With yet another arctic blast that just came through, I thought it would be good to talk about critical temperatures for fruit buds and flowers. Coming off of unseasonably warm early February temperatures, this could be very important to this year’s fruit crop.
Most of our fruiting plants and trees require a certain amount of cold temperatures to produce good quality fruit. Once that requirement is met it takes a certain amount of heat units to initiate flowering. With temperatures well above average through the first of February trees and buds have definitely begun accumulating heat units. If you have looked at any of your fruit trees you are sure to notice that the flower buds are beginning to swell.
So, what do low 20’s, which we experienced last week, mean for these developing flowers? Different plants have different tolerances to cold, and different stages of growth are better at handling cold as well. So what are the critical temperatures for fruit crops that we like to grow?
For peaches a dormant bud can handle extremely cold temperatures. The swollen buds that we are seeing in most of our area can handle 18-21 degrees before buds are killed. As we begin to see a little pink the flower is more sensitive and can only handle 25 degrees. At full bloom and post bloom that critical temperature is 28 degrees. Those are the temperatures that we can expect to see 10% bud kill. The temperatures that would cause 90% bud kill are a bit lower, and the duration of the cold event also plays an important role in bud mortality. These same numbers can be used for plums.
For Strawberries the numbers are similar. Buds that have not yet emerged are hardy down into the low teens. As buds emerge they become more sensitive. Emerged buds can handle around 25 degrees and open flowers can handle 28 if the air is dry.
Blueberries can handle low 20’s as flowers begin to swell, and 26 degrees as the flowers are about to open. After flowers are open temperatures below 28 degrees, even for a few minutes can cause damage.
Pears have also begun to swell, but if the weather forecast is correct they should be ok. Dormant buds can handle 15 degrees. 20 degrees can injure buds as they begin to swell. And once you start seeing white flower parts 26 degrees can cause at least 10% mortality.
The stage of growth that most of our fruiting crops are at should help protect them from this latest cold weather, but we may see some injury in low chill crops and strawberries that have been pushed to be early. General Beauregard Lee predicted that we would have at least 6 more weeks of winter. I just wish we could do something about the trend of warm weather in February. This has become the norm and is one of the biggest factors reducing fruit production in Georgia over the last several seasons.
Contact your County Agent if you have questions or comments.
