NW Environmental News: Deadly plant makes a comeback; other invasives; research

tansy.JPGView full sizeCool weather has revived deadly tansy ragwort, which can kill cows and horses.
Oregon State University researchers warn that tansy ragwort, an invasive weed that can kill horses and cattle if they eat it, is flourishing in western Oregon this summer after nearly three decades of effective control.

A La Niña weather pattern and the cool wet spring provided excellent growing conditions for tansy while knocking down insects that feed on it and have largely kept it under control since the 1980s, according to an OSU news release.

Tansy ragwort is a member of the sunflower family and was introduced into Oregon in the 1920s. It contains toxins that can kill grazing cows and horses, however, or cause spontaneous abortions in pregnant animals.

In 1960, the Oregon Department of Agriculture introduced insects that feed on the plant: the cinnabar moth, tansy ragwort flea beetle and a seed head fly. The department distributed the insects throughout the state, and by the 1980s they had tansy under control.

Pacific Northwest Extension: Tansy Ragwort

Introducing plants from elsewhere often leads to regrets. In February 2010, Oregon took action against plants that can smother native species.

The Oregonian: Oregon bans sale of English ivy, butterfly bushes

Here's a list of the state's worst invasive plants, animals and organisms.

Oregon Invasive Species Council: 100 most dangerous invaders to keep out

--Eric Mortenson