Plant Pathology Infobytes
August 12, 1999
Trees and Weather-Related Stress
The effect of hot, dry weather is showing up on some landscape trees. Dogwoods, ornamental , species of pear, maples, oaks, and other popular urban landscape trees have been especially susceptible to this summer's hot, dry weather.
Most weather-stressed plants typically exhibit marginal leaf scorch and "flagging foliage." These symptoms are signals the plant isn't receiving an adequate amount of moisture. Scorch appears along leaf edges and occurs when water is lost from leaves more rapidly than it can be replaced from the soil. As a result of moisture stress, the leaves become dry and scorched. Scorch is more likely to occur when hot, dry winds accompany drought periods. Defoliation sometimes accompanies drought stress.
Shallow-rooted trees are especially sensitive to hot, dry weather. For example, dogwoods in home landscapes, and in woodland settings, typically show severe marginal leaf scorch and foliar wilt. Frequently, drought-affected dogwoods have upper branches with light to deep red leaves.
Young trees transplanted within the past few years are also vulnerable to environmental stress and should be watered the equivalent of a one inch rain per week. As a general rule, water each week it does not rain. Water deeply to encourage deeper root penetration. Don't wet the foliage, and water in the afternoon to give the surface of the soil time to dry during the afternoon. Also, mulch around trees to conserve soil moisture and prevent injury to the bark from lawn mowers or string trimmers.
Trees which have had roots cut or otherwise damaged from new home construction, driveway construction, removal or addition of soil to a tree's root system (only a few inches of soil addition or removal often causes severe root injury), soil compaction which prevents water movement into the tree's root zone, and other factors are often responsible for root damage. Such trees with damaged roots fall into a category which places them especially at risk to weather stress, since damaged roots aren't capable of picking up adequate amounts of soil moisture needed to satisfy the tree's water needs. So, it's a good idea to keep an eye on "at-risk" trees which may have been suffered recent root damage.
What type of symptoms should you look for? Trees with injured roots often exhibit larger areas of brown, dying foliage -- typically on one side of the tree (often the side where the root injury occurred). This type symptom is an indication of more significant injury, and in many instances, the tree will continue to decline and die unless the early symptoms are noticed and prompt action is taken to relieve the stress. Unfortunately, the early warnings are often overlooked, and when the damage is noticed, it's often too late to start a program of remedial action in an attempt to save the tree.
What type of remedial steps should be taken? Often tree watering and fertilization are the best course of action, but each tree situation needs to be evaluated, so contact your County Extension Office for information guides on tree fertilization and watering practices. Don't delay -- the life you save could be your tree's. Remember, trees in the landscape mean added property value, so keep an eye on your investment.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.