More info for the terms: cover, fire management, frequency, invasive species, natural, nonnative species, presence, restoration, root crown, rootstock, severity, succession
Impacts: Explicit in the definition of sulfur cinquefoil as a problem species is the assumption that it displaces other plant species and the myriad organisms that depend on these plant communities, as well as the negative economic consequences for industries based on these natural resources. Sulfur cinquefoil may have harmful impacts on native flora and fauna, however more research is needed to clarify the extent of these impacts [60]. Untested hypotheses and unsubstantiated claims can be perpetuated in the literature until they become widely accepted, without the benefit of experimental analysis or peer review. A well-documented example of this occurred with purple loosestrife [32].
The following information on impacts of sulfur cinquefoil, its ability to outcompete native and other nonnative plants, and its rapid rate of expansion are commonly found in agricultural extension and gray literature though they are largely untested. To better define its potential impacts, research is needed on the competitiveness of sulfur cinquefoil relative to other plant species, its rate of expansion, its persistence at various seral stages in different ecosystems, its ecological amplitude, and its influence on the dynamics of various ecosystems [60].
There are no specific data on the relative competitiveness of sulfur cinquefoil. Its perennial nature and large root reserves likely give it a competitive advantage in open-canopied situations, but the relative advantage of these attributes remain unquantified [60]. According to Rice and others [66,68] sulfur cinquefoil displaces native plant species in undisturbed habitats, reduces grass production, and may alter the functioning of ecosystems by lowering biodiversity, although this is not documented quantitatively.
Based on canopy cover estimates of sulfur cinquefoil at 85 sites in western Montana, Rice [70] concludes that "sulfur cinquefoil often becomes a significant component of the plant community, and has proceeded to dominance on many sites" [69]. At 75% of the 85 sampled sites, sulfur cinquefoil canopy cover exceeded 5% of the plant cover; on 50% of the sites, sulfur cinquefoil canopy cover exceeded 15%; on 14% of the sites, sulfur cinquefoil canopy cover was 50% or more; and on 1 site, sulfur cinquefoil canopy cover was 75%. On most sites sulfur cinquefoil canopy cover ranged from 5 to 15% [69]. While Rice [69] suggests that canopy cover is a useful measure of the severity of a weed infestation and the competitive ability a particular plant, Lesica [50] indicates that canopy cover estimates are subjective and can be dependent on yearly climatic fluctuations, and not, therefore, very useful for monitoring trends in plant communities.
Rice also suggests that sulfur cinquefoil competes well with other nonnative, invasive species such as yellow starthistle, leafy spurge, and spotted knapweed, although no quantitative evidence is given [69,70]. Land managers in Montana indicate that sulfur cinquefoil displaces spotted knapweed on several sites [37,69]. The management history of these sites is unknown, and may influence the relationship between sulfur cinquefoil and spotted knapweed. For example, if clopyralid is used to control spotted knapweed, sulfur cinquefoil would be favored since sulfur cinquefoil is not sensitive to clopyralid [46,70]. Similarly, sulfur cinquefoil may be displacing diffuse knapweed on sites in British Columbia where knapweed vigor is reduced by introduced biological control agents [60].
In 1981, Forcella and Harvey [22] plotted the number of counties reporting the presence of each of 100 nonnative plant species in Washington, Oregon, Idaho, Montana, and Wyoming over time and described 3 patterns of infestation. They described infestation by sulfur cinquefoil as following an "exponential pattern." The distribution of sulfur cinquefoil was rapidly increasing as of 1980, and they predicted that it would become a problem in western Montana, eastern Washington and central Idaho "at some later date" [22]. According to Rice [70] "sulfur cinquefoil is rapidly increasing its geographic distribution. The number of new colonies is increasing exponentially. Many of these infestations are reaching environmentally severe sizes and densities." These assessments, however, remain neither confirmed nor denied by experimental data [60].
While it has been suggested that sulfur cinquefoil infestations can expand rapidly, and large infestations are not uncommon, the majority of colonies of sulfur cinquefoil observed in western Montana were small, with half of them less than 10 acres (4ha) [69,70].
