Hammerhead worm not yet found in Columbus. Expert answers questions about invasive species

Editors note: Throughout the growing season, Mike Hogan, OSU Extension Educator for Agriculture & Natural Resources in Franklin County, will answer gardening questions submitted by Dispatch readers. Send your questions to hogan.1@osu.edu.

Q: I recently read an online news story about a new invasive soil worm called the hammerhead found in northeast Ohio. Is this pest a concern here in Greater Columbus?

A: The hammerhead worm is a non-native species of terrestrial flatworm, and some of these strange-looking worms have been found in a couple of locations in northeastern and western Ohio this spring. 

These worms have not been found in central Ohio. The worms are native to countries in Asia, Africa, Australia and South America. Populations of these worms have become established in southern states in the United States. The worm is believed to have spread to Ohio in the movement of soil or potted plants and nursery stock from states in the southern part of the country.

This species of worm is thought to be invasive because it feeds on our beneficial earthworms as well as snails, slugs and insects. The long-term consequence of these worms in our Ohio ecosystem is not yet known, but they have not been found to be harmful or beneficial in other states that have had them for many years.

Flathead worms vary in size from an inch or less to 12 inches long. They can be brown or black and are slimy and shiny in appearance and can have a distinct crescent-shaped “hammer head”. These worms reproduce asexually, so gardeners who encounter them should not attempt to kill these worms by cutting them, as this act will just result in two worms! 

If you would encounter one of these worms, it's recommended that you wash your hands thoroughly, because the hammerhead does produce a toxin used in attacking prey.

These worms can be killed with salt, vinegar or rubbing alcohol.

Q: The azaleas  and rhododendrons  in our yard do not seem to be very healthy, and have few green leaves and very few flowers this spring. Is there a disease going around that is affecting these shrubs?

A: There are few diseases that affect both azaleas and rhododendrons, and we have not seen any widespread incidence of disease of these plants recently. What we do see pretty regularly in greater Columbus is a gradual decline of these acid-loving plants when they are not planted in areas with the correct cultural requirements. 

These plants do best in acidic soils with low pH, and the native soils in most areas of Franklin County are more alkaline with a high pH, due to the shallow limestone bedrock which serves as the parent material of these soils.

The best way to assess the pH of your soil is to have the soil tested for fertility and pH. For these plants to flourish in our soils, high levels of soil pH will need to be lowered by adding elemental sulphur to the soil where these plants are growing. Sulphur is available at any garden center.

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These plants also require well-drained, non-clay soils with ample moisture. When these plants are grown in clay-based soils with high pH levels, they tend to thin over time and flower production decreases over time. Many times, these shrubs are planted in foundation plantings close to the home, sometimes under the eaves, where soil moisture tends to be lower.

Additionally, planting these shrubs in open locations in the yard that receive full sun and are subject to windy conditions can also cause decline, as these plants grow naturally in woodland locations with shade and only dappled sunlight.

Whenever we see decline of azaleas and rhododendrons in the home landscape, it is typically due to cultural conditions and not insects or disease.

Q: Some small buckeye trees along a wooded ravine near our home have some leaves that have turned black and died this spring. We have a large buckeye tree in our front yard that does not seem to be affected. Is there a disease that  infects only wild buckeye trees?

A: This damage sounds like the work of the buckeye petiole borer. The caterpillar form of this moth seems to prefer small understory trees growing in wooded areas along streams. Rarely do we see damage from this pest on mature trees in woodlands or trees of any age in the home landscape. The pest infests both the Ohio buckeye (Aesculus glabra) and yellow buckeye (A. flava).

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This pest tunnels into the petiole, which is the small stem attaching the leaf to the tree branch, causing affected leaves to wilt, droop and turn dark green and black and eventually fall from the tree. Because this damage occurs in the spring, the symptoms are sometimes mistaken for frost or freeze damage.

Typically, only a few leaves are affected on a tree and the slight defoliation caused by the pest does not seem to affect the long-term health of the tree.