Sulfur cinquefoil is an invasive, perennial forb on rangelands of western Canada and the United States. Sulfur cinquefoil reproduces solely by seed and it is a prolific seed producer. Our 2-yr study (2006, 2007) investigated the optimal timing and intensity of defoliation to decrease aboveground productivity and seed production of sulfur cinquefoil plants on foothill rangeland in southwestern Montana. Each year, 150 sulfur cinquefoil plants within a 430-m2 enclosure were tagged for identification and randomly assigned to one of 15 clipping treatments with 10 plants per treatment. Clipping treatments were conducted at three timings: (preflower [early June], flowering [late June], and seedset [mid-July]) and all possible combinations of timings for a total of seven timing treatments clipped to two stubble heights (7.5 cm or 15 cm), comprising 14 unique treatments. The final (15th) treatment consisted of an unclipped control. Response variables collected at senescence (late July) included aboveground biomass; number of buds, flowers and fruits on each plant; and number and viability of seeds produced. Results indicated that defoliation of sulfur cinquefoil can effectively reduce its yield and seed production. All clipping treatments reduced aboveground biomass of sulfur cinquefoil compared with control plants (P ≤ 0.05), except clipping to 15 cm during preflowering in the wetter year of 2006. Clipping to either 7.5 cm or 15 cm at all times or combinations of timings reduced the number of buds, flowers, fruits, and seeds produced by sulfur cinquefoil (P ≤ 0.05). Viable seed production was reduced 99 to 100% when plants were clipped once to either 7.5 or 15 cm during flowering or seedset. Results suggest that targeted livestock grazing or mowing applied one time per season during flowering or seedset could effectively suppress the biomass production and viable seed production of sulfur cinquefoil.
Nomenclature: Sulfur cinquefoil, Potentilla recta L. PTLRC
Management Implications: Sulfur cinquefoil is a nonnative, perennial, invasive weed that currently infests thousands of acres of rangeland and abandoned cropland in the western United States and Canada. This plant is a concern because it produces thousands of seeds and is capable of invading undisturbed rangeland. There are no approved biological controls, and herbicide treatment is expensive; therefore, we evaluated the potential for defoliation to reduce yield and seed production of sulfur cinquefoil. Hand-clipping treatments were applied at 14 different timing and intensity combinations to determine those most appropriate to suppress sulfur cinquefoil. Overall, clipped plants produced ∼ 80% less aboveground forage and > 90% fewer viable seeds than control plants. Clipping applied when sulfur cinquefoil plants were flowering or in early seedset had the greatest impact on forage and seed production. Plants clipped one time to either a 15- or 7.5-cm stubble height at flower or later were unable to produce any viable seed during the current growing season. Multiple defoliations were not necessary to decrease seed production if the first defoliation occurred at the flower stage or later. The intensity of the defoliation did not matter so long as the fruits were removed from the plant. Because of the longevity and abundant seed production of the plant, areas infested with sulfur cinquefoil likely have a large soil seed bank, and multiple years of uniform defoliation will be necessary before any noticeable change in the existing population can be determined. However, defoliation holds potential to reduce the competitive ability of sulfur cinquefoil as well as the ability of the plant to add to the seed bank. Targeted livestock grazing or mowing are two potential ways to defoliate sulfur cinquefoil at the appropriate timing and intensity to suppress the plant