Extension Educator, Horticulture
They suffer the slings and arrows of outrageous people with baseball bats, garage sale flyers, bicycle chains and the occasional misguided car. Trees are survivors. They are determined to live and even thrive under less than ideal conditions. Trees also have their share of infectious and non-infectious diseases.
Each year we see some spotting and browning of tree leaves. Some tree species are prone to the same problems just about every year. Sycamore (or maybe it should be "sickagain") suffer from the fungal disease anthracnose to some degree each year. Other trees such as ash, maple, oak, elm, and walnut can also get anthracnose.
Crabapples are commonly infected with the fungal leaf disease apple scab. Resistant cultivars are less likely to be infected, but some cultivars will have leaf spots and leaf drop every year we have a cool wet spring. Luckily anthracnose and apple scab are mainly leaf problems and the trees continue to thrive despite the infection. To protect trees against these diseases fungicide sprays would have to be applied multiple times in the spring before infection occurs. It is too late to spray for much benefit this year.
Our recent hot dry days can cause a non-infectious leaf disease called leaf scorch. It is first seen as a yellowing or bronzing between leaf veins or along the margins of leaves. Frequently the side of the tree exposed to drying winds will show the most damage. Later, these leaves appear dry and scorched, and they may eventually drop prematurely.
Trees are more susceptible to leaf scorch if they have low vigor or reduced root systems. Trees that have been recently transplanted, have experienced damaged roots or bark from construction machinery, or are surrounded by asphalt or concrete sidewalks, driveways or parking lots may quickly show leaf scorch. It often appears when an extended period of hot dry weather follows a cooler wet period which describes our weather this past June and July.
Typically with many infectious and non-infectious leaf problems the buds and branches will remain alive. Look for green and plump buds on the twigs. Also try scratching the twigs. It should look green and moist under the outer layer. If the buds and branches are dry and dead, the tree may have a more serious problem.
In determining the cause of a tree's leaf problems first discover the tree species which will help determine the common problems for that species.
Generally the best management option is to promote good tree health; water during drought periods, remove dead or dying branches and fertilize if necessary in fall. Apply 2 to 4 inches of wood chip mulch to the soil around a tree. Ideally it should extend to the dripline or outer branches of the tree. Do not pile mulch next to the tree trunk like a volcano.
In addition samples (with pictures if possible) can be mailed or taken to the U of I Plant Clinic 1401 West St. Mary's Road Urbana 61802 PH:217-333-0519 Check their website for proper packaging and fees. http://plantclinic.cropsci.illinois.edu/
In addition contact your local county U of I Extension office. http://web.extension.illinois.edu/state