Many woody plants were injured this past winter by low temperatures, a condition most refer to as winter kill. In some cases, entire plants were killed; in others, only branch tips or sections of the plant were affected. It seemed like a mild winter overall, so what was different this year? The temperatures in December reached 20 below in Champaign-Urbana and many parts of northern Illinois. More importantly, the temperature drop was sudden, injuring tissues that were still growing. Stressed plants are more susceptible to such injury, and often low temperatures are actually the last stress that pushes these plants past the point of no return.
Even if sudden temperature changes do not kill a plant, they may do enough damage to cause temporary plant stress. Then canker fungi often infect and spread into a tree or shrub. The canker fungi are in the environment but do not cause problems on healthy trees and shrubs. To avoid problems with cankers, dieback, and plant decline, prune out the dead areas as soon as possible. If the plants are under drought stress for as much as 2 weeks, be certain to provide supplemental water. New plantings need water more often, especially in very hot temperatures. Do a complete site inspection for other possible sources of stress, and alleviate these where possible. For more on canker diseases and possible sources of stress, see Report on Plant Disease no. 636, “Canker and Dieback Disease of Woody Plants,” available in your Extension office or on the Web at http://www.ag.uiuc.edu/~vista/horticul.htm.