tt-158 BY DON MEEHAN

SERIES ON WINTER INJURY OF LANDSCAPE PLANTS - Part 3 - Symptoms of Injury

Plants in the Pacific Northwest may suffer injury due to extremely cold temperatures or other types of winter weather. These past few winters have been especially severe. This column will be devoted to a four-part series on winter injury of landscape plants. The first parts covered "How Winter Injury Occurs" and "Types of Winter Injury". Today's column is Part 3 of the series.

PART 3: SYMPTOMS OF WINTER INJURY

The symptoms of winter cold temperature injury will vary depending on the plant species in combination with the condition of the plant and factors that cause the injury. Cold temperature can result in a change of color of the leaf tissue, including reddening, yellowing, browning or blackening. Yellowing (chlorosis): Production of chlorophyll, the green pigment in plants, ceases with cold weather. This allows the always present yellow pigments to become visible. Yellowing may progress to browning. Browning or Blackening (necrosis): Browning or blackening of the leaves results when tissues are killed or damaged. Severely damaged tissue may become glassy-green and later turn black and slimy or crispy. Reddening: Purple or red leaves or spots on leaves is a normal occurrence in the winter. Production of chlorophyll ceases and production of the red plant pigment increases. Red leaves or spots may be triggered by cold or even day length. Plants recover in the spring and return to healthy green. This is commonly seen in between veins of ivy, Oregon grape leaves, and spots on rhododendron and salal leaves. Delayed Symptoms: The results of winter injury can sometimes take months or years to appear. Sometimes the leaves can live on their reserves until they are depleted. This occurs slowly in cool weather or rapidly when the weather becomes suddenly hot. Cold temperature injury may damage tender stem tips which form next year's buds early in the spring of the current year. Thus the effects of the damage may not become evident until a year later when poor flowering and growth is noted. Graft unions are sensitive to damage from cold winter temperatures. Only a portion of the graft may be injured. It may function for years until another kind of stress causes it to fail. Winter-damaged tissue may allow the penetration of disease organisms. Winter-damaged trees are also more susceptible to insect attack, especially borers. Root systems, especially shallow ones, may be injured by cold winter temperatures. The damaged root systems fail to function adequately and the top of the plant may thin and die back. How You Can Tell if a Tree or Branch is Alive: Check it out. Before pruning a sad looking plant to almost nothing or pulling it out altogether, check to see if it is still alive. Scrape the bark away with a fingernail or make a shallow slant cut just under the bark with a pocket knife. Live branches are bright green just beneath the bark. Dying branches show fading green. Dead branches are brown and may even be soggy. Check the tree or shrub in several places; at the twigs; down the branches; and the crown or soil line. If the outer twigs have died, keep moving towards the trunk until you hit live tissues; older wood may be more hardy than younger wood. Sometimes the faded green branches may begin to regrow and do not die. Removal of damaged tissue should be done after the plant has been given a chance to recover. Part 4 of the series will cover what to do for winter-injured plants. Don Meehan is on the faculty at Washington State University working in Island County as a County Extension Agent. He is located at the Coupeville WSU Extension Education Center. The phone number is 679-7327. Cooperative Extension programs are available to all without discrimination. This information has been provided by Sharon J. Collman, WSU County Extension Agent, and Ray Maleike, WSU Extension Horticulturist.




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