Montana Field Guide

PLANTS: Rhizomatous, perennial forbs with single, erect stems that grow 40-120 cm tall. Plants have few hairs (glabrate), milky sap, and ‘fern-like’ leaves. Source: Jacobs 2008; Lesica et al. 2012.

LEAVES: Basal leaves wither early. Stem leaves are alternately arranged and petiolate but become sessile upwards. Leaf blades are about 5-15 cm long, pinnately divided into lanceolate, serrate t sharply lobed leaflets. Leaves are glabrate and gland-dotted (punctate). The main stem between leaflets (rachis) is somewhat winged. Sources: Watson in FNA 2006; Lesica et al. 2012.

INFLORESCENCE: Flat-topped corymbiform. 20-200 yellow, rayless, button-like flowers are arranged in flat-topped, compact clusters. Flower heads have an involucre of 5-10 mm across, composed of subequal-sized bracts forming 2-3 rows. Flowerheads lack ray florets (lack petals) and are composed of only yellow disc florets, 1-3 mm tall. The involucre is composed of green, overlapping bracts that have dry, thin, membranous, and translucent margins and tips. The pappus is either crown-like or absent. Sources: Watson in FNA 2006; Lesica et al. 2012.

The genus Tanacetum is authored by Carl Linnaeus and is derived from the word athanotos which implies ‘immortality’ and references its uses in medicin and preservation. This plant was also called tanazetum or athanacetum in medieval Latin, and the Old French changed it to tanesie which sounds similar to ‘tansy’.
The specific epithet of vulgare is from Latin meaning ‘ordinary’ or ‘common’. Sources: Watson in FNA 2006; Jacobs 2008.

Flowering July through September (Watson in FNA 2006).

Common Tansy and Tansy Ragwort are often confused with one another.

Common Tansy – Tanacetum vulgare, exotic and Noxious:
* Yellow flowers lack petals. Flowers have yellow disc florets and lack ray florets.
* Leaves pinnately deeply divided into equal-sized, sharp-toothed lobes.
* Plants have few hairs and leaves are gland-dotted.
* Crushed leaves have a strong menthol- or camphor-like smell from volatile oils.

Tansy Ragwort – Senecio jacobaea, exotic and Noxious:
* A biennial to short-lived perennial – pull a mature plant to find a dark-colored taproot.
* Stem leaves similar in size from base to top.
* Flowers with showy, yellow petals. Flower have both yellow ray and disc florets.
* Leaves pinnately deeply-divided into lobes that are shallowly divided.
* Lobe tips of leaves are rounded (not pointed).
* Plants have hairs, often cobwebby hairs when young leaves

Montana has 2 other Tanacetum species, both exotic:

Coastmary – Tanacetum balsamita, exotic:
* Yellow flowers lack petals. Flowers have yellow disc florets and lack ray florets.
* Leaves are simple and not lobed.

Feverfew – Tanacetum parthenium, exotic:
* Flowers have white petals (ray florets) and yellow centers (disc florets).
* Plants are minutely hairy.
* Leaves are pinnately lobed.

In Montana it grows in moist, disturbed meadows, often along streams or lakes, along roadsides and railroad tracks in the plains and valleys (Jacobs 2008; Lesica et al. 2012).

Flies, butterflies, moths, and honeybees pollinate Common Tansy flowers (LeCain and Sheley 2017).

Potential and Known Pollinators:
The following animal species have been reported as pollinators of this plant species or its genus where their geographic ranges overlap: Bombus bifarius, Bombus rufocinctus, Bombus ternarius, Bombus occidentalis, and Bombus flavidus (Thorp et al. 1983, Colla and Dumesh 2010, Koch et al. 2012).

Common Tansy is a strong competitor in low productive soils because its root system can easily acquire nutrients (Jacobs 2008). It can often be found in near-monocultures on sandy soils in riparian areas (Jacobs 2008). On high productive soils, Common Tansy is very productive, but may be more susceptible to defoliation by slugs which could shift competition in favor of rhizomatous grasses and forbs (Jacobs 2008). Readers are advised to consult Rebele (2000) for the study that led to these conclusions.

CULTURAL
Common Tansy has traditionally been considered to have insecticidal, antimicrobial, and medicinal properties (Duke 1987; Keskitoal 1999). It is reported as being used as a medicine since the times of the Ancient Greeks (LeCain and Sheley 2014). During the Middle Ages spanning the 5th to the 15th Century it is reported to be used for intestinal worms, rheumatism, fevers, digestive problems, and in large doses used to induce abortion (LeCain and Sheley 2014).

Common Tansy was used in early American history for preservation (LeCain and Sheley 2017). A governor for Massachusetts in the 1600s listed Common Tansy as a necessary plant for herb gardens (LeCain and Sheley 2014). Plants were used in burials and for packing meats and other perishables (LeCain and Sheley 2014).

