The Plant Clinic has seen many cases of oak tatters or “bare bones” on oaks in the last few weeks. It may not be a problem, but it looks quite bizarre. The disease affects the oak leaves, and much of the leaf is just “gone.” Only the vein tissue and a bit of leaf blade around the veins remain. They appear to have been eaten by a voracious insect that prefers non-vein tissues. The edges of the leaf that remain are often brown or thickened like a callous tissue. While some people refer to this as oak tatters, our own Bruce Paulsrud calls it the bare bones disease.
What causes this condition? We don’t 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 occurs in the bud. Because the injury is so bizarre, many people think that herbicides are involved. We cannot perform chemical residue tests at the Plant Clinic, but the symptoms are not typical of chemical injury. In all cases where other plant materials are growing nearby, only oaks are affected. Herbicides would not be so discerning. Anthracnose is not to blame for this condition, although anthracnose fungi might also be present. I have seen many cases of this condition, and I strongly believe that oak tatters is a reaction to weather stress and nothing more.
What should the homeowner do? Try to improve tree vitality so the tree can continue 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.
University of Wisconsin Extension has a picture of this condition on their Web site. Go to http://www. uwex.edu/ces/pubs/hortcat.html; then click on “Trees and Shrubs.” This picture was taken from Deciduous Trees Disorder: Springtime Weather Injury to Foliage, University of Wisconsin publication A2508.