By San Juan County Noxious Weed Board

Special to the Weekly

It is tansy ragwort season again, one of the county’s worst weeds, and the plants are beginning to flower along roadsides, in fields and in residents’ yards.

Highly toxic, its alkaloids are present in all plant parts. Cattle, horses and goats consuming either growing plants or tansy ragwort in silage and hay store these poisons in their liver (Jacobs, J. 2009 USDA- NRCS).

Even if symptoms are not noticeable, or appear minor, the cumulative toxins cause irreversible liver damage resulting in reduced weight and, possibly, sudden death in previously healthy animals. Tainted dairy milk can have an off-taste, and contaminated pollen may make honey unpalatable.

Tansy is best controlled by pulling the entire plant out of the ground, but it is critical to remove the flower heads – if present– before discarding the rest of the plant. These heads should be bagged and taken to the solid waste facility, where they may be disposed of at no charge. If the heads are left on the plant, the seeds will mature and re-infect the area which is being cleared. This is especially important along roadsides where the flower heads and developing seeds can be picked up by tires and dispersed over great distances. Please remember to wear gloves when handling this toxic plant.

You may see black and orange/yellow-striped caterpillars of the cinnabar moth eating the leaves and flowers on some plants. If there are only a few found on the plant we usually pull the plant and shake them off onto nearby tansy rosettes. If numerous caterpillars are defoliating the plants, we usually leave them alone. When ready to pupate, they leave their host plant, but, unfortunately, the plants can re-flower and set seed even if completely defoliated.

For info, call at 376-3499.