Exploring invasive plant species of Hancock County, Indiana


HANCOCK COUNTY — This time around we’re going to talk about the invasive plants found in our parks: what they are, what they do, where we can find them and we are doing about them.

We’ve got five that have been identified so far: Asian bush honeysuckle, autumn olive, Japanese honeysuckle, multiflora rose and garlic mustard. There may be more, but these are enough to keep us busy trying to eradicate them.

The main problem with all of these is that they damage forest communities by outcompeting native vegetation for light and below-ground resources and by changing forest structure. Some of them even put chemicals into the ground to discourage the growth of other plants.

Japanese honeysuckle: This is a native of Japan and Korea. It is a perennial woody vine that spreads by seed, rhizomes and runners. It was introduced into the United States in 1806 on Long Island in New York. It now occurs throughout 26 states and all 92 counties here in Indiana. We have found it in a couple of places: Beckenholdt Family Park and along the Pennsy Trail. Depending on how large the site is, we have found the best way is to cut and treat with an herbicide.

Asian bush honeysuckle: This is a native of Eurasia (Japan, China, Korea and Turkey). It is an upright shrub that can grow 6 to 15 feet tall. It is the first to leaf in the spring and the last to lose its leaves. It is found in a wide area of the United States. In Indiana, it tends to be in the upper two-thirds of the state. The problem is that the plants shade out everything on the forest floor. Again, the primary means of control is mechanical and chemical. We find this, again, along the Pennsy and in Beckenholdt.

Autumn Olive: This is considered a shrub and is easy to spot when the wind is blowing. The tops of the leaves are green, and the undersides of the leaves shine with a silvery color. It can tolerate poor soil, which is why we find it mostly along the Pennsy Trail. These bushes are native to China, Korea and Japan and came to the United States about 1830. It was used for the revegetation of disturbed habitats. This plant, like the others, suppresses plants that require direct sunlight. Cutting and herbicides are about the only way to get rid of this plant. Just cutting the plant causes vigorous resprouting.

Multiflora rose: This plant was introduced in 1886 as a root stock for rose growers. It also comes from Japan. In the 1930s the US Soil Conservation recommended its use for erosion control and as a living fence. However, it tends to grow into a dense thicket and smothers out other vegetation. This is the plant we are fighting at Thornwood. While it can be removed without the use of herbicides, it takes three to six mowings a year for two to four years to kill off the plant. We‘re using a combination of spraying then cutting as that has proved the most effective.

Garlic mustard: This is a biennial flowering plant brought from Europe by settlers. The plant was used for both food and medicine. The important point is, people eat it, and animals don’t. It will sprout one year, then during the second year it will shoot up in dense patches. A good stand of these in just one square yard can produce 62,000 seeds. Like most of the others, it also produces a chemical that inhibits the growth of other plants. There are a few plants at Thornwood, but with constant surveillance they can be removed before they cause much damage.

A good place to start checking for these would be inpaws.org; the site contains pictures and further information on these and other invasive plants. Some of these plants and others are illegal to buy or sell in the state of Indiana.

Joe Whitfield is the naturalist and gardener for the Greenfield Parks and Recreation Department. Send comments to [email protected]