Tansy ragwort doesn't look so bad, with its clusters of yellow, daisy-like flowers.

But Langley environmentalists are trying to keep an eye on its spread, and to warn property owners about its presence.

On Tuesday morning, Lisa Dreves of the Langley Environmental Partners Society (LEPS) and volunteer Bill Kippan of the Little Campbell Watershed Society were out mapping clusters of the weed.

An invasive species from Europe, tansy ragwort is most dangerous to grazing animals.

The plant is toxic to horses and cattle, but does not cause instant illness or death. Instead, it causes slow, irreversible liver damage. Over time, that can cause symptoms in animals such as depression, loss of appetite, aimless wandering, and a photosensitive skin reaction.

The ragwort can be seen often in ditches and recently grazed fields.

It is common throughout the southwest corner of B.C., including in Langley.

The growing conditions of this spring and summer seem to have been pretty good for tansy ragwort, noted Dreves.

"It seems to have been really successful this year, unfortunately," she said.

LEPS is advising farmers to be vigilant for the weed and to cut it back whenever they find it on their property.

Even those without livestock can help. The drifting seeds of tansy ragwort can easily float across property lines.

LEPS, meanwhile, is working with the Township to slow its spread through ditches. The mapping Kippan and Dreves were doing will be handed over to the Township, and LEPS will recommend times when mowing or dredging in ditches will be most effective in killing or controlling tansy ragwort, along with its fellow invasive species Himalayan balsam, Japanese knotweed, and purple loosestrife.

LEPS and its volunteers aren't pulling out too many of the plants one at a time.

"There's way too much of it to hand pull," said Kippan.

The mapping efforts are part of ongoing projects by LEPS to map out a wide variety of invasive plant species in the Langleys.

mclaxton@langleyadvance.com