Wednesday, February 23, 2005
Curlyleaf Pondweed: Another Exotic Aquatic Plant in Minnesota
Source: MN Lakes
Eurasian watermilfoil made quite a splash in 1988 when it showed up for the first time in Minnesota in Lake Minnetonka. But another exotic plant invader in Minnesota beats milfoil by a mile-curlyleaf pondweed. It has been in Minnesota since the early 1900s, and it is documented to be present in over 500 lakes today. It does not cause problems in every lake it inhabits, but it can be a nuisance in lakes where it does well.
It has an alternative lifestyle
Curlyleaf pondweed (Potamogeton crispus) has several life cycle attributes that make it unique. Curlyleaf acts like a winter annual, although it is supposed to be a perennial. Nearly all other aquatic plants are perennials. Curlyleaf 's winter and spring growth spurt is one of its keys to success because there is very little competition from native plants at this time of the year.
Curlyleaf turions
In a typical year, curlyleaf pondweed sprouts from seed-like growths, called turions, in September through October. It will grow for a month or two until ice cover. Then growth slows down; the plant is just rest-ing. As soon as the ice goes off, curlyleaf growth explodes, and it can reach the lake's surface by mid-May. Typically, it's the first plant to make it to the lake surface and is the early summer nuisance on many lakes. After growing up, curlyleaf starts producing turions. Then, in late May or early June, a flower stalk grows above the water line signaling the end of its spring growth. After that point, the whole crop dies back and is often gone by mid-June. The turions lie on the lake bottom and the cycle starts again in September, when the turions sprout.
Why control is important
Curlyleaf pondweed has two ways to make conditions unpleasant in a lake. First, it can grow very dense, and when it reaches the surface, it creates a block of vegetation that is difficult for fish to swim through and boats to motor through. Stem densities have been recorded at up to 2,000 stems per square yard, making it a denser growing plant than Eurasian watermilfoil and nearly all other native plants.
The second unpleasant aspect of curlyleaf is the timing of its die-off. Native aquatic plants live through the growing season and die back in late summer and early fall when temperatures are cooler and the days are shorter. Nutrients from fall plants dying back go into bacterial growth rather than algae growth. However, curlyleaf has the peculiar distinction of dying back in early summer at the same time the algae population is growing rapidly and can readily take up the nutrients coming from the decomposing plants. Thus, the curlyleaf decomposition contributes to algae blooms.
If curlyleaf growth can be reduced, native plants should do better with less competition from curlyleaf, and recreational and ecological aspects of lake use will be enhanced.
There's hope: curlyleaf experiences from other lakes
Because of curlyleaf 's unique life cycle, harvesting and cutting approaches have to be implemented in late spring or early summer to get long-term curlyleaf control. Likewise, if herbicides are used, they have to be used early enough to kill the plant before turions are produced. Sometimes label restrictions prohibit early season herbicide use because water temperatures are too cold. Currently, herbicides have not been very effective, but this is an area of research.
About the author: Steve McComas, owner of Blue Water Science in St. Paul (651-690-9602), is an aquatic scientist, specializing in lake and watershed management. He is author of the book, Lake Smarts:The First Lake Maintenance Handbook, a do-it-yourself guide to solving lake problems that was developed in cooperation with the U.S. EPA's Clean Lakes Program. The 228-page book is available for $21.95 (includes shipping) from the Terrene Institute, 202-833-8317.
How curlyleaf pondweed control can reduce algae growth:
Work done by Blue Water Science, St. Paul, has found that there is 5.5 pounds of phosphorus in the plant tissue per acre of curlyleaf pondweed. The nearly 300 acres of curlyleaf pondweed in Bald Eagle Lake represent over 1,600 pounds of phosphorus that is released into Bald Eagle Lake when the curlyleaf plant dies back in mid-summer.
Eurasian watermilfoil made quite a splash in 1988 when it showed up for the first time in Minnesota in Lake Minnetonka. But another exotic plant invader in Minnesota beats milfoil by a mile-curlyleaf pondweed. It has been in Minnesota since the early 1900s, and it is documented to be present in over 500 lakes today. It does not cause problems in every lake it inhabits, but it can be a nuisance in lakes where it does well.
It has an alternative lifestyle
Curlyleaf pondweed (Potamogeton crispus) has several life cycle attributes that make it unique. Curlyleaf acts like a winter annual, although it is supposed to be a perennial. Nearly all other aquatic plants are perennials. Curlyleaf 's winter and spring growth spurt is one of its keys to success because there is very little competition from native plants at this time of the year.
Curlyleaf turions
In a typical year, curlyleaf pondweed sprouts from seed-like growths, called turions, in September through October. It will grow for a month or two until ice cover. Then growth slows down; the plant is just rest-ing. As soon as the ice goes off, curlyleaf growth explodes, and it can reach the lake's surface by mid-May. Typically, it's the first plant to make it to the lake surface and is the early summer nuisance on many lakes. After growing up, curlyleaf starts producing turions. Then, in late May or early June, a flower stalk grows above the water line signaling the end of its spring growth. After that point, the whole crop dies back and is often gone by mid-June. The turions lie on the lake bottom and the cycle starts again in September, when the turions sprout.
Why control is important
Curlyleaf pondweed has two ways to make conditions unpleasant in a lake. First, it can grow very dense, and when it reaches the surface, it creates a block of vegetation that is difficult for fish to swim through and boats to motor through. Stem densities have been recorded at up to 2,000 stems per square yard, making it a denser growing plant than Eurasian watermilfoil and nearly all other native plants.
The second unpleasant aspect of curlyleaf is the timing of its die-off. Native aquatic plants live through the growing season and die back in late summer and early fall when temperatures are cooler and the days are shorter. Nutrients from fall plants dying back go into bacterial growth rather than algae growth. However, curlyleaf has the peculiar distinction of dying back in early summer at the same time the algae population is growing rapidly and can readily take up the nutrients coming from the decomposing plants. Thus, the curlyleaf decomposition contributes to algae blooms.
If curlyleaf growth can be reduced, native plants should do better with less competition from curlyleaf, and recreational and ecological aspects of lake use will be enhanced.
There's hope: curlyleaf experiences from other lakes
Because of curlyleaf 's unique life cycle, harvesting and cutting approaches have to be implemented in late spring or early summer to get long-term curlyleaf control. Likewise, if herbicides are used, they have to be used early enough to kill the plant before turions are produced. Sometimes label restrictions prohibit early season herbicide use because water temperatures are too cold. Currently, herbicides have not been very effective, but this is an area of research.
About the author: Steve McComas, owner of Blue Water Science in St. Paul (651-690-9602), is an aquatic scientist, specializing in lake and watershed management. He is author of the book, Lake Smarts:The First Lake Maintenance Handbook, a do-it-yourself guide to solving lake problems that was developed in cooperation with the U.S. EPA's Clean Lakes Program. The 228-page book is available for $21.95 (includes shipping) from the Terrene Institute, 202-833-8317.
How curlyleaf pondweed control can reduce algae growth:
Work done by Blue Water Science, St. Paul, has found that there is 5.5 pounds of phosphorus in the plant tissue per acre of curlyleaf pondweed. The nearly 300 acres of curlyleaf pondweed in Bald Eagle Lake represent over 1,600 pounds of phosphorus that is released into Bald Eagle Lake when the curlyleaf plant dies back in mid-summer.
