Denise Ellsworth

Q: I have a smoketree that lost several major branches this year. The leaves just turned brown and wilted. I’d hate to lose this plant because it’s in a prominent place in my yard. I had a Japanese maple in the same location about 5 years ago, but it died too. Any advice?

A: Smoketree and maples are two of the many plants that are susceptible to a fungal disease known as verticillium wilt.

This soil-borne fungus infects through root tissue; the fungus then grows in the plant’s vascular system, plugging it up and causing wilting and dieback. Other symptoms of verticillium wilt include marginal browning of leaves, small leaves, stunting and sparse foliage.

Stress can also cause these symptoms, so if verticillium is suspected, I recommend sending a sample to Ohio State University’s Plant Pest Diagnostic Clinic for a lab diagnosis.

Because verticillium is soil-borne, proper diagnosis is important. If verticillium is confirmed, a replacement plant that is resistant to verticillium is recommended. On the other hand, it may be that a combination of stress factors caused both the maple and the smoketree to suffer in this location.

Q: My cranberry viburnum has lost nearly all of its leaves. They started to turn brown and blotchy, then they dropped. I am treating the shrubs for viburnum leaf beetle, and I don’t see any beetles or beetle damage. What could have caused this?

A: Cranberrybush viburnums commonly suffer from a leaf disease known as downy mildew. The pathogen is favored by cooler summers with ample periods of leaf wetness.

Damage from downy mildew starts off as light green spots that eventually grow together, forming angular lesions. These lesions turn brown, and when severe, the whole leaf will drop. On the undersides of the leaves, fungal growth can be seen.

Since the disease overwinters on diseased leaf tissue, cleaning up diseased leaves can be helpful in managing downy mildew. Also, avoid overhead watering, and enhance air movement by properly siting and pruning cranberrybush viburnums.

Incidentally, downy mildew is a completely different disease than powdery mildew, despite the similarity in names.

Q: I have seen many dead and dying trees as I drive through Ohio. Are we in the midst of a large disease outbreak?

A: It’s quite common to see trees in various stages of yellowing and browning in late summer, although this has nothing to do with “early fall color.” Depending on the type of tree you’re seeing, the problem could be caused by insect problems or by a disease. In general, there are no insects or diseases that can kill a large variety of tree species.

Black locust trees are commonly infested by a leaf miner that causes leaves to turn brown. By this time each summer, many trees look completely torched, but they come back with full vigor next year.

If you’re seeing elm trees dying, this is likely caused by Dutch elm disease. This fungal disease is spread from tree to tree by an insect vector. Young trees are not susceptible to the fungus, but elms become susceptible as they mature. For this reason, young saplings sprouting along roadsides may be healthy one year and dead the next.

We are now beginning to see major ash mortality in our area, so you may notice many dead ash trees of various ages along roadsides and fencerows. These trees were attacked and killed by the emerald ash borer. This pest has ravaged Ohio’s ash trees, and continues its march across the Midwest.

An assortment of different foliar diseases can also cause some leaf browning, such as various fungal diseases on horsechestnut, oak and ash trees. These diseases can sometimes cause a substantial number of leaves to brown and fall prematurely. In general, these diseases do not damage the long-term health of the tree.

Dead conifers along roadsides are most likely victims of stress, salt damage and fungal tip blight.

Q: Can you identify the insect problem on the enclosed maple leaves? Are they causing the leaves to turn yellow and red?

A: The only insects apparent in the bag you sent are two ladybird beetle larvae. These black insects are voracious predators of soft-bodied insects.

It is possible that aphids, spider mites, scale or some other soft-bodied insects had been living on the leaves before the ladybird larvae arrived. Since beneficial insects are present on the tree, it would be wise to avoid any kind of pesticide application. Such applications would kill the good bugs along with the bad.

Maple leaves, especially red maple leaves, commonly turn color earlier than other trees as summer wanes. This can be due to stress on the tree, and is not usually related to insect presence.

Denise Ellsworth directs the honeybee and native pollinator education program for the Ohio State University. If you have questions about caring for your garden, contact her at 330-263-3700 or click on the Ask Denise link on her blog at www.osugarden.com.