Environmental Leaf Scorch

University of Rhode Island GreenShare Factsheets

Environmental Leaf Scorch

Symptoms of leaf scorch due to environmental causes include browning of the leaf margins and yellowing or darkening of tissues between the main leaf veins. As the condition progresses, entire leaves may dry up, turn brown and become brittle. Leaves sometimes wilt rapidly, usually remaining a pale green color even when dried out. Damage is usually more pronounced on the upper, windward or southern side of trees. Plants may lose many leaves prematurely during late summer and exhibit some twig dieback.

Leaf scorch can be caused by many adverse environmental conditions, including soil compaction, transplant shock, nutrient deficiency, drought, salt toxicity and herbicide injury. Leaf scorch is common in the Northeast due to cold soils and slow root growth. The loss of leaves is seldom immediately fatal, but conditions causing leaf scorch should be corrected if possible--over time, they can cause the decline or death of the tree or shrub. Plants under stress are subject to secondary problems such as attack by insects or diseases.

To help prevent leaf scorch, prune sprouts and diseased areas. Maintain vigor through proper watering and fertilizing. Water deeply to encourage deep root systems that enable trees to withstand environmental stress such as drought and winter desiccation. Check soil moisture at least 12 inches down--if it is rather dry, water trees slowly and deeply, allowing water to penetrate at least two feet. Deep-water the entire area under the canopy, one and one-half to three times farther than the branches--95% of the roots of most trees, including tall evergreens and large deciduous trees, is found in the top 18 inches of soil in this extended area. Sufficient moisture will help keep the trees vigorous enough to withstand pest attacks, as well as help prevent winter injury. It is very important to deep-water trees and shrubs at least twice a year, especially in areas where the water table is far below the soil surface or on sites exposed to wind; water every fall, after leaves turn autumn color but before the ground freezes (perhaps at the same time fall fertilizers are applied if needed), and again in spring as soon as the ground thaws to replenish dehydrated roots. Avoid frequent, light waterings as well as watering only at the base of the tree trunk. Trees suffering from drought can be selectively pruned to reduce transpiration (the loss of water due to evaporation through the leaves). Drought occurs when transpiration exceeds the plant's ability to supply water through the roots.

To determine if trees need fertilizing, have the soil tested and supply any missing nutrients. Refer to the GreenShare Factsheet on soil testing for information on how to prepare soil samples. Avoid overfertilization, which can harm trees and ornamentals. Refrain from fertilizing unless soil tests indicate a specific necessity, or unless trees demonstrate symptoms of nutrient deficience--chlorosis, stunted growth or deformed foliage. Compacted soil can be loosened over time by the annual use of core aerators, which remove a plug of soil up to four inches long. Add an inch of finished compost to the hole--the compost will soon work its way down into the soil, loosening it over time. Using dark-colored permanent mulches under the entire canopy area can help prevent compaction once soil is loosened, and help warm soils at the same time.

When using herbicides near trees, do not allow mist to settle onto trees and avoid spraying branches, foliage or trunks with the solution. Apply pesticides only on windless days to avoid problems with drift.

Adapted from Sherry Lajeunesse, Montana State University, 2000

Pesticides are poisonous! Read and follow all safety precautions on labels. Handle carefully and store in original containers out of reach of children, pets or livestock. Dispose of empty containers immediately, in a safe manner and place. Pesticides should never be stored with foods or in areas where people eat.

When trade names are used for identification, no product endorsement is implied, nor is discrimination intended against similar materials. Be sure that the pesticide you intend to use is registered for the state of use.

The user of this information assumes all risk for personal injury or property damage.

For more information, call the URI CE Gardening and Food Safety Hotline at 1-800-448-1011 or (401)874-2929 from outside Rhode Island; Monday-Thursday between 9 am and 2 pm.

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