The influence and interaction of sulfur cinquefoil with chemical and biological soil processes are also largely unknown. As a pioneer species on disturbed soil, it may help to bind soil and prevent erosion [60,91]. The breakdown of annual growth and root exudates likely releases tannins into the soil, but their influence on soil ecology and water quality have not been examined. Sulfur cinquefoil is not known to be allelopathic, and its interactions with soil biota also remain unquantified [60].
Control: Correct identification is an important first step in controlling sulfur cinquefoil, as it may be easily mistaken for native cinquefoils (see General Botanical Characteristics).
Prevention of sulfur cinquefoil establishment by maintaining native plant communities in an undisturbed condition is the most effective control strategy. Monitoring, early detection and eradication of newly established plants before seeds are produced and populations expand is more efficient and effective than laboring to control established infestations. Individual plants and small patches of sulfur cinquefoil can be eliminated by hand-pulling or digging, or by spot spraying of herbicides. The root crown (upper portion of the root system) must be removed or killed so that plants cannot resprout.
Because sulfur cinquefoil seeds may remain viable in the soil for 3 years or more [66], treated sites must be monitored annually for newly established sulfur cinquefoil plants [70].
Because sulfur cinquefoil occurs and is competitive with several other invasive species [69], management to control it and/or other species must consider the possibility of succession to other undesirable species when plants are removed.
Prevention: Preventing sulfur cinquefoil infestations is the most time- and cost-effective management approach. This is accomplished by maintaining desirable plant communities (by limiting livestock grazing, minimizing soil disturbance, and seeding disturbed sites with desirable species), preventing sulfur cinquefoil seeds from entering uninfested areas, and careful monitoring for and early eradication of newly established sulfur cinquefoil plants. This is especially important where sulfur cinquefoil is common in areas around the management site, especially along roads, trails, and rivers.
Prevent sulfur cinquefoil seeds from entering uninfested areas as follows:
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Check and clean equipment before moving it into infested areas or before bringing it from infested areas.
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When moving livestock from infested to uninfested areas, hold them in corrals or small pastures until viable seeds have had time to pass through the digestive tract (6 days for cattle, 11 days for sheep).
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Monitor for sulfur cinquefoil seedling establishment in livestock holding areas and areas where dirt has been imported [48].
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Avoid purchasing feed or seed that could be contaminated with weed seeds. Viable sulfur cinquefoil seeds may even be present in feed pellets.
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Treat road construction projects as 10- to 20-year biological projects rather than 1- to 2-year engineering projects, with biologists and resource managers overseeing road construction and restoration. Projects should not be considered complete until native vegetation is fully established. Topsoil removed during construction can be redeposited in roadside ditches, and roadsides reseeded with native species. Roadsides should then be regularly monitored and actively managed for control and eradication of nonnative species [84].
Integrated management: While there is no specific information on integrated management of sulfur cinquefoil, a combination of control methods is often necessary to eradicate or successfully contain infestations of nonnative invasive plants. Managers are encouraged to integrate different control methods that can complement one another in a given situation. Integrated management includes considerations of not only killing the target plant, but also of establishing desirable species and discouraging nonnative, invasive species over the long-term.
Physical/mechanical: Hand-digging or hand-pulling sulfur cinquefoil plants can be effective in small infestations, but may be impractical for large infestations, since the entire root crown must be removed in order to kill the plant [60,70]. Annual monitoring must be conducted to locate new plants that may establish from the soil seed bank or from seed dispersed from off-site sources.
Mowing is not effective for controlling sulfur cinquefoil. It responds by developing heavier, horizontally spreading roots and increasing vegetation near ground level [70,91]. In Michigan, the mean dry weight of roots was much greater in plants growing in a mown strip (4.2 g per plant) than from plants in the adjacent undisturbed field (2.0 g per plant) [91].
Sulfur cinquefoil can be controlled by plowing and planting to a clean-cultivated crop [91]. In a sulfur cinquefoil-infested field in Michigan plowed in May, seedlings of sulfur cinquefoil were numerous by mid-June, as well as plants emerging from old rootstock [91]. Discing and reseeding to grass at a site in British Columbia resulted in complete control of sulfur cinquefoil. This, of course, cannot be applied over grassland and forest ecosystems that are managed in their natural state [60].
Fire: See Fire Management Considerations.
