Halifax council wants to use herbicide on invasive plant in Little Albro Lake

Halifax regional council will be seeking permission to use a selective herbicide to control an invasive plant in Little Albro Lake in Dartmouth, N.S., after a 2021 pilot project using benthic mats, also known as weed mats, did not yield optimal results.

The mats are a blanket-like barrier made out of synthetic or natural materials that can be placed on a lake bottom to block sunlight from the plant to control growth.

Yellow floating heart, which is native to East Asia and the Mediterranean, has been affecting the lake since 2006 and making it unusable for recreational purposes. 

In raising the motion at the environment and sustainability committee, Sam Austin, councillor for district 5, tried to put a positive spin on the failure of the pilot project, saying he was "excited " that the council was engaged in primary science. 

"Actually we have followed quite a process to try and identify what what works here in Halifax," Austin said. "I get a little bit of a thrill out of that. I support the recommendation."

Elizabeth Montgomery, a water resource specialist, told the committee that permission would be sought to use the herbicide ProcellaCOR for one year. She said if it extended past a year, council would have to reapply and justify their request.

According to Montgomery, the small size of the lake would likely only require one application of the herbicide early in the season, with manual control of the plant after that.

There was a good chance Heath Canada would approve the use, Montgomery said, but if not, they would have to reevaluate and consider other options. 

Asked by Austin if there was any thought given to recolonizing the lake with native species, Montgomery said it was something they were considering.

"If you just empty this pond out and don't plant anything back in,  we just are opening it up to other invasive plants or the resurgence of this plant or blue green algae or other types of pond weed," she said.

"We would be looking to focus on native species in line with the naturalization strategy."

The motion, which passed unanimously, calls on council to direct the chief administrative officer to seek approval from federal and provincial authorities to use the herbicide on the lake. 

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