More info for the terms: cover
, invasive species
, long-term effects
, prescribed fire
, root crown
, species richness
Reed canarygrass is generally considered highly invasive within most of its North American range [37,133,148,168,197,251,303]. Several attributes may contribute to reed canarygrass' invasiveness in North America. Under cultivation, different strains of reed canarygrass vary greatly in vigor of growth, leafiness, seed retentioin, seed production, and resistance to drought  which may influence its invasiness. A review by Maurer and others  suggested that reed canarygrass is invasive because of high energy allocation to reproduction, clonal growth, long growing period, rapid growth, high productivity, and a broad tolerance to environmental variability. Under experimental conditions, reed canrygrass' rapid growth rate, tall leafy shoots, and extensive lateral spread of the canopy and rhizomes allowed it to effectively capture light and nutrients even under low nutrient and soil moisture conditions . Disturbance may enhance reed canarygrass' invasiveness. In a controlled environment, reed canarygrass was more invasive where disturbance was common versus sites where little disturbance occurred .
Impacts: Hutchison  considered the nonnative type of reed canarygrass to be a "major threat" to North American wetlands, and NatureServe  gave reed canarygrass an impact-ranking of "high" based on its negative impacts to wetlands and riparian areas. Some of reed canarygrass' ecological impacts have been well documented, particularly in the Northwest and Great Lakes areas [15,31,35,66,145,188,234,240,248]. Reed canarygrass impacts ecosystems by reducing plant diversity [15,16,66,145,176,234], and may degrade wildlife habitat [35,110,210,248,270], interfere with wetland restoration [5,155,240,279], impede water flow [46,110], and/or influence succession.
Reed canarygrass is widely considered a threat to native wetland plant communities [5,23,58,122,144,188,195,256], and several studies document a loss of diversity in invaded communities [15,16,66,145,176,234]. In an Oregon riparian forest, increasing reed canarygrass abundance was correlated with decreasing species richness (R²=0.2455) and understory species diversity (R² =0.327) in stands older than 7 years . In coastal wetlands in Oregon, high reed canarygrass cover near beaver impoundments was associated with a significant (P=0.01) reduction in species richness when compared to sites with low reed canarygrass cover . In Wisconsin, Kercher and others  noted 21% fewer species in wetland plots containing reed canarygrass compared to reference plots, and 52% fewer species on sites where natural hydrological regimes had been altered. On a river island in Wisconsin, increases in frequency of nonnative grasses, including reed canarygrass, corresponded to decreases in frequency of numerous herbaceous species common to the island. The researcher concluded that reed canarygrass had a "major impact on plant species composition and diversity on the river island" .
Frequency (%) of common herbaceous species on a river island in Wisconsin over a 15-year period [15
] Plant species Native status Growth habit 1981 1996 switchgrass
(Panicum virgatum) Native perennial 54 24 Canada wildrye
(Elymus canadensis) Native perennial 22 25 marshpepper knotweed
(Polygonum hydropiper) Nonnative annual 14 2 prairie cordgrass Native perennial 12 20 prairie ironweed
(Vernonia fasciculata) Native perennial 9 3 tufted lovegrass
(Eragrostis pectinacea) Native annual 7 2 Kentucky bluegrass Nonnative perennial 7 14 reed canarygrass Unclear perennial 2 17
Reed canarygrass may displace rare plants like Nelson's checkerbloom (Sidalcea nelsoniana) in Oregon  and water howellia (Howellia aquatilis) in the inland Northwest .
