Controlling Common Tansy with Sheep

Final Report for FW05-007

Project Type: Farmer/Rancher
Funds awarded in 2005: $3,422.00
Projected End Date: 12/31/2006
Region: Western
State: Idaho
Principal Investigator:
Expand All

Project Information


The project was conducted in two locations, Andrews and McFarland ranches. The common tansy sites were enclosed with electric net fencing, and the sheep grazed each site until 90-100% of the common tansy had been consumed. Each spring, the project coordinator and technical advisor collected percent cover, stem height and number of stems present at designated plots. Stem height readings were also collected about every 10 days after the sheep left each site.

The project’s primary goal was to control common tansy with sheep grazing several times a year and by timing the grazing so that the plants could not reproduce by seed.

Several accomplishments were made that are not represented in the collected quantitative data. The edge of each project site was reduced slightly each year, and it took fewer and fewer days each time a site was grazed.

The project mostly had positive impacts on the affected sites. The spread of common tansy to adjacent pastures was reduced, and irrigation time has been reduced as the grazing diminished decadent stems and increased access to the ditch bank. Grazing also increased the palatability of common tansy to other livestock species. One drawback is that the sheep graze everything within the electric fence enclosure, so desirable plants are affected along with common tansy.

• Interrupt common tansy’s reproductive cycle, the first step in controlling weedy species
• Reduce root reserves in the plants as measured by stem counts and plant height
• Learn more about common tansy and its chemical compounds
• Show that grazing is an effective control option with this particular plant species.

Before the project was begun, plots a foot square with the center marked by a fiberglass fence post were set up at each project site. At the beginning of each grazing season, each plot was photographed and the percent cover estimated, the stem height measured and the stems counted. After sheep had grazed the site, about every 10 days, the regrowth was measured next to the fiberglass post. Once cows had access to the site in the fall, the height measurements were discontinued.

The timing of grazing was the significant factor in reducing reproduction and root reserves. The first grazing was timed for the spring so that the plants had some height and had used up some of their root reserves. The second grazing was timed so that most of the plant stems were forming immature flower heads, which not only impacts the plant’s ability to store reserves for the winter but also reduces the plant’s ability to spread to new areas.

The 2006 plot data show that the grazing is starting to have an effect on the common tansy root reserves and biomass. The second grazing of McFarland’s site is approximately 80 days after the first grazing. In 2006, it took nearly a month longer than in 2005 for the plants to recuperate after the spring grazing. The Andrews site was grazing in 2006 in about the amount of same time as in 2005, but with only half the number of sheep.

Knowledge about common tansy and its chemical content was gained by searching the Internet and from conversations with staff at the USDA-ARS Poisonous Plant Research Laboratory. Common tansy does contain chemicals that can be neuro-toxic and cardio-toxic, but the actual compound(s) or compound combinations have yet to be determined. This is research that could be conducted by the Poisonous Plant Research Laboratory, but it was beyond the scope of this Western SARE study.

To assess whether the chemicals in the common tansy were affecting ewes, blood samples were collected in July 2005 with the help of a veterinarian before grazing, after grazing and 10 days after grazing. Dr. James England of the University of Idaho Caine Veterinary Teaching Center found no significant changes in the ewes’ blood chemistry.

The data from this project show that common tansy is palatable to sheep and that sheep can affect plant populations. Once the common tansy was grazed by the sheep and kept in a vegetative state, cattle started to utilize the plant as well.

Reducing common tansy enhances agricultural resources by increasing desirable livestock forage, plant diversity/habitat, irrigation water and ditch bank stabilization. Economic benefits include reducing contaminated crop products, increasing desirable forage in pastures, increasing water flow to the desired forage species and, possibly, sheep producers deriving another source of income through prescription grazing.

For producers who might consider adopting this practice on their own operations, here are a few suggestions:

• Consider the site in regards to possible wildlife activity. Deer, elk and moose can wreck a good project and the electric net fencing it uses. In areas of high wildlife traffic, consider moving the sheep to a night pen and opening the electric fence along game trails.
• Consider the sheep species and their habits. Some breeds flock and herd better than others. It is best to train sheep to the electric netting inside a secure corral system before the project begins.
• Use plenty of supplements and have fresh water for the sheep. Ewes will stop consuming common tansy if their dietary needs are not being met. Common tansy has only 4% crude protein compared with around 8% for grass. Water is essential to flush the fibrous material through the sheep’s digestive systems.

Producers who had had previous experience with common tansy said they were amazed that common tansy could be used as a forage, and they were impressed with the reduction in biomass with just a few grazings. However, each of the producers interviewed already had a chemical control plan in place and intended to continue in that direction. The water master for ditches in the area of the project said he was impressed that just a single grazing could have such an impact, and he said it was easier to drive to the diversion to take readings.

Another project could look at grazing common tansy for at least four to five years. Research conducted by BEHAVE indicates that it takes at least four years of repeated grazing before there is any significant difference in stem counts and weed density.

A project could also look at desirable plants with a common tansy project site. A 100-foot transect with a reading taken every 10 feet could reflect how the desirable plants are responding.

It would also be interesting for a researcher to define or prove the chemical compounds in common tansy, which would produce valuable information on toxicity for livestock producers.

The project coordinator has made several presentations to local audiences using a PowerPoint presentation. In addition, an article on the project was distributed to several newspapers, extension services in Idaho and Montana, the American Sheep Industry’s Sheep Industry News and several agricultural magazines.

A website on the project is also being developed. The address is:


Click linked name(s) to expand/collapse or show everyone's info
  • Shannon Williams


Participation Summary

Research Outcomes

No research outcomes
Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.