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Oak Skeletonizer

June 3, 2003
We have seen this problem on white oaks for the past 5 or 6 years. In early spring, the foliage of white oaks appears “eaten,” with only the green veins remaining. The tissue that remains is the vein tissue and a bit of leaf blade around the veins. The edges of the leaf that remain are often brown or thickened like a callous tissue. Leaves look like what you might expect if a hoard of hungry locusts were to eat their way through the landscape. Insects, though, are not thought to be involved. We have seen this happen only on white oaks and occasionally on hackberry, leaving other nearby oak species unaffected. Often the problem appears in the middle of an oak grove where there are a few white oaks. Some names to refer to the condition include oak tatters, oak skeletonizing, and bare bones.

What is the cause of this condition? No one seems to know for certain. It has been suggested that this could 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 think that herbicides are involved. We cannot perform chemical-residue tests at the clinic, but symptoms do not fit those typical of plant-growth-regulator 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 might 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 in the necrotic tissue that is sometimes present.

There is some preliminary investigation into this problem being conducted at the University of Illinois. Funds are limiting for this sort of research, so work may not progress too rapidly. I will notify readers of any helpful information to which I am privy.

We hear most complaints of this condition from areas near farm fields as opposed to urban areas. The few people who have made follow-up comments have stated that leaves formed after this injury were normal. In other words, the trees appeared to recover. Although one year of such damage is not a threat to a mature oak, chronic injury may weaken the tree and predispose it to other problems, such as cankers, borers, oak wilt, to name a few.

What action do we suggest? Try to improve tree vitality so that the tree can continue to produce new leaves. For young trees, this usually means watering the tree in periods of drought, removing dead wood, and fertilizing with a general tree fertilizer in the early spring or late 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.

The USDA Forest Service has a pest alert called “Oak Tatters.” The publication number is NA-PR-02-00. This is easily found in an Internet search using “oak tatters” as the search word.

Author: Nancy Pataky


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