Contact: Diane Relf, Extension Specialist, Environmental Horticulture
Posted April 1997
Leaf scorch is caused by the failure of the tree to supply a sufficient amount of water to the leaves at a critical time. An immense quantity of water is evaporated from the leaf surface during hot weather, especially by the drying action of the wind. If the water supply to the roots is deficient for any reason, the exposed leaves actually dry out and appear scorched. Trees with defective root systems are particularly subject to this problem, as are those whose roots have been partly removed or covered with impervious material such as asphalt or concrete pavement. Trees growing in poor soil where the drainage is excessive and the watertable low may show the disease only in unusually dry seasons. Attacks of aphids or other sucking insects, which rob the tree of moisture, may also contribute to the problem.
Trees with affected leaves have a dry scorched appearance. The discoloration may be light or dark brown, depending on the kind of tree attacked. The pattern of scorch may be very irregular and involve a considerable portion of the leaf. The effect is usually first evident between the veins or along the margin of the leaf, and ordinarily all the leaves on a given branch are affected more or less uniformly. It frequently happens that only one side of a tree is affected and that side is the one most exposed to heat or to drying winds.
Anything which can be done to improve the general condition of the tree will serve to reduce or minimize the injury. In trees with permanently suppressed or injured root systems, it is advisable to prune some of the branches to maintain a more even balance between the top and roots. If this is done carefully and judiciously, it will not injure the appearance of the tree and may actually improve it. Do not top back or dehorn the tree. Fertilizers, particularly those containing high amounts of potash, are reported to reduce leaf scorch. Suitable insect control should also be undertaken, since this may contribute to the general vigor of the tree. In cases where severe and permanent injury to the root system exists, a recurrence of the problem may be expected during periods of extreme drought. Help the tree through these periods by watering, if possible.
(Prepared by Jennifer Shuster, Extension Technician, Consumer Horticulture, Virginia Tech, Blacksburg, VA 24061-0327, from Suffolk County, NY, Consumer Hort News, by Caroline Kiang. Reviewed by Mary Ann Hansen, Plant Pathology Department, Virginia Tech.)
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