Leaf Scorch, Already!
Posted: July 25, 2009
One would assume that with all of the moisture that we have received that plants would not have much trouble this summer. Unfortunately, with all of the extra plant growth, scorching of the plants leaves was going to happen as soon as it warmed up. Simply put, just too much foliage for the plant’s root system to handle.
Dehydration of leaf or branch tissue occurs when more water is lost through leaves than can be replaced through the roots. Environmental factors include fluctuating temperatures, intense heat too early in the season, poor root development due to cold soil, prolonged dry summer weather; dry winters; low relative humidity; wind; soil with high salt concentrations; and restricted root growth from too much water and compacted soil. Other factors that induce injury are new construction near the tree (sidewalks, driveways, buildings); landscaping practices that use plastic as weed barriers; and soil grade changes.
Leaf scorch appears as areas of discolored tissue between leaf veins or along leaf margins. These irregularly shaped, discolored areas can be light tan to dark brown. Winter freezing of deciduous tree roots can result in leaf scorch the following summer. A late freeze can also cause tissue damage.
Leaf scorch is most severe on the side exposed to the contributing factor. For example, hot, dry winds cause most symptoms to appear on the side exposed to prevailing winds. However, in some cases, heat reflected from white or light colored siding can cause scorch, especially to conifers, even on the north side of trees. In advanced cases the entire tree appears dry and scorched. Severe scorch can result in complete defoliation because leaves dry up and fall prematurely. Trees defoliated before midsummer often form new leaves. Those defoliated in late summer may not grow new leaves until the following spring.
Scorching can also occur in evergreens due to drought conditions of past seasons. This type of damage can include tip dieback of needles, progressing from the tree’s top downward and from outer branches inward. A severe case appears as a sudden browning of all needles. Browning and dehydration of older needles (those nearest the tree’s interior) most often is caused by a chronic drought problem but can be from natural needle drop.
Do not overwater trees and avoid polyethylene plastic under mulches. Use porous weed control fabrics instead. Polyethylene plastics and overwatering contribute to oxygen starvation that results in root death. A gradual yellowing of foliage that develops first on the tree’s interior and progresses outward indicates oxygen starvation. Root waterers can help airate soils by opening up tight soils and provide drainage holes
Source: CSU Fact Sheet no. 2.932, Environmental Disorders of Woody Plants by C.E. Swift, W.R. Jacobi, M. Schomaker and D.A. Leatherman.