Extension News

Recognize and Control Invasive Woody Plants


By Robert Hartzler
Weed Specialist
Iowa State University Extension

Iowa’s natural areas are under attack by exotic plants that degrade these valuable spaces. Invasive plants displace native species, disrupt ecosystems and interfere with recreational uses of prairies, woodlands and other areas.

A number of factors contribute to the growing problem with invasive woody plants; however, disturbance is the universal factor that plays a key role in the success of these weedy plants. Since Iowa’s few remaining natural habitats are highly fractured and often exposed to disturbances (grazing, logging, nutrient runoff, etc.), the threat of invasive plants is constant.

While a wealth of information is available to aid in identification and management of invasive woody plants, much of the information about control tactics is directed toward people experienced in weed management. This article and a future one will provide information appropriate for people who have little experience in controlling invasive woody plants.

Woody invasive plants of Iowa

Buckthorn - Several species of buckthorn are considered invasive in Iowa, but common buckthorn (Rhamnus cathartica) is most prevalent. Buckthorn plants are commonly found on the edges of wooded areas and are easily spotted in the spring or fall since they leaf out earlier and retain their leaves later than native trees. Buckthorn is a shrub or small tree that can reach heights of 25 feet. Leaves are oval and dark green with three to four pairs of curving veins. Twigs are usually tipped with a sharp spine, the source of the plant’s name. A useful identification trait is the yellow/orange tissue found immediately under the bark.

Honeysuckle - There are several invasive honeysuckle species in Iowa. Honeysuckle plants form a clump of arching stems that can reach heights of 10 to 15 feet. Like buckthorn, they leaf out early and retain their leaves late into the fall. Leaves are arranged opposite on the stems and in the spring are light green. The bark is grey to tan in color with distinct stripes.

Multiflora rose - This plant was introduced as rootstock for cultivated varieties and planted for numerous purposes for many of which it was poorly suited. It grows best in open areas such as pastures and prairies, but can survive in wooded areas. Individual plants can reach heights greater than 10 feet. Multiflora rose can be differentiated from native roses by the fringed stipules present at the base of leaf petioles (small, leaflike appendages at the point where the leaf stem attaches to the supporting branch). Native roses have stipules, but they have smooth margins.

Control strategies
Several control tactics are effective against woody plants. The most appropriate method varies depending on plant size, density, type of habitat and time of year. Smaller plants often can be pulled from the soil by hand or with specially designed tools. Mechanical removal of the brush or tree is an effective tactic, although many weedy species will re-sprout following removal of the stem. Repeated mowing can be effective against brushy species such as multiflora rose. Herbicides can be used to control re-sprouting.

Three distinct types of herbicide treatments are commonly used to control woody plants: cut surface application, basal bark application and foliar application. Herbicide treatment will be covered in a future article.

Acknowledgement: Loren Lown, Polk County Conservation Board, provided valuable assistance in developing this article.

Additional information about invasive plants of Iowa and surrounding states
Midwest Invasive Plant Network: http://mipn.org/index.html
Common Roadside Invasive Plants in Iowa: http://www.iowalivingroadway.com/invasiveplants.asp

This article is from the May 2009 issue of Acreage Living. Other articles in this month’s issue—
Citizens can be Key Partners in Iowa NatureMapping
Spring is a Good Time to Test Well Water


Contacts :
Robert Hartzler, Agronomy, (515) 294-1923, hartzler@iastate.edu

Lynette Spicer, Extension Communications and External Relations, (515) 294-1327, lspicer@iastate.edu