Common tansy (Tanacetum vulgare)

Introduction:

Known as golden buttons and garden tansy, is a perennial herb in the sunflower family. This species, native to Europe, has a long history of medicinal use. It was first introduced to North America for use in folk remedies and as an ornamental plant. The plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of livestock poisoning are rare, though, because tansy is unpalatable to grazing animals. Human consumption of common tansy has been practiced for centuries with few ill effects, yet the toxic properties of the plants are cumulative and long term consumption of large quantities has caused convulsions and even death. In addition, hand pulling of common tansy has been reported to cause illness, suggesting toxins may be absorbed through unprotected skin. Common tansy is an invader of disturbed sites and is commonly found on roadsides, fence rows, pastures, stream banks and waste areas throughout North America. It may threaten the ecological health of these areas through reduction in livestock forage, wildlife habitat and species diversity. Common tansy is listed as a noxious weed in Montana.

Identification:

Mature common tansy plants are easily recognized by the flat-topped clusters of small, button-like, yellow flowers they bear in the summer. Common tansy is often confused with tansy ragwort (senecio jacobea), a poisonous pasture weed and statewide noxious weed. Tansy ragwort can be distinguished from common tansy by its ray flowers (petals), absence of sharp toothed leaves and the long fringe of soft white hairs found on the seeds.

Distribution:

By the 1800s this weed was growing wild throughout the Northeast. In 1912, common tansy was reported as far west as Kansas and it was widespread in California by 1952. This weed was first documented in Montana in 1936 in Silver Bow County. Common tansy now occupies fences, roadsides, ditch banks and other disturbed areas throughout temperate regions of North America. In Montana it tolerates a wide range of precipitation and temperature zones, giving it the potential to occupy almost every county in the state.

Biology:

Common tansy spreads mainly by seeds, and less commonly from creeping rhizomes, to form dense clumps of stems. Each stem grows a cluster of numerous disc flowers during midsummer. These persist throughout the summer and into early fall. Pollination occurs through a variety of insects – flies, butterflies, moths and honeybees. Grazing on lands infested with common tansy will not reduce its prevalence because common tansy is unpalatable to livestock. Improper grazing in these areas will reduce

the density of desirable species and provide opportunities for the spread of common tansy.

Management:

There has been limited research on control of common tansy. As with all weeds, prevention of the establishment and spread of infestations is the most cost effective management tool. This can be achieved by limiting disturbance of weed-free lands. Grazing should be limited to less than 60 percent defoliation of desirable grasses. This will limit opportunities for common tansy invasion. If livestock are grazed in infested areas, they should be maintained in a holding facility for 14 days to provide time for weed seeds to pass through digestive tracts and prevent spread of weed seed in droppings. (This holding period may be unnecessary if the weed infestation consists solely of common tansy as livestock rarely graze this plant.)

In addition any stock, machinery or people that pass through infested areas should be checked for seeds, or other plant parts, before visiting uninfested lands. The most effective herbicide for common tansy control is metsulfuron (Escort®). In herbicide trials in northern Idaho, metsulfuron applied at 0.3 ounce per acre yielded 99 percent

control after three months, and 98 percent control 15 months after treatment. A higher rate of 0.5-1.0 ounce/acre of metsulfuron can give three years control. Metsulfuron should always be used with a high quality, non-ionic surfactant to ensure penetration of the herbicide into plant tissues.

This herbicide should not be used to control weedy infestations near water as metsulfuron is persistent in soil and has the potential to leach into groundwater. Accordingly, metsulfuron should not be used on any site where the depth to the water table is less than 20 feet. This limits the usefulness of this chemical for control of common tansy because the plants often grow near waterways. Glyphosate (Rodeo®) and 2,4-D amine are alternative herbicides for use near water, but they are not very effective for controlling common tansy. Best results with these herbicides have been achieved with wipe on application. In one trial, wipe on application of 2,4-D and glyphosate (Rodeo®) gave 85 percent and 75 percent control,respectively, after two years. In this same trial, spray on application yielded very poor control. Mowing or hand pulling provide alternatives to herbicide use near waterways and have been reported to marginally control common tansy. Mowing during the bud stage will prevent the growth of flowering stalks, limiting seed production and the spread of infestations by seed. If mowing is used, mower blades should be set high to limit impacts on desirable species. Hand pulling should provide similar results, but gloves and other protective clothing should be worn to prevent possible absorption of toxins through skin.

Summary:

Common tansy, an aromatic perennial with a long history of medicinal use, has become a problem weed in pastures and along roadsides, fence lines and stream banks. It is mildly poisonous but unpalatable to livestock and to humans in large doses. Cultivation for traditional folk medicines and other uses has assisted its spread throughout temperate regions of North America. Adequate control of infestations can be achieved through prevention, applications of metsulfuron (Escort®) and by mowing or mechanical removal. For more information concerning common tansy contact your local weed district or county Extension offce.

Sourced From: http://msuextension.org/publications/AgandNaturalResources/MT199911AG.pdf