Biological: Biological control of invasive species has a long history, and there are many important considerations to be made before the implementation of a biological control program. The reader is referred to other sources (e.g. [65,92]) and the Weed Control Methods Handbook [83] for background information on biological control. Additionally, Cornell University, Texas A & M University, and NAPIS websites offer information on biological control.
There are currently no biological control agents available for sulfur cinquefoil, although a number of insects and fungi are associated with sulfur cinquefoil. A field survey in Eurasia identified 26 phytophagous insect species associated with sulfur cinquefoil in its native range [76]. A survey in the northeastern U.S. identified 47 species of phytophagous insects and pollinators on sulfur cinquefoil; among them are the strawberry root weevil and the strawberry aphid [8]. A rust fungus was found on sulfur cinquefoil at 79% of sampled sites in Montana. Root and crown boring insects were also collected from sulfur cinquefoil plants on numerous sites, and 6 species were isolated from these collections. Three of the identified species are known to be pests on strawberry (Fragaria spp.) [69]. The rust fungus is also known to occur on several of the sulfur cinquefoil populations in British Columbia. Three plant diseases have also been associated with sulfur cinquefoil populations in British Columbia [60].
A biological control program using insects against sulfur cinquefoil would be difficult due to the close genetic relationship between strawberries and cinquefoils, and probable attractiveness of strawberry to phytophagous insects that attack Potentilla [8]. Based on this close relationship, Batra [8] concludes that initiation of a biological control program for sulfur cinquefoil is not highly recommended. Additionally, a potential biocontrol agent must also be benign to (or incapable of occupying the habitats of) about 70 species of Potentilla with more than 80 subspecies and varieties that are found in North America [60]. Given the close relationship between sulfur cinquefoil and other Potentilla and Fragaria species, and the large number of native and introduced plants that must be screened, the search for a suitable biological control could be the longest and most costly in the history of North America [60].
Nonetheless, by 1996, 2 potential biological control agents were targeted for screening, a root moth (Tinthia myrmosaeformis) and a seed head weevil (Anthonomus rubripes) [67]. Field releases of any such insects would occur a decade or more in the future [70].
Sulfur cinquefoil is unpalatable to most livestock. Goats are the only animals that have been reported to select for sulfur cinquefoil [70]. Intensive grazing systems can increase sulfur cinquefoil utilization to about 5%, but sulfur cinquefoil appears to be one of the last plants selected [69,70].
Chemical: Herbicides are effective in gaining initial control of a new invasion (of small size) or a severe infestation, but are rarely a complete or long-term solution to invasive species management [12]. Herbicides are more effective on large infestations when incorporated into long-term management plans that include replacement of weeds with desirable species, careful land use management, and prevention of new infestations. Control with herbicides is temporary, as it does not change conditions that allow infestations to occur (e.g. [95]). See the Weed Control Methods Handbook [83] for considerations on the use of herbicides in natural areas and detailed information on specific chemicals.
Dicamba and clopyralid do not effectively control sulfur cinquefoil [66,70]. Picloram (applied in fall or spring), 2,4-D ester (applied in spring at rosette through bud stage), or a mix of dicamba and 2,4-D amine (applied at the rosette stage), are each effective at controlling sulfur cinquefoil. 2,4-D ester is suggested where potential water contamination is a consideration. On dryland sites, picloram may be preferred because its residual activity can suppress re-establishment from seeds in the soil seed bank [70], but it is still necessary to conduct appraisal surveys of treated sites in subsequent years, and plan systematic retreatments if eradication is the management goal [69].
Because sulfur cinquefoil is not sensitive to clopyralid [46], application of clopyralid to mixed stands of sulfur cinquefoil and spotted knapweed will depress the spotted knapweed without harming sulfur cinquefoil, thereby giving sulfur cinquefoil the competitive advantage [70].
Cultural: Because sulfur cinquefoil is intolerant of complete shade, land management practices that allow other vegetation to increase in cover, and therefore contribute to a concomitant decline in sulfur cinquefoil, should be promoted. Grazing should be managed with appropriate timing, intensity, frequency, and duration to leave adequate desirable vegetation. Soils disturbed by logging, construction, or other management activities should be revegetated as soon as possible with desirable species [60].