A serious problem that has appeared this summer and fall in various trees in our area is caused by an unfavorable environment. There is no chemical control, so the most effective defense against this problem is good management.
The culprit is leaf scorch. It is often called a disease, but is not caused by fungus, bacteria or virus, nor from insects; however, these problems can ad to the seriousness of scorch.
Trees most likely to be affected by leaf scorch are sugar maple, Norway maple, beech, horse chestnut, ash, oak and linden, as well as Japanese maple and dogwood growing in
full sun, although the problem can appear on almost any tree if weather conditions are unfavorable--such as prolonged high temperatures, dry winds and low soil moisture--which is the case this summer and fall.Even broadleaf evergreens may show leaf scorch, not only in summer, but in winter. Plants of this type most likely to scorch are rhododendron, azalea, laurel and Japanese andromeda. Narrowleaf evergreens are also susceptible, and those most frequently affected are pine, hemlock and spruce.
Leaf scorch symptoms on trees commonly appear as yellowing between veins or along margins of leaves. The yellowing becomes increasingly severe and the tissue dies, becoming brown, and this is the stage at which the injury becomes most noticeable. Winter leaf scorch in plants such as rhododendron usually appears as two long, brown areas paralleling the main leaf vein. Narrowleaf evergreens show leaf scorch as browning of needle tips.
Symptoms usually appear after drying winds and periods of hot, dry weather, although it can suddenly appear when long periods of wet, cloudy weather are followed abruptly by windy and sunny weather.
Leaf scorch is caused mainly by hot, dry weather where leaves do not receive ample water. Other conditions that can contribute to scorch include shallow soils overlying rocks or hardpan, poor heavy soils that do not retain water, damaged root systems, plantings near concrete and asphalt
that prevent water from getting to root systems.When leaf scorch is noticed, leaf tissue has dried beyond point of recovery, but steps can be taken to prevent more severe damage and improve conditions in subsequent years.
Most important is thorough, deep watering of affected plants. Some other suggestions are: In spring apply a complete fertilizer high in potash and containing minor elements, but don't fertilize after June to prevent young, soft growth of leaves which will scorch easily in hot summer winds. Also, avoid fertilizing with excessive nitrogen fertilizer. Establish a good insect and disease control program. Insect and disease damage can reduce tree vigor and encourage leaf scorch.Conserve soil moisture by mulching trees and shrubs with rotted leaves, bark or other material, and be sure to water
thoroughly when necessary because the mulch will absorb some of the moisture.If roots have been damaged from transplanting, grading, etc., prune back tops of plants to balance the reduced root system.
Of course, deciduous trees and shrubs will soon be losing their leaves because of the season, but if you have noticed leaf scorch, you need to water affected plants thoroughly so that they will have sufficient moisture during
dormancy, otherwise, they may not survive.University of Missouri Extension Bulletin G6881 offers more information on leaf scorch.