“Pretty” Purple Plants Can be Pesky Plants

Many people will soon notice the pretty purple-flowered plants along roadsides, in ditches and fields, especially in wet areas. But, that pretty plant can be very invasive and damaging to other wetland plants, which can reduce the effectiveness, diversity and ecological balance of the wetland area. The plant is purple loosestrife. The pretty flowers eventually turn into enormous quantities of tiny seeds that get spread throughout the wetland and create a seed bank that will last for years to compete against desirable plants.

Purple loosestrife was introduced into North America in the 1800's and into Illinois in the mid-1900's. It has only become a real problem in the last 20 to 30 years. The plants can become 4 to 6 feet tall and have massive root and stem systems. High densities of purple loosestrife can create heavy mats that native wetland plants cannot compete with effectively. The loss of native plants can eventually mean the loss of native wildlife in the area and possibly even a reduction in the natural ecological effectiveness of the wetland.

Many types of controls have been used, but mowing, weeding, burning or using herbicides have not been effective on large scale areas and may be too labor intensive or costly. The problem is that the millions of seeds left in the soil when plants are allowed to reproduce can send up new and more plants year after year.

Researchers at the Illinois Natural History Survey in Champaign are currently evaluating biological control of the weed through the use of beetles that are natural enemies to the plant. The method has shown to be effective in many parts of the state, at least in small infestations.

For individual landowners, the main consideration is to not encourage and enable the spread of the plants. Do not move plants from one location to another. Control small patches early by cutting off flowers to eliminate seed heads or other control methods. Monitor the spread of the plant in the area and report significant increases to the survey researchers. Do not purchase plants that may be suspected to be purple loosestrife. The Illinois Natural History Survey loosestrife website is www.inhs.uiuc.edu /cbd/loosestrife /bcpl.html.

June-July 2003: Herbs | "Pretty" Purple Plants Can be Pesky Plants | Long Term Planning Leads to Successful Gardening | Honey Bees, Wasps and More | Rust Diseases on Home Lawns