We collected some information regarding apple frost damage during harvest and here is what we found.
Dr. J. Shupp, Professor of Pomology at Pennsylvania State University advises on how to handle frozen apples during harvest. He indicates that “apple fruit can withstand up to 4 hours at 28°F before injury occurs”, and the rate of thawing will affect the recovery. However, there are differences between varieties, probably due to differences in sugar content and maturity. More information can be found at https://extension.psu.edu/fruit-harvest-handling-of-frozen-apples.
Dennis M from Minnesota Extension answered the question, How cold can it get before apples are harmed on the tree?. In summary, he recommends waiting until the frost has left before starting harvest. Fruit can better resist low temperatures on the tree than in a bin. The freezing point of apples is approximately 29°F, but fruit needs to be exposed for a long period at that temperature to freeze. For more information, review the link above or click here.
Kathy Wiederholt from North Dakota State University shared similar information in the article “When to harvest apples”. Temperatures below 28°F can generate ice crystals inside the cells and produce damage. She added that if the days are cold and cloudy prior to the freeze event, the fruit will freeze faster than if the day had been warm and sunny. Reiterating to not touch the fruit until they thaw, and to not consider long storage.
In the article Doesn’t the cold just frost your apples? from Michigan State University Extension a light frost is consider to be when temperatures are between 28°F to 32°F and it should not affect the fruit. However, if there are several nights with temperatures around 28°F there could be fruit drop. They consider a hard frost when temperatures are below 24°F, even if it is for one night. The authors indicates that a hard frost induces the production of ethylene leading to abscission. Management practices can minimize the drop with the use of plant growth regulators.
- Fruit damage can occur with temperatures below 28°F for more than 4 hours.
- Do not manipulate frozen fruit; wait until fruit are completely thawed.
- Fruit can recover from mild freezing.
- If frost damage is suspected, do not consider for long term storage, and monitor firmness.
- Indicators of irreversible frost damage are: flesh browning, softens faster during storage.