Using a Plant’s Lifecycle Against Itself: A Timeline for Controlling Reed Canary Grass and Common Reed
One of the key elements in any restoration project is to eliminate or suppress aggressive native and non-native species. Herbicides are often the best option to kill these plants, but the damage caused to non-target species from improper timing or misapplication can be irreversible. We have found it is best to study the trends, habits, and life cycles of invasive plants before making a decision to use herbicides. In this way, we gain insight into the best time and easiest way to control these plants. In this article, we discuss how we have put this technique into practice to control Reed Canary Grass (Phalaris arundinaceae) and Common Reed (Phragmites australis).
Reed Canary Grass and Common Reed are cool-season grasses that grow primarily during the spring and fall in moist soils. Individual plants can reach a considerable size before the warm season grasses and forbs begin to break the soil surface. Growth usually radiates outward from the initial point of infestation by a lengthening root system. The roots will continue to spread unless interrupted by changes in soil moisture or manmade obstructions. The seeds of Common Reed seem to have limited viability and we find this to be true for Reed Canary Grass as well (Runkel and Roosa, 1989 and Swink and Wilhelm, 1994). This indicates that the strength is in the roots. The spreading root system of both plants make them extremely resistant to controlled burns and makes removal by hand virtually impossible. Therefore, herbicide is the only option left.
We have found that using a timed application of Glyphosate-based herbicide such as RoundUp™ at a low concentration of about 1 to 2 percent (1 to 2 gallons of concentrate in 100 gallons of water) will kill Reed Canary Grass and Common Reed while still maintaining a viable native population. For example, we are successfully using a 2 percent solution of Glyphosate to control Reed Canary Grass in the fall on our own property in Leland, Illinois, without killing Wild Iris (Iris virginica) growing in the same area. When treating small stands, we use a backpack sprayer to apply the herbicide. When treating infestations that cover an acre or more, we use a tree gun attached to a 200-gallon Hypro™ pump with a 400-foot long hose. This device allows us to spray close up and at long distances. For even larger areas of solid stands, we have used a Polaris 6 X 6 ATV with a 12-foot boom sprayer. All three methods depend on the area being sprayed and enable precision spraying, limiting disturbance and damage to the native population. Proper conditions must be taken into account such as wind speed and precipitation. In fact, it is better not to spray in areas with remnant quality if the wind speed is over ten miles an hour.
Using information about the life cycle and growth of Reed Canary Grass and Common Reed, we have developed the following management timeline. This timeline is specific for Northern Illinois where we have done our work. Your site will be different and conditions need to be taken into account before applying this technique. It is best to start in spring, but you can pick any point to begin as long as the schedule is kept.
· April. Identify the areas to be treated. Reed Canary Grass and Common Reed will retain much of their upright structure from the previous year. When you begin to see the present year’s growth, mark the area of interface between the native population and the undesirable grasses. We stake this area with steel rebar because it is long lasting and will not burn (Figure 1).
· May-September. In large infestations of continuous weed foliage, herbicide anytime during this time frame from the center of the infestation to the internal edge of the interface. For smaller patches of weed species mixed with natives, spray in early May to reduce damage to the newly emerging natives. In both scenarios, many of the native species will still be underground early in the season, and protected from pesticide drifts.
· October and November. Spray herbicide on the interface when the native warm-season species have gone dormant and the cool-season grasses are still active. Pay attention to what is being sprayed. If a plant is green, it is still active and will take up this herbicide, regardless of species.
· November-March. Conduct a thorough controlled burn. This will remove the dead leaf matter and help bring light to the surface for the native plants. A controlled burn can be conducted anytime during these months as long as the temperature is above freezing. We have conducted a successful controlled burn at the Leland property in February when there was no snow on the ground, but the wetland and ground were still frozen. Burn season is whenever the conditions are right, not when the calendar month has changed.
· April and May. Spot-treat remaining infestations marked by the rebar before native plants become active. Use the same Glyphosate based herbicide and the same 2% concentration as earlier in the year.
· May-July. Once we have cleared the invasive grasses from the area, we reduce the risk of further invasion by immediately replanting the site with native species. Areas with remnant quality may have a substantial seed bank in the soil and will not require immediate plantings.
Retreat and burn as necessary.
Our results have been variable at different locations, but one thing is constant. There is a reduction every year from the previous year of these problem species. In two separate plots, 20’ X 20’, on our property in Leland, we had 95% to 100% coverage of Reed Canary Grass on 3/1/00. After the first treatment, it was reduced to between 5% and 10% coverage in April 2000. There were resprouts in the fall of 2000, but less than 5% coverage. A fall spot treatment showed a 100% kill as expected, and resprouts were not unexpected. This year there were spring resprouts up to 40% coverage in the first plot and only 10% coverage in the second. There will be more resprouts in the spring compared to the fall because spring is the primary growing season. The key thing to remember is that every site is different and environmental conditions will make the plants respond differently every time. For an in depth look at diversity issues related to Common Reed, please refer to Ailstock, Norman, and Bushmann in Restoration Ecology, March 2001.
Ailstock, M.S., Norman, C.M. and Bushmann, P.J., 2001. Common Reed Phragmites australis: Control and Effects Upon Biodiversity in Freshwater Nontidal Wetlands. Restoration Ecology, pg. 49-59, vol.9, no.1, March 2001.
Roosa, Dean M., and Runkel, Sylvan T. 1989. Wildflowers of the Tallgrass Prairie. Ames, Iowa: Iowa State University Press.
Swink, Floyd and Wilhelm, Gerould, 1994. Plants of the Chicago Region. 4th ed. Indianapolis: Indiana Academy of Science.