through the natural development process in response to warm temperatures in the springtime, each subsequent flower stage is more vulnerable to cold injury.  In fact, the temperature that is required to cause injury actually increases – i.e., more developed flower buds are killed at warmer temperatures.

In the early 1970’s, Washington State University published a series of bulletins noting critical temperatures for flower buds for several important temperate fruit crops.   Extension Bulletin 0914 “Critical Temperatures for Blossom Buds: Peaches” by Ballard, Proebsting, and Tukey illustrated the various flower bud stages and presented data for ‘Elberta’ noting the average temperatures required to kill 10% and 90% of the flowers, respectively, as observed at the Washington State University Research and Education Center in Prosser over seven years (1964-1970).  This publication is no longer in print.

Noted below are photographs depicting the common flower development stages that we observe with peach.  All photos were taken in South Carolina but they are not for ‘Elberta’.  In the caption for each photo, the relevant data taken from WSU Bulletin 0914 for ‘Elberta’ is noted to serve as a rough guide to show sensitivity to cold injury by flower stage.  It is relevant to note that flowers are typically not injured at the freezing temperature for water (32 F).  However, when flowers are at their most vulnerable stage (full bloom – postbloom), just a few degrees can make a very significant difference between only 10% loss (i.e., 28 F) and 90% loss (i.e., 25 F).  Obviously, orchard management practices that can create a warmer orchard environment during these low temperature events has the potential to significantly reduce losses.

Dormant Bud Stage Bud Swell Stage
Dormant Bud Stage - outer buds (left and right) are flowers.  Inner (middle) bud is vegetative and will develop into a growing shoot.  The dormant flower buds have yet to expand - bud scales are still intact.  In northern climates, deep winter cold injury can occur to dormant flower buds but this condition is rare in southern climates.  This is the most cold-resistant stage.
Bud Swell Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 18 F and 1 F, respectively.
Green Calyx Stage Red Calyx Stage
Green Calyx Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 21 F and 5 F, respectively.

Red Calyx Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 23 F and 9 F, respectively.
First Pink Stage First Bloom Stage
First Pink Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 25 F and 15 F, respectively.
First Bloom Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 26 F and 21 F, respectively.
Full Bloom Stage Post Bloom Stage
Full Bloom Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 27 F and 24 F, respectively. Post Bloom Stage -  According to the WSU Bulletin 0914 noted above for ‘Elberta’, the average temperatures required to cause 10% and 90% kill at this bud development stage were 28 F and 25 F, respectively.  This is the least cold-resistant stage.

 

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