Leaf scorch is a non-infectious condition caused by unfavorable environmental situations. It is not caused by any disease organism.
The problem may appear on almost any plant during weather conditions such as high temperatures, dry winds, and low soil moisture.
When large amounts of water evaporate from leaf surfaces and the plant roots are unable to furnish enough water to compensate for that loss, leaf tissue dies.
Young trees or those that are already in stress due to insect infestations, diseases, or other factors are more susceptible than those growing vigorously and in good condition.
Symptoms
Leaf scorch symptoms may differ from species to species. Symptoms commonly develop in July and August, when temperatures are high and rainfall is low.
Scorch affects the tips and edges of the leaves first. These leaf parts are the last to be supplied with water from the roots, so they are the first to be affected.
Scorch can begin as yellowing along leaf margins and tips. These tissues then become dry and brown if conditions do not improve.
Browning of dead tissue often appears without any previous yellowing if summer conditions are severe. Entire leaves may curl and wither during prolonged periods of heat and drought.
Scorched leaves may be more abundant on the side of the plant most exposed to prevailing winds, strong sunlight or sources of reflected heat, like brick walls or asphalt. Leaves on the same branch often show similar symptoms, but an entire plant may not be uniformly affected.
On needled evergreens, scorch injury begins from the needle tip progressing down toward the base of the needle. Scorch injury on evergreens may occur in winter from drying winds when soil is still frozen, as well as during warm, dry summers.
Causes
Symptoms of leaf scorch occur when one or more adverse factors are affecting the plant. In some cases, it is simply a sign that a particular plant is not suited to its exposure or the site in which it is growing.
Prolonged high temperatures, hot, drying winds, and low rainfall are the most common reasons for leaf scorch. Less obvious causes for scorch include roots that have been damaged from construction or recent transplanting, soil compaction, restricted root space, poor drainage, girdling roots, or high concentrations of de-icing salt, fertilizer, or chemicals.
Disease or insect damage to a plant’s root system may cause an imbalance of water between leaves and roots.
Wilt diseases, such as verticillium wilt, affect the water conducting vessels in the plant, restricting the water supply and creating conditions for scorch.
Management
Scorch damage alone is insufficient to kill an otherwise healthy plant. Proper treatment depends upon the reason for scorch symptoms; however, good cultural practices that improve general plant health and promote good root growth will reduce the chances of leaf scorch.
- When dry weather conditions occur over an extended period of time, plants should receive deep supplemental watering. Newly transplanted trees and shrubs are more susceptible to scorch, and their water supply should be monitored carefully. A slow soaking of the soil is most effective.
- Conserve soil moisture by mulching plants with a 3- to 4-inch depth of organic mulch, such as woodchips, leaf mold, or bark. Be sure to water thoroughly so water penetrates beyond the mulch and into the soil.
- Apply fertilizers in early spring or late fall, after leaf drop, to minimize the potential of root injury. Always water well. Avoid applying fertilizer to trees or to the surrounding lawn during the summer when soil is drier.