Flower bud hardiness in fruit crops

by George Hamilton, Field Specialist in Vegetable & Fruit Production, Hillsborough County.

Winter of 2015-2016 might be the mildest winter we have seen except for two events. On February 14 and 15 we had record low temperatures of -8 F to -15 F degrees or lower in some regions. We know that peach buds were affected by this cold weather event.

The temperature at which fruit buds are injured depends on their stage of development. As flowers begin to swell and expand into blossoms, they become less resistant to freeze injury.

With the warm temperature in March through April 2, we saw rapid fruit bud development. In southern New Hampshire some apple varieties had buds that were at silver tip to green tip stage of development. The cold weather that occurred on April 4, 5 and 6 could have caused some damage to apple buds, but not likely enough to reduce crop load. Damage will show up during the later stages when dead flowers fail to expand as the rest of the bud leafs out. We just have to wait and see.

Remember that not all buds on a tree or plant are equally susceptible to a particular temperature. Those that are farther along will be the most susceptible. Also, it has been cool, or down right cold, for the past week which has helped the buds to acclimate giving them even a degree or so additional hardiness.

This PennState Extension table 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.

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