Oak disease discolors, drops leaves

Q. What is wrong with my oak trees? I have leaves that are dropping to the ground!

Patrick from Berlin Center

A. There are several possibilities based on the type of oak and a close examination of the falling leaves.

While there are concerns and reports of oak wilt in our area, we were able to rule this out because of the damage to the leaves. Oak wilt is going to show up within a few weeks of infection on red-black oaks. Usually in the heat of mid-summer, leaves will start to fall from the top of the tree first, looking dried up on the ends and having various changes in color towards fall brown. The tree can defoliate before Labor Day. While white oaks are susceptible to oak wilt, they can have symptoms and still survive for one or more growing seasons.

But Patrick’s leaves did not experience these symptoms. Several other callers had the same issues as Patrick, so something is happening to oaks.

By asking questions, we were able to determine the leaves were from white oaks – because of the rounded (not pointed) edges of the leaves.

There are two issues at hand. One is the browning of the leaves in spots, and some leaf browning that leads to falling leaves. This is typical damage caused by oak anthracnose. It is most likely due to the rainy spring we had here in the Valley. While the tree looks bad, this disease rarely causes any permanent damage. Raking the falling leaves can help reduce infections. White oaks are more susceptible to this disease than other oaks.

The other issue is bumps on the bottom side of the leaves. In most cases, there are spots on the top of the leaf that are mistaken for a fungal disease. But when turning the leaf over, the real culprit is observed. When these galls fall to the ground, they seem to jump because of the larva inside. This larva is a tiny gall wasp.

While these can be extreme in some cases, most cases are rather minor, with a few leaves falling in mid-summer. The extreme cases can cause many leaves to fall, but the tree will grow new leaves. Generally, these insects are harmless.

Keep watching out for your trees!

For more on oak anthracnose: http://go.osu.edu/oakanthracnose

To see pictures of the jumping oak galls: http://go.osu.edu/jumpgall

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office plant and pest clinic at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays.

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