Frost damage in apple and sweet cherry

The weather forecasting predicted below freezing temperatures this past Friday (April 2nd) and this morning (Saturday, April 3rd) in the Winchester area (22602). The temperature data as it appears now on the weather network show 2h of 29 oF on Friday morning, 3h at 26 oF and 1h at 25 oF this morning. All these temperatures are above the threshold that causes 90%-kill for flower buds, but can certainly result in 10% damage for apples, sweet cherries, and peaches. To get a better idea of how much damage has occurred after the Friday frost, my research team and I collected flowers from two apple cultivars, a peach cultivar, and a cherry cultivar and evaluated flower viability after 9h of frost (around 3:00 pm, yesterday/Friday). Unfortunately, our data showed 46% and 56% mortality rate in Pink Lady apple and ‘Ebony Pearl’ sweet cherry, respectively. We observed 0% damage in the flowers of ‘Honeycrisp’ apple and ‘Sunhigh’ peach. It’s worth noting that the 46% damage observed in ‘Pink Lady’ flowers is from the King flowers only. We haven’t examined any of the side flowers because they were relatively smaller and hard to observe. It’s also important to know that ‘Pink Lady’ is at the ‘first pink’ stage now, whereas ‘Honeycrisp’, like most of our apple cultivars, are still in the ‘tight cluster’ stage. The majority of our sweet cherry and peach cultivars are at the ‘white bud’ and ‘Pink’ stage, respectively. We will examine these cultivars again tomorrow, Sunday, April 4th, to determine the final percentage of damage after the two frost events. Knowing this information is crucial before starting blossom and fruit thinning. Below are some images to show the extent of frost damage in different species. 

We used a sharp razor blade to prepare longitudinal sections of sweet cherry flowers at the ‘white bud’ stage. Notice the green style and ovary tissues in the middle, as indications of flower viability. We assessed the damage for 30 flowers collected from different branches and trees.
Longitudinal sections of ‘Pink Lady’ apple flowers at the ‘first pink’ stage. More than 30 king blooms were assessed for damage after 9h of a frost event that occurred on Friday, April 2, 2021 in Winchester, VA.
Longitudinal sections of ‘Ebony Pearl’ sweet cherry flowers at the ‘white bud’ stage. Blossoms were assessed for damage after 9h of a frost event that occurred on Friday, April 2, 2021 in Winchester, VA.
Longitudinal sections of ‘Sunhigh’ peach flowers at the ‘Pink’ stage showing alive flower styles and ovaries after a frost event that occurred on April 2nd, 2021.

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