Take steps to protect your orchard trees from harsh winter weather.
When winter weather hits your farm, snow and ice can cause major problems for your orchard trees. Trees in northern areas tend to be especially winter hardy, but you should still take precautions to make sure your fruit crop returns during the growing season.
“The extreme-cold winter temperatures and high fluctuations between day and night temperatures may cause injury to fruit trees,” says Maurice Ogutu, a University of Illinois Extension horticulturist. “The flower buds, young shoots, tree trunks and roots of fruit trees can be killed by freezing temperatures. The plant tissues are injured more when there is an exceedingly fast drop in temperature at night during winter. The situation becomes worse when it is accompanied by strong winds. The damage is even more severe on frozen areas that thaw very fast.”
There are different types of winter freeze injuries that might occur underground and on the above-ground parts of fruit trees on farms and in home gardens:
Crown or Collar Injury
This occurs on the trunk near the ground surface and may extend a few inches below the soil surface, killing the bark of the tree and leading to reduction in surface area for movement of sap back to the roots
This occurs at the point where the branch joins the trunk. This could lead to the development of a canker on the affected areas and could require the branch to be pruned.
Leaf- and Flower-bud Injury
“The young shoots and twigs from the growth that occurred late in the season are not winter hardy and can be killed by severe winter temperatures,” Ogutu says. “The injury may also occur to leaf and flower buds.”
Trees extremely sensitive to cold temperatures could also completely lose their leaf and flower buds.
“The bud or shoot death can be minimized by not fertilizing fruit trees with high nitrogen fertilizers in late summer or early fall, and reducing or stopping irrigation in early fall,” he says. “It can also be minimized by growing fruit-tree varieties that are winter hardy and adapted to the area.”
The roots can also be killed by cold winter temperatures, particularly the roots that are closer to the soil surface. The symptoms of severe cases of root injury may be manifested on shoots and are mostly observed in midsummer.
“The fruit trees grafted on dwarfing rootstocks that are shallow-rooted need to be mulched in winter to protect roots from winter injury,” Ogutu says.
Winter Scald or Sunscald
This develops on the south or southwest sides of the tree trunk and lower branches due to rapid drop in temperatures on cold, sunny days in midwinter. The sunny side of the trunk thaws while the other side is still frozen, leading to cracking of the bark that may expose the woody part of the stem. The split area may develop into a wound that may turn into a canker that can kill the tree.
Sunscald can be managed by wrapping the tree trunks and lower branches on the southwest-facing side with burlap, aluminum foil, craft paper or special tree wraps. These are referred to as trunk guards. The trunk guards can be used in younger trees that have been in the garden for two or more years. A light-colored trunk guard will reflect sunlight during winter, thereby reducing the temperature on the bark. The trunk guards must be removed in early spring.
“White latex paint has also been used to protect fruit trees from sunscald for more than one winter,” Ogutu says. “White latex paint used for interior painting is much better than other types. Do not use oil-based paints, as they can injure the tree.”
Trees to be treated in this manner need to have been planted at least two years ago. They should be painted in late fall so that the paint can stay on the bark longer. Paint the trunks on sunny, warm days so the paint will dry quickly. In order to avoid tree injury, do not paint when the air temperature is below 50 degrees F. Apply the paint using a brush or other materials such as a sponge to get a thick coat that provides better protection.
“The whole trunk can be painted, although the southwest, west or south parts of the trunk may need more protection,” he says. “The parts of the trunk that need to be protected by the paint should be at least 18 inches above the ground and may extend into parts of the trunk above the lower limbs into the 10 to 12 inches from the base of each of the lower branches.”