Sulfur cinquefoil (Potentilla recta L.) is a perennial forb native to Eurasia. It first appeared in North America before 1900 in Ontario, Canada. By the 1950s it was widely established in eastern Canada, the Pacific Northwest, northeastern United States and the Great Lakes region. In 2017 sulfur cinquefoil was reported in the 48 contiguous states in the United States (Figure 1), and southern Canadian provinces.
Sulfur cinquefoil is a long-lived perennial (30 years or more) with a woody taproot. New shoots grow from the root perimeter; however, plants do not have rhizomes. Each plant has one to several erect stems about 1 to 2 feet in height. Leaves have 5 to 7 leaflets arranged in a palmate pattern (Figure 2) and are basal until the plant sends up flowering stalks in spring. Numerous leaves are attached along the length of the stem with fewer leaves near the base. Stems and leafstalks are covered with hairs that are ¼ inch in length and project outward at right angles (Figure 3).
Flowering begins in late May (Figure 4) and may continue throughout the summer if growing conditions are favorable. Sulfur cinquefoil reproduces only by seed with a single plant capable of producing up to 1,650 seeds per year.
SPREAD AND IMPACTS
Sulfur cinquefoil is adapted to a wide range of environmental conditions. The plant is found in grasslands, shrub and open forest habitat types, and disturbed areas. Seeds are likely spread by humans, vehicles, and animals including wildlife and domestic livestock. Movement of contaminated equipment for agricultural purposes, construction, and fire suppression activities hasten seed spread. Seeds that fall directly from the parent plant disperse only a short distance unless aided by an external vector as described above.
Sulfur cinquefoil has a high tannin content limiting its palatability to most livestock and wildlife. Studies conducted in Montana indicated utilization by livestock and wildlife was less than 1 percent on 98 percent of sites sampled. Selection of plants other than sulfur cinquefoil by grazing animals may have a long-term impact by reducing bio-diversity. Sulfur cinquefoil reduces grass production by about 60 percent as a result of direct plant competition.
Field studies conducted on sulfur cinquefoil in the United States and Canada show that Milestone® specialty herbicide at 4 to 7 fluid ounces per acre (fl oz/A) provided good to excellent control (90 to 100%) one year following application. The addition of 2,4-D to Milestone did not improve control over Milestone applied alone (Figure 5).
The optimum time to apply Milestone to control sulfur cinquefoil and stop seed production is at rosette to early bolt stage in spring. Sulfur cinquefoil is often difficult to locate until the plant blooms; thus, the higher application rate will be more effective on mature plants treated later in the summer.
Hand pulling, grubbing, or hoeing may be used to control small populations of sulfur cinquefoil. These methods can cause significant disturbance and sites should be seeded with desirable species to reduce reinvasion by sulfur cinquefoil germinating from seed. The caudex (basal stem structure) must be removed to effectively control the plant. Follow-up treatment will be needed if plants have produced seed.
Mowing prior to bloom will reduce flowering and seed production but will not reduce plant populations. Sulfur cinquefoil is not usually a problem in cultivated cropland; however, tillage will control sulfur cinquefoil on cropland. Follow-up management using herbicides may be needed to control re-generating plants. Mowing and tillage equipment must be cleaned of soil that may contain seed or plant root crowns to prevent spread to non-infested sites.
Prescribed fire alone will not control sulfur cinquefoil and may increase cinquefoil populations unless control measures such as herbicide treatments are applied post-burn. Field studies in Montana indicate spring and fall prescribed fires did not change sulfur cinquefoil population densities five years post-burn compared to infestations that were not burned. Fires on infested sites that do not have competitive plants may increase the invasiveness of sulfur cinquefoil.
Most livestock avoid grazing sulfur cinquefoil due to the high tannin content. Confining sheep or goats on an infestation may reduce seed production. Proper grazing management is essential to maintain the health and competitiveness of desirable pasture and rangeland plant communities. This will help slow invasion and increase effectiveness of other control treatments.
There are no biological control agents currently available for management of sulfur cinquefoil. The probability of agents becoming available in the near future is not likely because of the many native and agricultural plants that are close taxonomic relatives. A rust fungus (Phragmidium ivesiae) infects sulfur cinquefoil in the northern Rocky Mountain region; however, its effectiveness is limited.
Long-term effective management of sulfur cinquefoil is unlikely in areas where desirable plant species are absent, such as disturbed areas or those dominated by annual grasses. Restoring desirable plant species and communities that resist weed invasion should be considered an integral component of the management program. Recommendations for desirable species adapted to a specific area can be obtained from state universities, cooperative extension service, Natural Resource Conservation Service, and private conservation organizations such as Pheasants Forever.
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Active ingredients for herbicide products mentioned in this article: Milestone (aminopyralid); Escort (metsulfuron methyl)