Help! Tansy is getting the upper hand.

Tansy Ragwort with Cinnabar moth
Photo credit: Ken Kingsley

Where can I get some of the tansy flea beetles ? We used these many years ago and they did an incredible job. I do have some of the cinnabar larva present but they never start working early enough to prevent the plants from going to seed. The neighboring property has an enormous tansy crop and I am losing ground to this plant in my pasture.

- Coos County, Oregon

I am not aware of any commercially available flea beetles. Below is some information we have compiled regarding the tansy situation this year.

· There is more tansy ragwort than usual this year, most likely caused by the cold, wet April and May, which undermined established biological controls such as the cinnabar moth and flea beetle. Both insects are extremely effective at curbing the highly destructive weed that’s poisonous to livestock. The insects are still here, but their population is reduced.

· The cinnabar moth and flea beetle work in a cycle with the plant. When the insects have reduced the amount of tansy ragwort there is less for them to feed on and their populations decline. As the weed establishes again, the amount of insects increases. That can take several years, however.

· At one time, the Oregon Department of Agriculture was distributing the cinnabar moth to the public, but currently has no plans to do that.

· Tansy ragwort is poisonous to livestock, except sheep and goats. Animals that have eaten tansy may quit eating and drinking, start to wander and appear listless. Often, they will lie down and are too weak to get up. Eventually, tansy poisoning will kill the animal. Currently, there is no treatment.

· To help control tansy ragwort:

· Don’t overgraze pastures. The best defense against tansy ragwort is a strong stand of grass.

· Now is not the time to spray. It should be done in spring before the plant bolts, or in fall when new seedlings are still rosettes.

· Mowing pastures after seeds have matured on the plant is not recommended because the seeds can spread – and they can live in the soil for as long as 10 years and then germinate. Mowing can cause the plants to become short-lived perennials and grow back the following year. It also limits the food source for the biocontrol insects.

· If the acreage is small, the weed can be dug out and burned, buried, or sealed and taken to a landfill. Composting generally doesn’t work because the average compost pile doesn’t get hot enough to kill the weed seeds.

Here is more information on Tansy control.

Andrew Hulting
Extension Weed Management Specialist
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