Fruit, veg growers have options to protect crops
April 11, 2012 By Ohio State University
April 5, 2012, Piketon, OH – An extended period of unseasonably warm weather in March that led to vegetation reaching growing stages more than a month earlier than normal has left many fruit and vegetable growers considering contingency plans to protect their crops in the event of a frost or freeze.
From row covers to wind turbines, growers are weighing their options considering they still have several weeks to deal with the potential of a frost or freeze event, said Brad Bergefurd, an Ohio State University (OSU) Extension horticulture specialist.
Fruit crops are in various stages of bloom and freezing temperatures are a concern, he said, noting the temperature at which fruit buds are injured depends primarily on their stage of development.
“One really cold night could do many growers in,” Bergefurd said. “A lot of fruit growers aren’t sleeping well and are a little edgy until we get through April and through the bloom period.
“Being as far advanced as we are now in the growing stages, the potential for freeze injury exists, which could result in misshapen fruit or low-quality fruit or the total death of the blossom. You can get frost or freeze injury at 33 (Fahrenheit).”
As flowers swell and expand into blossoms, they become less resistant to freeze injury, he said. Not all blossoms on a tree are equally tender. Resistance to freeze injury varies with plant types as it does between orchards, fruit crops and cultivars. Buds that develop slowly tend to be more resistant.
As a result, some buds can be killed at higher temperatures, while others are resistant at much lower temperatures, Bergefurd said.
The financial impact for growers could be devastating, Bergefurd said.
“We could lose an entire crop or have a reduced crop load depending on when or if a frost or freeze happens,” he said.
But there are measures growers can take to protect their crops from frost or freeze, including:
- Sprinkler Irrigation – Growers can use sprinklers to prevent freezing injury by using the energy that water releases when it freezes and changes from a liquid to a solid, to keep the temperature in the ice right at the freezing point. As long as growers keep the ice wet, the ice temperature will stay around freezing. If the ice dries out and water starts to evaporate from the ice, the ice will get colder than the air temperature as it evaporates.
- Row Covers – Growers can use row covers as a protective covering to shield plants from the effects of cold and wind. The covers can add an extra five to 10 degrees of warmth under the blanket to keep frost off tender blooms or blossoms.
- Tractor-mounted Frost Control Machines – Growers can mount large fans with propane heaters onto tractors and drive throughout the orchard to circulate warm air through the orchard by blowing streams of hot air to both sides which are aerodynamically clean, without turbulence so they penetrate the cold air mass, forming a warm air layer at the height of the trees or crops
- Wind Machines – Growers can use wind turbines with 20-foot propeller blades stationed throughout the orchard to circulate air and raise the temperature in orchards by circulating warmer air down to crop level through the orchard.
- Fog – Growers can create fog using a smudge pot as a frost-protection method. The idea is to duplicate the greenhouse effect, using a “cloud” to blanket the crop area to decrease radiative cooling and stop the plant from dropping to the critical temperature.
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