The essential oils of Common Tansy have repellent properties. In the Middle Ages Common Tansy was used to repel mosquitos (LeCain and Sheley 2014). Essential oil from Common Tansy has been shown to repel the Colorado Potato Beetle (Leptinotarsa decemlineata) (Panasiuk 1984; Schearer 1984). Interplanting Common Tansy and potato plants reduced beetle populations by 60-100% (Panasiuk 1984; Schearer 1984). Another study found that particular constituents (alpha-terpineol, 4-terpineol, and alpha- plus beta-thujone, 1,8-cineole, verbenol, and verbenone) when tested separately were able to repel ticks in the laboratory (Palsson et al. 2008). The authors suggest these substances are candidates in creating an effective repellent blend, and that field studies were forthcoming (Palsson et al. 2008).

From European populations of Common Tansy, about 57 compounds have been identified and categorized into 4 main groups: 1,8-cineole, trans-thujone, camphor, and myrtenol (Jacobs 2008; Judzentiene and Mockute 2005). The amount and ratios of oil groups produced by a plant will depend upon its population, site and environmental conditions, and time of year.

* 1,8-cineolis is a monoterpene cyclic ether, used by Common Tansy as a toxin to defend itself (its leaves) against herbivory. Biological activities of 1,8-cineolis includes: allelopathy, anesthetic, antibacterial, carcinogenic, fungicide, herbicide, insectifuge, nematicide, sedative, and testosterone hydroxylase iducer.

* Thugone is a monoterpene with a menthol-like aroma. In the 19th Century it was mixed in liquor (absinthe) and consumed to increase brain activity, develop new ideas, expand imagination, cause hallucinations, and as an aphrodisiac. These effects haven been disproven, and shown that it is a GABA receptor antagonist that allows neurons to fire more easily and cause spasms. Van Gogh consumed such liquor and is reported to have experienced fits of convulsions.

* Camphor is a terpene. It is used in the manufacturing of plastics, in lacquers, varnishes, explosives, and pyrotechnics, as a moth repellent, and as a preservative in pharmaceuticals and cosmetics. It is readily absorbed by the skin and can relieve itches and pain and creates a sense of coolness. It is also used as an antibacterial injection for infected root canals.

* Myrtenol is an oxygenated monoterpene. It attracts pine bark beetles and is used to bait them. It has also been used as a beverage preservative, a flavoring, and a fragrance.

Plants reproduce from seeds and rhizomes.

RHIZOMES
Rhizomes mainly grow within the upper two feet of the soil horizon, which is relatively shallow soil. They are coarse, wiry, and have minimal development of fine hairs. These characteristics suggest that are competitive and efficient in taking up nutrients and water. Buds on the rhizomes can grow into stems or another rhizome.

FRUITS
Fruits are achenes. Each achene about 1–2 mm long, cylindric, 4-5 angled, and containing 1 seed (Lesica et al. 2012). A Montana study in Gallatin County estimated 9,966 flowers per plant (Jacobs 2008). They observed that many achenes were not developed and estimated 2,553 achenes per plant and 198,625 achenes per square meter (Jacobs 2008). About 75% of seeds collected in October germinated after one month of cold stratification implying that seeds have high viability and can germinate upon reaching maturity.

LIFE CYCLE [Adapted from Jacobs 2008]
This is based on Montana observations: In Montana stems can develop from rhizome buds in November; however, Stems typically emerge in spring after many perennial grasses have emerged. Leaves grow from mid-May to Mid-June and flower buds form in June. Plants bloom from June to August. Stems and leaves die as soil moisture depletes. Flowering and/or seed production is presumed to occur into October and November.

Seeds remain within drying flower heads unless physically dislodged. The leverage action caused by the drying of tall, stiff stems disperses seeds at or near to the parent plants. Seeds can be dispersed by wind or on water currents. Seeds in muddy soil can be transported by the foot action of humans and other animals. It is unknown if birds eat seeds or disperse them. Plants also spread by their rhizomes.

An integrated vegetative management approach provides the best long-term control, and requires that land-use objectives and a desired plant community be identified (Shelly et al. in Sheley and Petroff 1999). Once identified then an integrated weed management strategy that promotes a weed-resistant plant community and serves other land-use objectives such as livestock forage, wildlife habitat, or recreation can be developed, making control of spotted knapweed possible (Shelly et al. in Sheley and Petroff 1999).

PREVENTION [Adapted from Jacobs 2008]
Seed development must be prevented to reduce or stop spread.
* Prevent vehicles from driving through and animals from grazing within infested areas,
* Thoroughly wash the undercarriage of vehicles and wheels in a designated area before moving to an uninfested area,
* Encourage landowners to frequently monitor their land for new infestations and, when found to implement effective control methods.
* Maintain proper livestock grazing management that is more resilient to Common Tansy invasion, and
* Develop educational campaigns to teach people to not pick and transport the yellow flowers.

PHYSICAL and CULTURAL CONTROLS [Adapted from Jacobs 2008]
Hand-pulling is effective for small populations. Hand-pulling should be done when soils are moist in order to remove all rhizomes. Rhizomes can re-sprout. Follow-up treatments will be necessary until all rhizomes and the seed bank are deleted.

