Curly-leaf Pondweed (Potamogeton crispus) is an exotic submergent aquatic plant native to streams in Europe and Asia. It was first documented in Wisconsin in 1905, and is now found throughout much of the U.S. Unique growth characteristics allow curly-leaf pondweed to have a competitive advantage over native plants. While not as aggressive as Eurasian watermilfoil, curly-leaf pondweed can achieve nuisance densities that impede recreation, threaten lake ecology and decrease water quality.
Curly-leaf pondweed begins growing in late fall and will grow under the ice. By spring, the plant will have a head start over native species. By early summer, curly-leaf pondweed often forms dense mats that reach the surface. At this stage, the plants have formed a vegetative reproductive structure called a turion. By late summer, usually August, adult plants die-off and decay, leaving behind the turions. When waters cool again in fall, these turions germinate – repeating the life-cycle.
One benefit of curly-leaf pondweed is that it provides winter cover for fish. However, its early-season growth gives it a competitive advantage that often causes it to displace important native plants. A late-summer die-off then, can lead to a sudden loss of habitat for fish and invertebrates.
Dense beds of curly-leaf pondweed can clog boating lanes and inhibit traditional recreational uses, such as swimming, fishing, and sailing. Even waters that historically had limited plant growth due to high turbidity may develop nuisance levels of curly-leaf pondweed. The plant’s early-season growth often allows it to proliferate in lakes that may become too turbid for other species as the season progresses.
Dense plant beds may lead to stagnation, sediment accumulation and oxygen depletion. The greatest water quality impact of curly-leaf pondweed however, is caused by the plant’s massive die-off during the warmest time of year. The nutrient release from tons of rotting vegetation typically causes nuisance algae blooms and increased turbidity.
Herbicide treatments and mechanical harvesting are most often used to control the plant. However long-term control is difficult to achieve because turions survive and regenerate. Research conducted by the Army Corps of Engineers (ACOE) though, holds promise for providing long-term control of the plant. The ACOE recommends conducting early-season treatments – before turions form – using the herbicide endothall for up to three consecutive seasons. This allows the majority of turions in the lakebed to sprout, but treatments kill plants before new turions can grow. Cason & Associates biologists have found this to be an effective long-term strategy on lakes where all of the curly-leaf pondweed can be targeted. Call or email today for more information.