Leaf scorch is a physiological disease of plants which occurs when the roots are unable to obtain sufficient water to supply the top of the plant. Leaf scorch occurs when plants are transpiring rapidly during periods of high temperatures with hot, dry winds or during droughts. Any plant may experience this, but symptoms are more commonly seen on broadleaf trees such as maple, ash, elm, chestnut, and poplar.
Leaf scorch (also known as marginal necrosis) is caused by lack of moisture and has been evident for the past few weeks on many landscape trees. Tissue usually starts dying at the leaf edges or between leaf veins when the plant transpires more water than it can take up. It is often seen on plants growing near hot, reflective surfaces or on exposed, windy sites. It is most severe toward the top and outer branches.
Symptoms may begin with yellowing along the margins or between veins of leaves, or you may simply notice dead, brown patches in these areas. Seriously affected trees will have many leaves scorched and brown with only small amounts of green tissue on the leaves. The whole tree may develop symptoms, but frequently only the leaves on one side or a few branches turn brown. The tree will not die from leaf scorch unless it is seriously deficient from water.
In Utah, symptoms usually begin to show up in July and August. Newly transplanted trees may also develop leaf scorch because they have not had time to establish a good root system. Trees with damaged roots (from construction, etc.) or growing in areas surrounded by pavement also have difficulty in obtaining sufficient water and leaf scorch is the result. Often, similar leaf symptoms can be caused by excess salts in the soil which are taken into the plant and moved out into the leaves. Overfertilization and leaching of road salt applied during the winter can make soils high in salts.
The symptoms of leaf scorch will not kill a plant, but the underlying causes should be addressed. The plant’s ability to rapidly translocate water has been compromised, and this could be caused by:
· Frequent, shallow watering that cause the soil surface to become compacted and sun baked, and results in slow death of feeder roots;
· Girdling roots around the trunk;
· Lack of watering after transplanting;
· Recent construction or digging that has killed a portion of the root system;
· Trunk injuries by lawn care equipment.
Multiple years of moisture-induced leaf scorch may cause the tree to show symptoms of dieback in the upper canopy. Suckering along the trunk and large branches are its last-ditch effort to survive.
The best control for leaf scorch is to prevent conditions which usually create scorch. Deep irrigation during periods of drought and/or high temperatures is essential, especially during windy periods. Keep trees vigorous with proper fertilization in spring or late fall, and prevent injury to the roots and trunks from construction, lawn mowers, or girdling roots. Removal of a few branches by judicious pruning will reduce the water demands and consequently reduce leaf scorch. Treat with iron to alleviate any iron deficiency.
Mulch under trees out to the tree canopy with two to three inches of well-composted organic matter, keeping the mulch away from the bark of the plant. Water with a slow soaking system such as drip irrigation or a soaker hose for long and deep watering every week or every other week during drought conditions. Water from sprinklers for the lawn is not sufficient. Water trees planted in the last three years every week, and trees planted up to six years ago every other week. If you have limited water, focus on your new plantings and woody plants first, garden beds next, and lawns last.