Mowing reduces flower and seed production if done before the bloom stage. To maintain the vigor of desirable plants it is recommended to keep a 4-inch or greater stubble height. Plants in seed should not be mowed because it will spread them. Mowers must be carefully and thoroughly cleaned to prevent spreading seeds.

Tilling can control Common Tansy where it occurs in fields. However, disturbing the soil can cause germination and/or fragmented rhizomes to grow. Follow-up treatments will be necessary until all rhizomes and the seed bank are deleted. Farming equipment must be carefully and thoroughly cleaned to prevent spreading seeds.

Prescribed burning should be integrated with other control methods, such as herbicide, grazing, and revegetation management. Burned plants can regenerate from rhizomes. Burning can remove dense dried-up litter. Burning can be used on actively growing plants to remove dead material in preparation for an herbicide application.

Revegetation should be integrated with other control methods, such as herbicide or hand-pulling. Plant competition reduces the invasiveness of Common Tansy and increases the effectiveness of control applications. Suppressing the population through hand-pulling or an herbicide application will help in re-vegetation efforts. Species selected for re-vegetating should be appropriate for management objectives, adapted to the site conditions, and be competitive. Planting with appropriate native plants is highly encouraged. Refer to Montana Plant Materials Technical Note 46, Seeding Rates for Conservation Species for Montana, and Extension Bulletin EB0019, Dryland Pasture Species for Montana and Wyoming for possible species selection and seeding rates. Common tansy is often found in all the hydrologic zones of stream banks and riparian areas. Conservation practices that address riparian restoration, such as Channel Bank Vegetation (Code 322), may be needed after common tansy control to maintain hydrological cycles and prevent soil and water resource concerns such as erosion and sedimentation.

GRAZING CONTROLS [Adapted from Jacobs 2008]
Common Tansy is reported to be toxic to livestock. Cattle in the mid-west have reported to abort their fetus. Some ingestion might be okay and wild ungulates might be more tolerant to the plant. It has been suggested that herbivores have a toxin blood-level feedback mechanism, whereby, that when a certain threshold is reached animals will no longer graze Common Tansy.

Sheep have been used to manage Common Tansy in Montana. However, it is recommended that that female sheep be removed from areas with Common Tansy four weeks prior to breeding to avoid any potential reproductive problems. In a Montana study, sheep reduced the above-ground biomass of Common Tansy by 90% while consuming similar levels of perennial grasses. Long-term effects from grazing are unknown, but it is hypothesized that Common Tansy populations would decline allowing perennial grasses to increase.

CHEMICAL CONTROLS [Adapted from Jacobs 2008]
An integrated vegetative management approach provides the best long-term control, and requires that land-use objectives and a desired plant community be identified (Shelly et al. in Sheley and Petroff 1999). Once identified then an integrated weed management strategy that promotes a weed-resistant plant community and serves other land-use objectives such as livestock forage, wildlife habitat, or recreation can be developed, making control of spotted knapweed possible (Shelly et al. in Sheley and Petroff 1999). For up to date information on herbicides, consult Greenbook.

Common Tansy had been controlled using Metsulfuron, chlorsulfuron, or by mixing them. These chemicals are not selective and can kill shrubs, grasses, and other broad-leaf plants. Applications can be applied to plants growing to the water’s edge, but must not be applied directly to surface water of any depth. A non-ionic surfactant at 0.5% volume/volume or methylated seed oil at 2% volume/volume in a spray solution is recommended. Visible effects of the herbicides may not be apparent until 45 days after the treatment.
* metsulfuron applied at a broadcast rate of 0.5 ounces per acre at the late bud stage (late June) provided almost 100% control for one year for a population growing on moist soil.
* metsulfuron and chlorosulfuron mixed together at the individual rate of 0.25 ounce per acre had similar results as above.

At sites without a high water table, Picloram applied to actively growing plants in the bud to bloom stages can be used to control Common Tansy. Picloram mixed with dicamba and applied to the budg stage provided 98% control for 24 months after treatment.

Where Common Tansy is growing in water, imazapyr applied at 1 quart per acre may provide some control.

Useful Links:
Montana Invasive Species website
Montana Biological Weed Control Coordination Project
Montana Department of Agriculture - Noxious Weeds
Montana Weed Control Association
Montana Weed Control Association Contacts Webpage.
Montana Fish, Wildlife, and Parks - Noxious Weeds
Montana State University Integrated Pest Management Extension
Weed Publications at Montana State University Extension - MontGuides

Common Tansy reduces available forage because cattle and horses generally avoid them (Jacobs 2008). The volatile oils in the leaves deter grazing by livestock, and native ungulates are rarely observed eating them.

Common Tansy can form dense patches which out-compete native plants and reduces bio-diversity (Jacobs 2008).

It may reduce habitat for pollinating insects (Jacobs 2008).