The hot, dry days of July are more than a discomfort to many shade trees. Leaf scorch, which is a non-infectious disease is evident throughout the Midwest.
Leaf scorch is first noticed as a yellowing or bronzing of the tissue between the veins or along the margins of leaves. Trees are more susceptible if they have low vigor, have been damaged by machinery such as lawn mowers or trenchers or if surrounded by cement sidewalks and driveways.
The symptoms usually follow weather events of extended hot weather combined with drying winds. Later, the leaves appear dry and scorched, sometimes dropping off the tree. Another symptom to look for is the more or less uniform appearance of the leaves on a branch or side of the tree, where all or most of the leaves look dried and brown. It’s common for this to occur on the side of the tree that is exposed to prevailing winds or the west and south side sunshine.
At the heart of the malady, leaf scorch is the failure of the tree to supply enough water to the leaves of the tree at a critical time, usually in July and August when Mother Nature doesn’t provide adequate rainfall.
Trees with defective root systems are particularly subject to leaf scorch. The same holds true for trees surrounded by a substantial amount of impervious surfaces such as asphalt or concrete paving. Soil that drains excessively or is under attack by leaf sucking insects can also contribute to the scorch problem.
The good news about leaf scorch is that unless the tree is in its initial year, it will weaken the tree, but seldom kill it.
Leaf scorch cannot be corrected once it appears, but injury in following years can be kept to a minimum by improving the tree’s general condition. Here are some steps to take:
*Expand the mulch layer under the branches to reduce competition with turfgrass and weeds and keep the soil/roots moist. Pull the mulch back from the trunk 6 inches to avoid decay of the bark.
*Probe the soil under the tree’s branches and the adjacent landscape soil with a screwdriver to determine the moisture level. The goal is to keep the soil moist, not soggy or dry.
*Water the tree when the probe indicates dry soil. Soaker hoses and portable sprinkler heads can be used; even simply laying the hose end on the soil surface and letting water trickle out for an hour will do a good job of watering if moved to different parts of the root system each time you water.
*Avoid fertilization of the tree. Attempts to improve the tree’s health through fertilization are well-intentioned, but often encourage excessive leaf and stem growth, which makes future scorch worse. If the turfgrass near the tree is being regularly or even occasionally fertilized, the spillover is adequate for the tree.
*Inspect the tree weekly for symptoms of other maladies such as insect feeding and disease development. Hire an NAA or ISA certified arborist to assist you if you’re not sure of control measures to take. Obtain assistance here:
*Be patient with the time it takes to improve the tree’s health. It may take several years of following the steps above to reduce the incidence of leaf scorch.