Leaf Scorch of Trees and Shrubs

Leaf scorch is usually recognized as a necrosis of browning and death or leaf tissue which can occur around leaf margins or along interveinal areas (leaf area between veins). It can occur on almost any species of tree or shrub. Evergreen green trees and shrubs exhibit scorch as needle browning. Scorch can be related to one or more factors such as weather, growing site, injury to stem, insects or disease.

Symptoms

Scorch initially may appear as yellowing along leaf margins or interveinally. Later browning or bronzing of the affected leaf tissue occurs. In severe cases the entire leaf may brown, leaving only midribs green. Generally most of the leaves on a certain part of the plant or over the entire plant will be affected. Scorch symptoms would not normally occur on a few scattered leaves here and there.

Causal Agents

One or more of the following factors can be involved:

  1. weather — drought, dry winds, bright hot sunshine are the most common causes. Scorch ay also occur along damaged edges of wind battered leaves.
  2. factors restricting water uptake — girdling roots, root damage from nearby construction or soil disturbance, change in soil grade, change in water table, compacted soil, soil area too restricted for root growth, flooding or standing water resulting in smothering and death of roots, sandy soil.
  3. heavy infestations of sucking or boring insects, insect or rodent damage to roots.
  4. chemical or mechanical damage — toxic concentrations or incorrect application of deicing salt, fertilizer or pesticides, injury or wounds to bark on main stems or trunk.
  5. disease — wood rot, fungal cankers on affected branches or trunk, root disease, wilt disease, slime flux (wetwood).

Control

Check the list of causal agents and determine which one or ones could be causing the problem with your plant and take measures to correct the situation if possible.

  1. Water during periods of prolonged dry weather if possible. Large trees should be watered at or near the drip line of the tree since there are few feeder roots close to the trunk. Soil should be moist to a depth of 10 to 12 inches after the watering. Feeding lances which attach to garden hose are ideal for watering. Plants low in vigor or recently transplanted are most sensitive to lack of water and need the eqivalent of 1″ (2.5 cm) of rain per week.
  2. Check for signs of fungal canker or wood rot disease. Look for evidence of discolored, cracked or peeling bark. Remove diseased bark back to tissue you are certain is healthy and firmly attached. Disinfect the area with alcohol or household bleach (diluted 1 part bleach to 3 parts water) and treat the area with tree wound dressing. Mushrooms growing on trunk or branches indicate wood rot disease for which there is little taht can be done.
  3. When a wound or trunk damage is obvious, it should be cleaned and treated to prevent entry of disease organisms and promote healing.
  4. If plants are known to have suffered root damage from transplanting or construction or are known to have root growth restricted by barriers, prune the tops to reduce water loss and reduce the amount of water roots must take up. Keep such plants well watered.
  5. Loosen surface layers of soil where soil is heavy and compacted to allow better penetration of water and air to the root zone.
  6. If insects are known to be heaviliy infesting the plant determine what they are and apply insecticide accordingly. Be aware that come insects such as many types of wood borers are extremely difficult if not impossible to control. Pruning of affected parts or removal of infested plants may be the only measure available.
  7. When fertilizers, fungicides, or insecticides are applied read the label carefully for information regarding time or growth stage at which it can be applied, concentrations, temperature restrictions, etc..
  8. Protect thin barked trees (eg. fruit trees) from sunscald by shading trunk and large branches on south and southwest side during late winter and early spring. Diluted white or light colored latex pain (1 part paint: 10 parts water) could be applied to reflect the suns rays also.
  9. Fertilize at lease every few years to maintain vigor. Plants in poor soil would likely benefit from annual applications. Early spring is the best time to apply fertilizer for woody plants.