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Oak Leaf Skeletonizing

May 24, 2000

This problem has occurred in past years and is now present in parts of Illinois. We have reports from west-central, northern, and east-central parts of the state, and the clinic has received samples from the Champaign area. I have seen the problem on oaks, particularly those in the white oak family. The symptoms are quite bizarre. Much of the leaf is just gone. The tissue that remains is the vein tissue and a bit of leaf blade around the veins. Leaves appear to have been eaten by a voracious insect that prefers nonvein tissues. The edges of the leaf that remain are often brown or thickened like a callous tissue. Some refer to this as oak tatters. Others call it bare bones or oak skeletonizing.

What is the cause of this condition? We donít know for certain, but it appears to be the result of cold injury when the leaves were still in the bud. Look closely at the leaves. The injury appears to be nearly symmetrical, as is often the case with injury that occurred in the bud. Because the injury is so bizarre, many think that herbicides are involved. We cannot perform chemical residue tests at the clinic, but symptoms do not fit those typical of chemical injury. In all cases where other plant materials are growing nearby, only the oaks are affected, and sometimes one oak is affected, while nearby oaks do not show symptoms. Herbicides probably would not be so discerning. There is still much speculation that herbicides are part of the story. Anthracnose is not to blame for this condition, although anthracnose fungi might also be present.

One of our state foresters said that oaks on his property showed these symptoms last year. The leaf material continued to expand a bit, then new leaves emerged and more or less hid the affected leaves from view. In other words, the trees recovered. He is seeing symptoms again this year.

What do we suggest for action by the homeowner? Try to improve tree vitality so that the tree can con-tinue to produce new leaves. Usually this means watering the tree in periods of drought, removing dead wood, and fertilizing with a general tree fertilizer in the fall. If you have a healthy old oak tree with these symptoms, leave it alone. We will keep you posted as we learn more about this condition.

There is a picture of this condition on a University of Wisconsin horticulture publication, Deciduous Trees, Disorder: Springtime Weather Injury to Foliage, A2508. The picture can be viewed by going to the Web site http://www.uwex.edu/ces/wihort/ landscape/Landscaping_publications1.html and finding this publication under miscellaneous disorders.

Author: Nancy Pataky


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