Each spring, we see many tree samples with blackened, tattered leaf edges. In most cases, the client wants to know whether the problem is infectious and if there is a control. This year is no exception. A few of the likely causes of symptoms include anthracnose, leaf scorch, leaf tatters, herbicide drift, and frost injury.
Anthracnose is a fungal leaf disease that appears in cool, wet spring weather. The fungi involved grow well in cool, wet conditions, while tree growth is slowed. Tender new leaves are most susceptible, thus the problem in spring. In Illinois, we see this disease most frequently on ash, oak, maple, and sycamore. Anthracnose fungi cause leaf spotting and blighting soon after leaf emergence. Sudden shedding of leaves may occur, which causes great concern to the homeowner. If you look closely at the affected leaves, spots are scattered, sometimes on the leaf edges and sometimes between or even on veins. Leaf drop and this scattered pattern can help in diagnosis. Although anthracnose looks ugly, it is not usually a growth problem to the tree. Affected leaves drop and the tree continues to produce new leaves. These emerge in warmer weather and usually escape infection. You can help by providing water and nutrients to help the tree refoliate. Refer to “Anthracnose Diseases of Shade Trees,” Report on Plant Disease, no. 621, for details about this disease.
Leaf scorch is an environmental condition caused by wind and heat desiccation of the tender new growth in the spring. This problem shows as a rather uniform edge burn to leaves, sometimes moving into interveinal areas of the leaves. Scorch is most intense on the south and west sides of the trees. The problem is prevalent in new plantings, heavy soils, or areas where water extremes are a problem. Rapid scorching may also cause blackened new growth. The new growth is most susceptible to injury as it has not yet developed a thickened cuticle that can help prevent drying. Injury to older leaves is less severe to nonexistent.
Leaf tatters occurs most frequently when scorched tissues are whipped around in strong spring winds. In recent years, tatters has also been used to refer to an unrelated problem on oaks (see issues no. 6, 1999; no. 7, 2003). As with anthracnose, usually trees with scorch or tatters recover with warmer temperatures and adequate water and fertilizer. New planting may be stunted for a while until roots are able to establish on the site. Refer to Report on Plant Disease, no. 620, “Leaf Scorch of Woody Plants,” for details about this condition.
Herbicide drift may cause injury to new growth of trees. Often the pattern of injury is most helpful in diagnosing herbicide drift and separating this injury from anthracnose, scorch, or tatters. Look at the potential source of chemical, the wind pattern over the past week, and the pattern of affected plants. If herbicides are to blame for tree injury, then other trees, shrubs, and bedding plants are affected in the path of the wind pattern. Damage is most intense on the exposed side of the plants and less so on the downwind side.
Frost or cold injury to trees and shrubs appears suddenly and occurs on succulent new growth more so than older growth. The affected tissue often turns gray–green, or it may quickly turn brown or black. Often the bottom growth escapes injury because heat is held by the plant canopy, while more exposed tissue is injured. Look at weather records to determine the possibility of frost injury. Hot days that promote succulent growth, followed by cold night temperatures can cause some cold injury.