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Curly-Leaf Pondweed

In the spring of 2003, some residents on the lake noticed the proliferation of a noxious exotic aquatic weed (unlike favorable vegetation that provides habitat for fish and filters pollutants), called Curly-Leaf Pondweed.

"Backwards" Growth Pattern

Curly-Leaf Pondweed has an unusual life cycle, as it grows underneath the ice and actually prefers cooler water. This gives it a "head start" over other exotics.

Plants form in dense mats, inhibiting recreation. The plant produces a "turion," a hardened plant stem, flowers, then promptly dies off by mid-late June.

Curly-Leaf Pondweed identification sheet (PDF, 1.2 MB).

The dead plants can pile up on shore and increase phosphorus concentrations in the lake, in turn increasing the instance of algal blooms.

The turions lie dormant during the remainder of the summer while other native plants are growing, then germinate in the fall when other plants are dying back.

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Similar to Eurasian Milfoil, if left unchecked, it will choke out a lake, making it undesirable to live on and lowering property values. Also like milfoil, it can spread from plant fragments. It is therefore vital that watercraft owners clean their craft off after using an infested lake and before entering another one.

Controlling the weed

In October 2003, the Water Quality Task Force met with representatives of the DNR Exotic Species Control, Fisheries, and Hydrology departments. According to the DNR, there are three ways to control it:

  • Spot application of herbicides.
  • Mechanical harvesting, either with equipment or hand-pulling and disposal away from the lake and shore.
  • Drawdown of the water to dry, freeze and kill the roots.

After discussing the issue with the DNR, city officials and other lake associations, the third method was deemed the least costly and most effective in the short term.

The lake was lowered to 4 feet starting on November 3rd and refilling began December 8th.

In the spring of 2004, the DNR spot-checked areas of the lake to determine the success of the drawdown. The drawdown appeared to make great inroads, however there were still spots where it proliferated in depths beyond the 4'.

The weed has been continued to be monitored, however because of its spottiness and concern for wildlife the DNR has not since recommended a drawdown. See 2006 map (PDF, 1.7 meg).

Residents are encouraged to pull the weed if they see it in the spring and destroy the plant away from the lake (do not compost it). The Lake Orono Water Quality Committee is working on a plan to address curly-leaf in public areas and for those who are physically unable to pull the weed.

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