Although there is concern for reed canarygrass' impacts to wildlife habitat (reviews by [5,110,210]), as of this writing (2010) there has been little documentation of these effects. In southwestern Minnesota and Wisconsin, Kirsh and others  studied riparian wet meadows dominated by reed canarygrass and their use by 4 common species of breeding birds. They determined that reed canarygrass had a negative effect on 1 species and a slight positive effect on 2 species . Columbian white-tailed deer graze on reed canarygrass but prefer native wetland plant communities over monotypic stands of reed canarygrass . In a survey of 12 western states, biotic integrity—based on vertebrate and macroinvertebrate occurrence— was significantly (P<0.001) lower on sites in mountainous regions where reed canarygrass occurred than where it was absent . In western Washington, 158 coho salmon (an endangered species) migrating upstream during a high flood event became stranded and died in a field of reed canarygrass and pale-yellow iris (Iris pseudacorus) when flood waters receded quickly. Carrasco  speculated that dense stands of reed canarygrass and pale-yellow iris made escape from the field more difficult for the coho salmon, especially where the canal was ill-defined. The displacement of woody vegetation by reed canarygrass may reduce the number of arthropods foraging in riparian areas, which may in turn deprive juvenile salmon of an important food source (review by ).
Because reed canarygrass establishes in constructed or restored wetlands, it may interfere with the long-term success of wetland restoration projects [5,31,155,240,279]. On an experimental site in Minnesota, researchers evaluated the potential for native lakebank sedge (Carex lacustris) to establish in a former wetland dominated by reed canarygrass. After 3 years, mean biomass of sedge planted in plots with reed canarygrass was either unchanged or decreased . Researchers in Minnesota speculate that reed canarygrass' large seed bank hinders wetland restoration .
Reed canarygrass may influence hydraulic flow of a streams [5,46,110]; however, empirical evidence is lacking. One review suggested that reed canarygrass impacts hydraulic characteristics of surface waters by clogging ditches and streams with thick thatch . Comes and others  speculated that roots and rhizomes of reed canarygrass come in contact with water and moist soil, collecting silt and rapidly forming berms at the water's edge. Silt deposits and the emergent stems and leaves of reed canarygrass reduce the volume of water that a channel can carry and thus impede water flow . An invasive plant guide from Alaska claims that reed canarygrass may slow stream flow and eliminate the scouring action needed to maintain salmon habitat .
Control: Reed canarygrass is difficult to control because it has vigorous, rapidly spreading rhizomes and forms a large seed bank [69,105,232,240]. Because reed canarygrass is typically found in wetlands, implementation of herbicide applications , mowing , or prescribed fire (, review by ) may be hindered or impractical on many sites. Additionally, past and present use of reed canarygrass for forage and erosion control may frustrate attempts to control it in wildlands .
Management strategies used for reed canarygrass control include mowing, herbicide, grazing, cultivation techniques, fire, shading, and flooding (review by ). Like control of most biotic invasions, control of reed canarygrass is most effective when it employs a long-term, ecosystem-wide strategy rather than a tactical approach focused on battling individual invaders . Various types of publications including original research [1,18,148,161,260,305], reviews [184,251,277], and regional invasive plant management guidelines  generally agree that control of reed canarygrass is most effective when it includes an integrated approach implemented in a sequential and timely order. Implementing treatments based on reed canarygrass' growth characteristics and phenological stages (see Seasonal development and Seedling establishment and plant growth) may make it more vulnerable to treatment [1,251]. Regardless of which treatment options are used, the potential for post-treatment reinvasion by reed canarygrass [69,232] or other invasive species  should be considered. Ongoing maintenance to control sprouting and seedling establishment may be necessary to maintain long-term reed canarygrass control [1,161,305].
Prevention: It has been argued that the most cost-efficient and effective method of managing invasive species is to prevent their establishment and spread by maintaining "healthy" natural communities [186,258] (e.g., avoid road building in wildlands ) and by monitoring several times each year . Managing to maintain the integrity of the native plant community and mitigate the factors enhancing ecosystem invasibility is likely to be more effective than managing solely to control the invader .
An invasive plant management guide suggested that reed canarygrass might be prevented from invading wetlands by constructing erosion screens and catch-basins around wetlands adjacent to eroding slopes . Mauer and others  speculated that disturbance that creates canopy gaps may make a community more vulnerable to invasion by reed canarygrass and recommended maintaining a dense canopy to discourage reed canarygrass invasion. They also recommended the quick removal of new populations of reed canarygrass to prevent its spread .
