by Brenda Zollitsch
Over the last year, ASWM has received numerous questions about what leads to non-native plant invasions, how to prevent them, the effect of invasive plants on wetland mitigation sites and more. This past week we received a request for information after a landowner noticed non-native Phragmites plants in an area that had been previously invasive-free. The impacts of invasive Phragmites on wetlands can be significant. This blog will outline some of the basic information you need to know about Phragmites and identify follow-up resources for more information.
What is Phragmites australis?
According to the U.S. Department of Agriculture’s Phragmites Field Guide, Phragmites australis is considered to be one of the most widespread plants on earth and is found in marsh systems world-wide. There are three kinds of Phragmites in North America: 1) Native Phragmites (also known as common reed) which has been in the US for thousands of years, 2) invasive (introduced) Phragmites from Europe which has only been present in the US for less than 200 years, and 3) a “Gulf Coast type” that has an uncertain origin and introduction history. The plant was grown commercially in Europe throughout the 20th Century, primarily used as thatch for roofs. The introduction of invasive Phragmites in the United States is thought to have occurred through the emptying of ballast material from European ships.
Why is Phragmites australis a problem?
Phragmites of European origin has a robust ability to reproduce in a wide range of conditions and through a number of means, including both through wind and water dispersion of seeds and through rhizomes and rhizome fragments). This highly adaptable and resilient plant can live and reproduce in freshwater, brackish or even salt water. Recent studies have shown that the invasive form of the plant is now present in all 50 states. Michigan Coastal Program also points out that physical and chemical disturbances provide Phragmites with a “competitive edge.”
Not only is the plant good at replicating itself, it is difficult to remove. Phragmites has deep and complex root systems which extend out both vertically and horizontally. It is important to note that it can reproduce from simple fragments of rhizomes. For this reason, the invasive version of the plant is often found on disturbed sites. USDA indicated that the plant is often attracted to areas where nutrient inputs are high, i.e. where there has been development. Most common areas for invasion are saturated roadsides, construction sites, adjacent to agricultural fields, or near developed shorelines.
Its effects are somewhat insidious. First, with its reproductive strength and robustness, Phragmites often overtakes native species that are critical to local ecosystem health. According to the Great Lakes Phragmites Collaborative, biodiversity is often lost on sites where non-native Phragmites is present, as the site hydrology is altered by the presence of the plant (greater sedimentation, plant litter build-up). This, in turn, reduces the regular flooding of the wetland and reduces the ability of wildlife to feed on the wetland surface.
What can be done to reduce the spread of Phragmites australis?
Michigan’s A Guide to the Control and Management of Invasive Phragmites (2014) outlines the four primary control methods for Phragmites. Their recommendations are summarized here:
1) Herbicides: Glyphosate and imazpyr
Herbicides, such as glyphosate and imazpyr can be used individually or as part of a combined control strategy and usually require multiple-year treatments. Spot treatment is possible and recommended. However, these herbicides are nonselective and will enter any plant species (native or non-native) that comes into contact with the chemicals.
There are many different methods for applying these herbicides, including injecting stems, hand swiping, backpack sprayers, wick or dauber, boom sprayers or aerial application). Largescale or non-targeted applications of these herbicides are likely to negatively affect adjacent plant communities. Perhaps most compelling, a wide range of research studies have shown negative health effects to humans and ecosystem health from contact with these chemicals. It should be noted that well-established stands of Phragmites are difficult to control with only one herbicide treatment. Anyone who plans to spray plants which are in the water or growing from ground which is below the “ordinary high water mark” (OHWM), should contact their state environmental agency for more information about compliance with water quality regulations. For general information about herbicide treatment of Phragmites, go here. For specific treatment details, refer to specific product information.
2) Prescribed Fire
After an initial treatment, prescribed fire can be used. Fire can be used in conjunction with herbicide treatment in the year following herbicide treatment to removes plant biomass. Fire destroys seed heads, removes dead stems, and kills plants that survived herbicide treatment. Additionally, prescribed burning promotes native plant growth. However, beware — the use of fire without herbicides may actually promote invasive growth rather than discourage it.
3) Physical Removal
When burning is not feasible, physical removal is an option. However this must be done carefully, as the roots can break into many pieces, each of which will grow into more Phragmites. Mechanical removal can be done using weed whips, small mowers, brush hogs, flail mowers, or hand-cutting stems. Physical removal efforts should wait for an adequate period of time after any herbicide application to allow absorption of the chemical. Results are improved when cutting occurs once the ground is frozen. Some research indicates that this method can be used independently from herbicide treatment, but is more effective when used in conjunction with it.
4) Flooding/Water Management
Flooding after herbicide treatment has been effective under certain conditions. Increasing water level alone is not effective in controlling Phragmites and drawdowns can make Phragmites growth increase. It should be noted that a state may require one or more permits to release water for this (or any other) purpose.
What are the Impacts of Glyphosate Use?
With the recommendations from almost all sources focusing on the use of herbicides (and particularly application of glyphosate), information about the impacts of glyphosate use is warranted. While the EPA formally considers glyphosate to be non-carcinogenic, the federal agency has not reviewed this status since 1993. More recent studies have found significant associations between glyphosate exposure and, as well as both liver and kidney damage and provide some evidence that glyphosate formulations are much more toxic than glyphosate alone. A recent report by the World Health Organization declared glyphosate “probably causes cancer”.
As a result, state and federal agencies are being asked to review this and other evidence to decide how to label it. All of this points to a need to more carefully study and monitor these effects. However, according to the National Pesticide Information Center, glyphosate is not included in compounds tested for by the Food and Drug Administration’s Pesticide Residue Monitoring Program nor in the United States Department of Agriculture’s Pesticide Data Program.
If not Herbicides, What are the Alternatives?
The bottom line is that there is little else that has been shown as cost-effective on a broad scale. While some efforts have been made to explore alternatives like the effectiveness of covering plants and grazing as tools to control Phragmites, these are not viable large-scale solutions at this time.
Some Parting Thoughts
Studies identifying unintended impacts on humans and wildlife from the use of pesticides are cause for concern. So is the lack of effective alternatives. Phragmites is just one of many plant and animal species replacing native plants and animals in the U.S. and other countries. For plants at least, they are often opportunistic, early successional species that thrive in compacted disturbed soils where nutrients are provided in large concentrated pulses. In fact, many of these plants have followed humans around the world for centuries because human land use practices create ideal habitat.
It is becoming increasingly apparent that pesticides are a short term solution at best. There is mounting evidence that over time the use of pesticides yields pesticide resistant strains of nuisance species. Scientists, land managers and others need to pursue a deeper understanding of the issues and drivers that allow nuisance species to replace native species and persist on the land. For example, can we change land management practices such as compaction of soil and applications of fertilizers to discourage invasive species? Alternatively, are there ways to accelerate plant succession to replace invasives such as Phragmites with desirable plant species? With recent studies and legal cases linking glyphosate with various forms of cancer and other adverse health effects, the availability of herbicides as a tool to control invasive species may be limited in the not too distant future. Alternative approaches are needed.