Thursday, November 15, 2007

Landscape - Winter Injury on Landscape Plants

With winter fast approaching, landscapers should take some time to familiarize themselves with winter injury symptoms on ornamental plants and plants that commonly show winter injury. The following is an article on this subject.

Winter injury is a result of many environmental factors. The causal factors are diverse and include late spring frost, a cool summer followed by a warm fall or a sudden drop in temperature, excessive or late season fertilization, excessive temperature fluctuations, abnormally cold temperatures during winter, drying winds, and lack of snow cover. Growing plants out of their hardiness zone reduces their ability to survive low temperatures during the winter.

Excessive drying (winter desiccation) is one type of winter injury. This is quite common in evergreens and occurs when water evaporates from leaves or needles on windy or warm sunny days during the winter or early spring. Drying occurs because this water is not replaced since the roots cannot take up enough water from cold or frozen soil. Winter desiccation is prevalent on broadleaved evergreens such as rhododendron and holly and on needled evergreens such as hemlock and pine. Rhododendron leaves affected by winter desiccation turn brown along the margins and roll longitudinally along the mid-vein. Desiccated needled evergreens exhibit browning of the tips of needles, needle drop, and twig dieback.

Periods of fluctuating winter temperatures combined with sunny calm days can cause sunscald (or sunscorch). Sunscald becomes evident when bark splitting occurs on stems or branches, most often on the southwest side of the tree. Other symptoms include dried buds, scorching or shriveling and dying of newly emerged foliage, twig dieback, scalding of bark, stunted annual twig development, and reduced plant growth. Smooth, thinbarked deciduous trees and shrubs are most prone to sun scald injury. Examples include flowering cheery and almond, Japanese and red maple, and flowering plum and peach.

Keep in mind that, unfortunately, symptoms of winter injury are not often evident until the following spring or summer. Winter injury will predispose plants to secondary infections by insects and diseases caused by living organisms.

Extracted from "Landscape and Ornamental Plant Stress: Factors, Symptoms, Diagnosis, and Management" by Gladis Zinati, Ph.D., Extension Specialist in Nursery Management, Ann Brooks Gould, Ph.D. Extension Specialist in Ornamental Plant Pathology, Richard Buckley, Coordinator Plant Diagnostic Laboratory, and Rich Obal, Monmouth County Agricultural Agent, Rutgers University.

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