Green Industry Resources
Hort Update- Seasonal Information for the Green Industry
Prevent Leaf Scorch in Trees with Deep Soaking
Leaf scorch is a water-related stress that is very evident on many Nebraska trees from mid to late summer. Symptoms of leaf scorch include a uniform yellowing or browning around the edges of leaves on broadleaf plants. If dry conditions continue the scorch continues into the leaf, resulting in dead tissue between the leaf veins. Evergreen needles turn brown uniformly, beginning at the tip. Spruce needles may redden, especially in areas facing south and the upper side of branches.
Gradually the symptoms spread inward resulting in scorched leaves that often fall from the tree early. This problem occurs most commonly on linden, maple, ash and cottonwood, but can be seen on other trees, too. The problem usually is more severe on the south or southwest side of the tree or on the side nearest a source of radiated heat, such as a brick wall or street. Severe scorch can result in premature leaf or needle loss.
Leaf scorch is caused by prolonged dry periods accompanied by hot, dry winds that create a water imbalance in trees as moisture is lost through transpiration faster than the roots can supply it to the leaves. Transpiration is the process of water evaporation from tiny openings in the leaf surface that cools and maintains leaf temperature. When water is lost faster than it can be replaced, the results are drying out and death of leaves and sometimes branch tips. Trees and shrubs are especially prone to leaf scorch in the first 2 to 3 years after transplanting while their root system is reestablishing.
Scorch problems can be reduced by regular watering during prolonged dry periods or by removing competing grass or other vegetation around the base of the tree and replacing it with an organic mulch, like wood chips. How much water should a full size, mature tree receive? This is a difficult question to answer because it is affected by many variables; like soil type, tree type, size of tree, topography of the land, etc. In general, trees need at least one inch of water each week; trees planted in sandy soils will need more. A majority of tree roots are located in the top 12" of soil, so watering with a root feeder often places the water below where it is needed. Instead use a small sprinkler running at a low rate, soaker hose, or just a slowly trickling hosepipe and let the water run for several hours to deeply water the tree. Water the entire area underneath the tree's drip-line in possible.