Cultural control: Shading has been suggested as a control for reed canarygrass [5,119,149,236]; however, reed canarygrass' response to shade is not well understood . Results from field and laboratory studies indicate that shade may reduce reed canarygrass' aboveground biomass but not its tiller production (see Shade tolerance).
Seeding and planting of native species have been used in conjunction with other treatments to control reed canarygrass (see Integrated Management and Use of prescribed fire), although reed canarygrass may quickly displace planted or seeded species if its rhizomes are not removed . In reed canarygrass infestations, planted woody species may survive better than seeded species . In Washington, within 2 years after planting willows in a monotypic stand of reed canarygrass, its biomass was reduced by 56.1% (where plantings were 0.91 m apart) and 68.0% (where plantings were 0.60 m apart) relative to controls. The decrease in reed canarygrass was attributed to increased shade from willows . To control reed canarygrass, Iannone and others [134,135] encourage the use of long-lived native perennial species rather than native annuals or short lived-perennials [134,236], because the latter may prevent desired native species from establishing and result in a reed canarygrass-dominated community .
Hydrological manipulation: Reed canarygrass may establish by seed and/or rhizomes following drawdown, even on sites treated with herbicide . Some have speculated that the draining of wetlands for agriculture may help to spread reed canarygrass  and that restoring water levels may help control reed canarygrass .
Flooding has been suggested as a control for reed canarygrass [133,137,153,167,251], and several studies have evaluated its potential. In Oregon, within 1 year of restoring historical flooding regimes to a slough, reed canarygrass cover was reduced by as much as 10.7% . A Wisconsin marsh had been dominated by reed canarygrass, but it was nearly eliminated following 3 years of flooding and a subsequent drawdown . In the greenhouse flooding to a depth of 2.6 inches (6.5 cm) above the soil surface for 1 month decreased rhizome survival and aboveground biomass by as much as 20% compared to plants grown in saturated or moist soils . A study from the Czech Republic indicated that reed canarygrass' rhizome growth and tillering may be reduced by flooding, particularly flooding in the summer .
Occasionally reed canarygrass responds favorably to flooding. Reed canarygrass established in wetlands that were reflooded following a 5-year-drawdown . In a controlled environment, reed canarygrass biomass was greater for plants exposed to prolonged flooding compared to nonflooded plants .
Flooding may be most effective at controlling reed canarygrass when timed to coincide with maximum rhizome growth and tillering [137,153] (see Seasonal Development). Lavergne and Molofsky  concluded that more empirical data are needed to assess whether hydrological manipulation, especially water levels and inundation periods, could limit reed canarygrass' vegetative spread. Gillespie  cautioned that using flooding for reed canarygrass control may be costly and water levels difficult to manipulate.
Physical or mechanical control: Hand-pulling reed canarygrass is too labor intensive and time-consuming for large stands (review by ), although it may be effective for controlling small stands (reviews by [8,119,133]). In an oak savanna in Wisconsin, hand-pulling controlled reed canarygrass when treatments were carried out 2 to 3 times a year over a 5-year period . Covering reed canarygrass with black plastic or fabric may kill small stands of reed canarygrass [5,105,119,177,279], but rhizomes may survive (review by ). Covering may be more effective at controlling reed canarygrass if done in conjunction with other treatments such as mowing and native plant seeding [105,177].
Mowing, plowing, cutting, raking, and disking have all been evaluated for reed canarygrass control. If used independently, mechanical control typically produces short-term reed canarygrass control at best ([95,148,240,301], review by ). Often there is no long-term effect ([95,148], review by ), because reed canarygrass grows back from the seed bank [148,240] or may sprout from rhizomes or produce tillers from the root crown (see Vegetative regeneration). In some instances, cutting may increase reed canarygrass growth (review by ) and mowing may increase tiller production . Mechanical treatments may be more effective at controlling reed canarygrass when included as part of a well coordinated integrated management plan.
