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Tansy Ragwort Resurges In Oregon, But No Alarms Sounding

Tansy Ragwort Resurges In Oregon, But No Alarms Sounding

Tansy Ragwort, a noxious weed, kept in check via biocontrol.

Just like a year ago, western Oregon producers this summer are noticing   patches of the telltale bright yellow flowers of tansy ragwort, a noxious weed once the scourge of the '70s.

But Oregon Department of Agriculture weed watchers say there is no cause for alarm  as biological control agents should keep the plant from making an unwelcome comeback to prior levels of infestations.

"The cool, wet spring and early summer was good for tansy, not so good for out biocontrols," says Tim Butler, ODA Noxious Weed Control Program supervisor. "Even so, there is no reason to think we will return to what was taking place 30 or 40 years ago. It's all part of a natural cycle."

The equation is simple, he explains: as the tansy ragwort population grows, so do populations of flea beetles and cinnabar moths that feed on the weed. In the end, Butler believes the good insects will always maintain the upper  hand.

ODA continues to receive calls from landowners and neighbors anxious about the return of tansy, now in a very visible stage. The outbreaks are spotty and localized, observes Butler.

Nevertheless, many Oregonians remember the bad old days when tansy was so invasive in the west state that cattle and horse owners reported more than $4 million in losses each year as their animals grazed on infected pastures.

Too often, the leaves of tansy grew among the grasses consumed by livestock in the spring, leading to illness or death.

At this point in the growing season, tansy flowers are in bloom and the weed is tall enough for animals to generally avoid by eating around it.

"It's counterintuitive to jest let it go right now, but the whole premise of biological control is to allow the insects present to naturally build up on their own," says ODA Entomologist Eric Coombs.


Her has personally visited many of the sites were tansy is on the increase this year and has found the good bugs – the biocontrol agents that help kill the weed – present in all case.

This comes after intensive efforts years ago to release insects in infested areas where the flea beetle and cinnabar moth are now established as part of the natural environment.

For the second year in a row, a cool, wet spring has reduced the moth population. However, flea beetles are still active.

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