The summer of 2018 brought to light an increasing problem in Stillwater County in the form of a horrible pale-yellow flower. Sulfur cinquefoil, Potentilla recta, (Montana Statewide Noxious Weed Awareness and Education Program, Montana State University, Bugwood.org) is considered a Priority 2B noxious weed in Montana, meaning is abundant and widespread in many counties. Ecology & Management of Sulfur Cinquefoil (Montana NRCS Tech Note 17) describes it as a perennial forb from the Mediterranean region, first collected in Montana in 1947. It can be found invading native rangeland, shrubland, seasonal wetland, and open-forest sites, and is commonly found in disturbed or abandoned areas and roadsides. A study of 85 infestations in Montana revealed it to be found on all soil types except silt and it is often associated along with spotted knapweed.
Sulfur cinquefoil has a large taproot with a woody persistent stem base (caudex) that stores energy and fibrous, spreading lateral roots. Basal and stem leaves are palmately compound with 5-7 toothed leaflets. Pale to sulfur-yellow colored flowers are ½ to 1 inch in diameter and have five petals that are deeply notched. Stems have long hairs (up to ¼ inch) that are at right angles. The forb grows 1-2 feet tall, may live on average 3.5 years, however, a study in Oregon suggests individual plants could potentially live 20 or more years. Sulfur cinquefoil can produce at least 1,600 seeds per year, with some estimates being as high as 6,000 seeds per year. Seeds are thought to be viable for three years and most are dispersed within 2 feet of the parent plant. Light stimulates germination, and competition from other plants will reduce seedling germination and survival.
According to the Montana Field Guide, over 30 native cinquefoils can be found in Montana. There are three native species in the state that can be confused with sulfur cinquefoil, the most common one being northwest or slender cinquefoil (Potentilla gracilis). Unlike sulfur cinquefoil, this native forb rarely forms dense patches and is an important component of native plant communities. The achenes (seeds) of sulfur cinquefoil are small, dark brown, and comma shaped with a net-like pattern of veins. Slender cinquefoil seeds are similar in shape but are light brown color and smooth. Stem hairs on slender cinquefoil are flattened and one length, and basal leaves are more abundant and still present at flowering.
Management and eradication of an established infestation of sulfur cinquefoil is difficult. There no biological controls for managing sulfur cinquefoil as there are too many close native species and agriculturally important relatives, such as strawberries. Mowing can prevent it from going to seed, however, mowing alone will not decrease plant populations unless repeated often because large root reserves enable the plant to regrow rapidly. New infestations can be hand pulled and hoed or grubbed, but care must be taken to remove the caudex as it has regenerative buds. Sulfur cinquefoil is high in tannins, making it generally unpalatable to livestock. However, a research report from Montana State University Extension indicated that targeted grazing sheep on sulfur cinquefoil infestations in late June or mid-July can be a potential management option. With the sheep’s diet consisting of approximately 45-49% sulfur cinquefoil, they were able to achieve heavy use on the sulfur cinquefoil while maintaining a light to moderate use on the desirable perennial grasses and forbs. Grazing reduced viable seed production by 95-97%, so it may be possible to, over time, decrease and eliminate sulfur cinquefoil with targeted grazing if desirable species are not over-grazed and can continue to compete for light and resources with the noxious weed. Herbicide application can also be effective when used appropriately, contact your local county weed district with questions on recommended chemicals and timing of application. It may be beneficial to reseed an area after a chemical application to help reestablish desirable species in place of sulfur cinquefoil. As always, it is important to practice good grazing management so that grasses and forbs are strong and can compete with invading noxious weeds like sulfur cinquefoil.
Don’t be part of the problem, educate yourself and others on noxious weeds, how to identify them, how they spread, and how to control them. If you find an infestation on public land, report it immediately. Do your part to prevent the spread of noxious weeds on public and private lands for the benefit of everyone who lives, works, and recreates in our beautiful state.
Soil Conservationist, Columbus Field Office
References: *Ecology & Management of Sulfur Cinquefoil (Potentilla recta L.) NRCS Tech Note 2007 MT-17; *Montana Weed Control Association, https://www.mtweed.org/; *Slender Cinquefoil. NRCS Plant Fact Sheet, https://plants.usda.gov/factsheet/pdf/fs_pogr9.pdf; *Montana Field Guide, http://fieldguide.mt.gov/search.aspx; *Can Targeted Sheep Grazing Suppress Sulfur Cinquefoil? J.C. Mosley, R.A. Frost, B.L. Roeder, and R.W Kott. Department of Animal and Range Sciences, Montana State University Bozeman, MT and Teton County Extension, Choteau, MT.