Biological control: As of this writing (2010), no biological control agents have been developed for reed canarygrass. Reed canarygrass may not survive sustained grazing [97,283], but grazing may be impractical for reed canarygrass control in wetlands (review by ).
Chemical control: Some herbicides control reed canarygrass (review by ), especially when used in conjunction with other treatments such as fire, mechanical control, and/or native seed dispersal (see Integrated management). Studies documenting the long-term effects of herbicide treatments have found that when used independently, herbicides may provide short-term reed canarygrass control at best [1,69,105,177]. Even when used in conjunction with other treatments, several herbicide applications may be necessary to prevent its reestablishment from the seed bank or rhizomes [1,69,105,119,240,279,305]. In Tennessee, 1 application of herbicide failed to prevent reed canarygrass seedlings from establishing in a monotypic stand and may have facilitated germination by creating canopy gaps . In Minnesota, 2 herbicide treatments (1 in late August and 1 in late September) did not reduce reed canarygrass seed bank densities compared to control plots (280 seeds/m²), but 2 years of herbicide treatments did (60-120 seeds/m²). Repeated late-season herbicide treatments, however, did not prevent remaining seed from germinating [1,305].
Herbicide treatments, whether used independently or in conjunction with other controls, may be more effective when timed to take advantage of reed canarygrass' vulnerable phenological stages (, review by ). Rosburg  suggested that early spring or late fall herbicide applications, coinciding with reed canarygrass' photosynthetically active periods, may improve herbicide selectivity and avoid stressing native species. In Minnesota, 2 years of fall herbicide applications, timed to coincide with optimal carbohydrate accumulation in reed canarygrass rhizomes, were twice as effective at controlling reed canarygrass as 2 years of spring applications . In the eastern Great Plains area, reed canarygrass rhizomes survived spring herbicide applications; however, late October and early November application killed reed canarygrass rhizomes completely .
Glyphosate products, approved for use in aquatic environments, have been used to kill reed canarygrass [1,69,148,161,177,240,260,305] and are commonly recommended ([46,105,263], reviews by [5,133]) for its control. One study from Illinois  and another from Wisconsin  evaluated using sethoxydim to control reed canarygrass. Both studies indicate that, when used in conjunction with fire and glyphosate, sethoxydim may improve opportunities for native plants to establish [260,305] (see Use of prescribed fire); however, its use is limited to sites without standing water . Occasionally, amitrol and dalapon have been recommended for reed canarygrass control, but they may not be appropriate for use in wildlands and aquatic environments ([46,116,263], review by ).
Herbicides are effective in gaining initial control of a new invasion or a severe infestation, but they are rarely a complete or long-term solution to weed management . Additionally, most herbicides are not selective enough to treat reed canarygrass on wildlands ([177,263], review by ). See the Weed control methods handbook  for considerations on the use of herbicides in natural areas, particularly wetlands and riparian areas, and detailed information on specific chemicals.
Integrated management: Numerous studies [1,69,148,149,161,177,260,305] have evaluated various integrated management approaches to control reed canarygrass, and several offer potential control treatments [1,148,149,161,260,305]. Researchers have used combinations of mowing, herbicide, and fire to control reed canarygrass, and to a lesser extent disking, shading, black plastic, and flooding [1,5,69,148,149,161,177,200,260,305]. Treatments often include or are followed-up with a seeding or planting of native species [69,105,149,161,260,305]. Successful strategies require a multiple-year commitment including long-term maintenance. To obtain optimal results, treatments are typically carried out in a particular order and timing sequence. Several studies describe these sequences in detail [1,148,149,161,260,305].
Several studies report the effects of using fire in combination with other treatments to reduce reed canarygarss and are discussed in the Use of prescribed fire section.