Leaf Scorch

The damage caused by ice earlier this year is showing itself in new ways every day. Many calls have come into the office related to plants that were once shaded by some of the grand shade trees that did not survive the ice storm. What plants are affected, what is going on and how can you help?

The plants that are most quickly affected, or perhaps noticed more readily, are understory plants. Those plants that grow beneath a larger shade tree include dogwood, Japanese maple and hosta. Other plants that may show effects now or in the future are azalea or rhododendron.

Observed symptoms include yellowing and then browning along leaf margins. Some plants may show this damage just along the edge while others may have a significant amount of distressed tissue, 1 inch along the edge or more, with scorch symptoms. As the damage becomes more severe it may move between leaf veins and the tissue may be affected so quickly that it dies without yellowing.

This ‘scorching’ of leave tissue is caused by water loss from the leaf surface at a faster rate than the plant can absorb it through the roots. Water is moved through the plant by veins; areas that are furthest away from the veins like the leaf tips and edges of leaves most exposed to the elements will be affected first.

Scorch will appear after a sharp change in weather condition. For example, the weather has been mild this year with plenty of rain throughout the season. We have experienced 2 hot and dry weeks in June and similar conditions in August. The sudden loss of rain alone could trigger a ‘scorch’ reaction as the root mass on plants may not have developed as much because of the continued rain. The sudden increase of heat could also have worked alone to trigger these symptoms.

Conditions that can lead to leaf scorch include decrease in water, poor root development, windy conditions, hot and dry weather (especially above 90 degrees), a sudden change in weather patterns, drought, low humidity and dry winter winds later in the season. These conditions, coupled with the lack of shade, have contributed to the increase of leaf scorch on plants in our area.

What can be done? If the plants are small enough to transplant then consider moving them to a more favorable location. If relocation is not possible, they will continue to develop scorch each year until they are killed from poor health conditions. For larger plants you can mulch around them to prevent water loss in the soil, put up a wind barrier or add shade. Make sure that the plants receive proper water but do not overwater. An application of 1 inch of water per week is the standard amount that a plant will take up.

Above all, keep the plants healthy so that the stress caused by water is the only thing that will give you problems. Spray for anthracnose in the spring, before you see disease symptoms. Apply proper fertility in the spring and again in June to insure your plant maintains good health. Prevent damage to the roots and trunk from machinery or tools. Prune the canopy if roots are damaged to maintain a 50 to 50 ratio. Watch for borer damage and address it as soon as you see it.

Remember that leaf scorch is not a disease but a condition of the plants environment. Symptoms may appear on only once branch or on one side of the plant or on the entire plant. It depends on exposure and water uptake. Thorough, deep watering helps increase water uptake instead of short applications of water several times each week.

Helpful Publication: Starbuck, Chris and Laura Kabrick. Leaf Scorch of Ornamental Trees and Shrubs. Publication G6881, University of Missouri Extension. Rev December 2002; Leaf Scorch of Trees and Shrubs. BP-25-W Purdue University Cooperative Extension Service. Rev March 2002

The Extension office is located in Kennett, Missouri at 101 South Main Street (the old bank) on the 2^nd floor. Open Monday – Friday or you can call 573-888-4722 if you have a question. University of Missouri Extension programs are open to all.

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Sarah Denkler, Horticulture Educator
University of Missouri Extension
P.O. Box 160, Kennett, MO 63857
573-888-4722 Denklers@missouri.edu