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Choose Tolerant Fruit Varieties
MISSISSIPPI STATE -- Most Mississippians have forgotten the bitter cold days of winter as temperatures continue to climb. But bare trees, bushes and vines will long remind fruit growers of the early March freeze that gripped the state.
Dr. Freddie Rasberry, extension fruit and nut specialist at Mississippi State University, said the state's fruit crops suffered major losses from the freeze.
"About 25 percent of the state's apple crop and up to 90 percent of the peach, plum and nectarine crops were lost to the hard freeze," Rasberry said. "Virtually all of the strawberry crop south of Meridian was wiped out and much of the blueberry crop in south Mississippi was lost."
Helping Mississippi fruit producers choose varieties less susceptible to freeze damage is one of the goals of Dr. Frank Matta, horticulturist and researcher with the Mississippi Agriculture and Forestry Experiment Station.
Matta has established a plant cold hardiness laboratory at MSU to identify the injury-causing temperature for various fruit trees, nut trees and ornamental plants.
The primary purpose of the research is to provide recommendations to growers on the species or cultivar selections best adapted to Mississippi's climate.
Part of that research involves freezing the individual parts of fruit-producing plants.
Matta and research assistants are freezing the individual parts of the blueberry flower. A blueberry flower consists of the corolla, the stigma, the style and the ovary.
"One of the most important things we discovered is that the individual components freeze at different temperatures," Matta said. "The corolla, or the petals, are the first to freeze, followed by the stigma and the style. The ovary is the last to go, and as long as the ovary is alive you're still in business."
The research indicated temperatures in the mid-20s kill the outer parts of a blueberry bloom, but the ovary survives temperatures down to about 22 degrees.
"Before this information was available, producers would look at freeze-damaged flowers and assume they had lost a blueberry crop," Matta said. "But our research shows not all freeze-damaged flowers are a total loss."
Among the rabbiteye blueberry varieties tested, Tifblue was hardier than Climax, but not hardier than Premier. Among the southern highbush cultivars, Cooper and Gulfport suffered less cold injury than O'Neal.
Matta explained that cold-hardiness research also has shown an application of gibberellic acid can help freeze-damaged blueberry plants set fruit as long as the ovary is undamaged.
Dr. John Braswell, extension horticulture specialist in Poplarville, said temperatures dropped so low during March that about 80 percent of the south Mississippi blueberry crop was lost.
"Temperatures dropped into the mid-teens all the way to the coast during the early March freeze," Braswell said. "That was well below normal for south Mississippi and low enough to kill all but about 15 to 20 percent of blueberry blooms."
Mississippi's apple crop was not as severely damaged by the extreme cold. Most damage was confined to early varieties already in bloom or in the bud-swell stage.
"Apples can be a successful crop in Mississippi because they are likely to suffer less damage from late freezes," Matta said.
Research at the Pontotoc branch experiment station has shown that cultivars from the Campbell and Mercier strains can be top-yielding varieties in north Mississippi.
"Royal Gala and Granny Smith also have proven to be excellent producers of high-quality apples in northern Mississippi," Matta said.
Other MAFES fruit research includes projects with blackberries, raspberries, peaches, plums, pears and nectarines.