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Tree Fruit: What are chill hours?

Mississippi's winter chilling information

Deciduous fruits and nuts stop growing in late summer or fall, drop their leaves, go dormant during the winter, and then resume growth in the spring. This relationship between plant and environment is important to the survival of the plant. Growing plants that are non-hardy and incapable of becoming hardy need dormancy during winter for survival. In areas where winters may fluctuate between cold and mild temperatures, species have developed long chilling requirements, so they will not begin to grow in midwinter even though it may warm up to growing temperatures for several days.

Endodormancy (rest) is defined as that period when buds are dormant because of internal physiological blocks that prevent growth even under ideal external conditions for growth. Chilling termperatures above freezing terminate endodormancy. Chilling hours are defined as period of time between 32º F and 45º F. Plants are assigned a certain chilling requirement based on the amount of cold needed to cause 50 percent of the buds to break and flower in the spring. Most blueberries have a chilling requirement of 400-600 hours. Peaches are planted using the chilling requirement as a criteria for variety selection and range from a low of 400 to a high of 1250. Average chilling hours during the winter in Mississippi are: Hattisburg - 400-600; Jackson - 600-800; Mississippi State University - 800-1000; and Holly Springs - 1000-1200.

In 1999, middle to lower Mississippi experienced a low chilling hour accumulation. There is a material (Dormex) that can be sprayed on the commercial plantings that will substitute for about 200 hours. This material is a restricted-use pesticide and can damage the plant if used improperly. Dr. John Braswell, Dr. Frank Matta, and I have asked for, and received, a Mississippi Label for this material.

Dr. Arlie Powell (fruit specialist in Alabama) has performed research and demonstrations with Dormex in Alabama for over 10 years. Information concerning Dormex can be found on their web site, Alabama Winter Chilling

At this time, we feel that we will accumulate sufficient chilling hours in Mississippi. However, some growers may be interested in discussing the use of Dormex in late Febuary.

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Publications

News

Two rows of trees extend into the distance.
Filed Under: Commercial Fruit and Nuts, Nuts November 11, 2022

Mississippi pecan producers faced a particularly challenging year with drought and then rain at the wrong time, but irrigated orchards are making a good crop.

Eric Stafne, fruit and nut crop specialist with the Mississippi State University Extension Service, said the dry summer did one very good thing: It helped control pecan scab, a disease that is often a problem for the state’s pecan trees.

Filed Under: Agriculture, Crops, Commercial Horticulture, Commercial Fruit and Nuts July 27, 2022

CARRIERE, Miss. -- Individuals interested in muscadine production can attend an upcoming field day dedicated to the fruit. The 2022 Muscadine Field Day will be held Aug. 25 at the Mississippi State University McNeill Research Unit.

Filed Under: Agriculture, Commercial Horticulture, Commercial Fruit and Nuts, Other Vegetables, Livestock, Beef, Beekeeping, Goats and Sheep, Poultry, Forestry, Marine Resources April 14, 2022

RAYMOND, Miss. -- Agricultural producers and industry professionals met with Mississippi State University personnel in the coastal region to discuss research and education priorities at the 2022 Producer Advisory Council meeting. The annual event aims to help clients improve their productivity. Attendees gathered in small commodity groups at each event to share their ideas with agents, researchers and specialists with the MSU Extension Service and the Mississippi Agricultural and Forestry Experiment Station.

Filed Under: Agriculture, Commercial Fruit and Nuts, Fruit, Beef, Beekeeping, Equine, Goats and Sheep, Vegetable Gardens, Forestry, Wildlife March 4, 2022

Central Mississippi agricultural producers and industry professionals met with Mississippi State University personnel to discuss research and education priorities at the 2022 Producer Advisory Council meeting on Feb. 23 in Raymond. The annual event is aimed at helping clients improve their productivity. Attendees gathered in small commodity groups to share their ideas with agents, researchers and specialists with the MSU Extension Service and the Mississippi Agricultural and Forestry Experiment Station.

Blueberries grow on a bush.
Filed Under: Commercial Fruit and Nuts, Fruit January 14, 2022

STARKVILLE, Miss. -- Blueberry growers and those interested in entering this industry can participate in an online Mississippi State University workshop Jan. 27.

Register for this MSU Extension Service workshop by Jan. 26 at . There is no cost to attend the online workshop, which runs from 2-4 p.m. Jan. 27.

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Portrait of Dr. Eric Thomas Stafne
Extension/Research Professor
Fruit Crops