There have been many cases of leaf scorch in Illinois the past week. This disease is a noninfectious, environmental scorch that occurs each year when water cannot be translocated to the foliage as rapidly as it is lost. The causes vary and might include root injury, root rot, poor soil conditions, high winds, transplant shock, flooding, drought, and so forth. The possibilities are explained more completely in Report on Plant Disease No. 520.
Symptoms of scorch include browning of the leaf margins as well as tissues between veins. If you have been inspecting trees regularly, you may notice that injury appears first on the newest, most tender growth with the thin cuticle tissue. If you have not been as diligent, you may not notice anything until the entire tree is affected. Often, injury is worse on the south and west sides of the tree that are more exposed to wind and sun. Badly affected leaves drop from the tree, but most scorched leaves hang on and become tattered and torn as the wind whips the scorched areas.
Scorch does not kill a tree. To assess the tree’s ability to refoliate, look for live buds on the twigs. A bud is alive if it is green and fresh inside. Pick off a few buds and look at their base to make this observation. Also, try scraping the newest twig growth with your thumbnail. If the wood is green and fresh when scratched, it has a good chance of producing more leaves. If there are no live buds and internal wood tissue is dead, then a more serious problem has affected your tree.
Trees scorched due to weather stress just need a little extra TLC. Water them in periods of low rainfall and consider applying a balanced fertilizer in the fall. Remove any dead wood that may be visible in the trees. Otherwise, turn your attention to other areas of the garden.