Plant Pathology Infobytes
July 19, 1996
Tree Leaf Scorch Due To Weather Stress
County Extension offices across the state have been asked the following type question numerous times over the past few weeks: The leaves of my maple tree are turning brown along the margins then dropping from the tree. What's causing this?
While there are several possible causes for this problem, the most likely answer is leaf scorch, which has affected not only maples but other popular landscape trees such as dogwoods, Bradford pears, sycamores, and some evergreen species.
Leaf scorch typically appears following periods of extended dry, hot weather and occurs because tree roots are unable to adequately supply leaves with water. When water is lost from leaves faster than it can be replaced from the soil, leaves become dry and scorched. It's not unusual for scorch damaged leaves to drop from trees.
Although many areas of the state recently received rainfall, it wasn't in time to prevent the leaf scorch symptoms which are now showing up on maples and other trees.
Dogwoods, due to their shallow root system, seem to be more adversely affected by hot, dry weather than most other tree species. Dogwoods in home landscapes, and in woodland settings, typically show severe marginal leaf scorch following dry condi- tions, but also may show wilt symptoms. Frequently, drought- affected dogwoods have upper branches with light to deep red leaves.
Dogwoods and other young trees transplanted within the past few years are especially vulnerable to weather stress injury and should be watered with 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.
Mulch around trees to conserve soil moisture and prevent injury to the bark from lawn mowers or string trimmers.
Trees growing in compacted soils or sandy soils that don't retain moisture well are also vulnerable to weather stress, as are trees with root problems resulting from construction injury, pavement over roots, or other problems.
Remember, trees in the landscape mean added value. Keep an eye on your investment.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.