Maryland Efforts to Control Purple Loosestrife

Maryland's 30 day successful pursuit of purple loosestrife on MD 176.

Before

After

For years the traveling public has admired the magenta colored flowering spikes of Purple Loosestrife blooming in New England and the Midwest. When the Maryland State Highway Administration first started planting wildflowers in 1986, we received a number of requests to add Purple Loosestrife (Lythrum salicaria) to, our wildflower seed mix, We knew from our association with other DOTs across the nation and the FHWA just how invasive Purple Loosestrife had become so resisted any temptation to intentionally spread the invasive weed further.

At least so far, Purple Loosestrife has not become the invasive weed that it is other states. Until recently, it wasn't even considered an invasive weed in Maryland. The Maryland Invasive Species Council now lists the plant as an invasive species. Along Maryland highways, Purple Loosestrife can be found on less than 2 acres, mostly in ditches It can be found off of the highway right-of-way but not to the extent that it can be found in states further north and west of us.

Until recently, controlling invasive vegetation along Maryland's highways has pretty much been limited to Johnsongrass, Phragmites and thistle with Canada Thistle being our number one priority. In recent years we have adopted a more integrated approach to controlling invasive species. We now promote multiple tools to control invasive vegetation such as planting competition, mowing, herbicide application, and biological controls. In addition, we have expanded our target species to include some of the other bad guys such as Ailanthus (Tree of Heaven) and now Purple Loosestrife.

This summer I received a request from our Environmental Programs Division to control Purple Loosestrife in a ditch near the parking lot for State Highway's Office of Maintenance (see photo). Their concern was that the ditch leads into a storm water management pond which could spread the loosestrife into nearby wetland mitigation sites. At first, I had planned an using the non selective aquatic herbicide, Rodeo, but I didn't want to kill all the grasses in the ditch. Because of the drought last year, I decided to use the selective herbicide, Escort, which is labeled for low lying areas where water has drained. In early September 2002, our contractor applied one ounce of the Escort in five gallons of Thinvert per acre. Two weeks later 90% of the Purple Loosestrife had been controlled. Next year we plan to expand our efforts to control Purple Loosestrife along Maryland's highways.