Common name:

Garlic mustard, Jack-by-the-hedge

Scientific Name:

Alliaria petiolata (syns. Alliaria alliaria)

Noxious Weed Listing:

• WeedWise: Containment
• State of Oregon: Class B
• State of Washington: Class A
• 4-County CWMA: Class A
• Columbia Gorge CWMA: Class A

Description:

General:

Garlic mustard is a biennial plant in the Brassicacaea (Mustard) family. Garlic mustard is an aggressive woodland invader throughout much of the continental United States. It affects both disturbed and pristine woodlands and has become one of the worst invaders of forests in the American Northeast and Midwest regions. The plant can form dense stands up to 4 ft in height and can aggressively out-compete other native plants. The most identifying set of factors for this plant are its white, cross-shaped (cruciform) flowers and presence of a garlic odor on crushed leaves.

Leaves:

The leaves of this plant are stalked with kidney-shaped to triangular leaves and a coarsely-toothed margin. The leaves vary in length from less than 1 inch to more than 6 inches. The basal rosette features primarily kidney-shaped leaves while the mature flowering stalks have triangular leaves. When crushed, the leaves typically have a pungent garlic-like odor.

Flowers

Garlic mustard flowers have four small, white petals that grow in the shape of a cross. The flowers emerge on mature plants from May to June in our region. The flowers have 4 sepals that are generally half as long as the petals.

Fruits

Garlic mustard produces elongated seed pods that are slender, slightly curving, and up to 3 inches long. Adult plants can produce up to 8000 seeds which can remain viable in the soil for more than 10 years. The seeds are brown to black, grooved, and oblong when mature.

Roots

This plant has roots that typically feature an S-shaped hook or bend just below the soil line on its single taproot.

Reproduction:

This species reproduces exclusively by seed. Seeds most often fall near the parent plant, but, importantly, are also transported by moving water, wildlife, and contaminated equipment such as hiking boots, mowers, and vehicles. Stands of garlic mustard can produce more than 62,000 seeds per square meter. The seeds germinate in the late winter and spring at typically very high densities and form rosettes in their first year of growth. The rosettes overwinter and begin to bolt and flower the following spring and summer. The seeds can survive in the soil for up to 10 years and still germinate.

Habitat:

Garlic mustard grows best in filtered to partial light. However, in our region garlic mustard can grow in an exceptionally wide variety of habitats including both open and shaded ones as well as upland and stream-side locations. It grows on sand, loam, and clay soils. Where this plant is most abundant in Clackamas County, it is predominantly found near rivers, roadsides, and on non-turf portions of parks and residential properties.

Impacts:

• Garlic mustard can invade healthy forests and severely reduce biodiversity through highly successful competition for light.
• It is thought to produce a toxin that kills soil fungi that other native plants are dependent on, including native tree seedlings.
• Degrades wildlife habit and reduces the diversity of animals in infested areas.

Introduction:

Garlic mustard is native to Europe, North Africa, and parts of Asia. It was originally introduced to North America as a garden and medicinal herb. The first documentation of garlic mustard growing in North America is from 1868 on Long Island, NY. In Oregon, the earliest herbarium record is from 1959 on the Reed College campus. While it has been around for numerous decades, it has only been in the last two decades that the plant has begun to rapidly expand its geographic range in our area. This lag period is a common phenomenon that many invasive plants exhibit when introduced to a new region. Significant efforts throughout the Portland region are underway to contain, suppress, and, in many areas, attempt to eradicate garlic mustard populations.

Distribution:

Clackamas County:

This plant can be found in several communities and river systems in Clackamas County, but it is not widespread. This species is actively surveyed for, but the mapped distributions do not represent the full extent of the population in Clackamas County. Please report any sightings of this weed, even if nearby populations have already been mapped.

State of Oregon:

• Oregon iMapInvasives
• Oregon Weedmapper
• Oregon Flora Plant Atlas

United States:

• EDDMapS
• USDA Plants Database

Management:

Strategy:

The management of invasive weeds is best served through a process known as Integrated Pest Management (IPM).  IPM is a weed management methodology that utilizes:

• Management thresholds to determine when and if to initiate control,
• The ecology and life history characteristics of the targeted invasive weed,
• Site-specific conditions and land use considerations to inform management practices,
• The effectiveness and efficiency of various control methods.

An IPM based strategy ensures the maximum effectiveness of treatment measures.  IPM strategies typically use more than one management method to target one or more susceptible life stages.  It is adaptive to site conditions in the field and to the response of a plant to management.  The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan.   The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a weed particular infestation.

Manual:

Garlic mustard can be effectively controlled through hand pulling. Care must be taken to remove the taproot completely. Root fragments left in the ground can resprout. The highest priority for all methods of control is to target the second-year plants to prevent seed production. Hand pulling is often, however, not practical on well-established, extensive populations or in areas with compacted soils. Removed plant material should be bagged and placed in the trash.

Mechanical:

Generally, mowing is not recommended. However, when done properly frequent mowing can reduce or eliminate seed production. Plants should be cut as low as practical and should be cut repeatedly throughout the spring and early summer. Be sure to monitor your work to ensure that you are effectively suppressing flowering and seed production. Be sure to prevent the spread of seeds by cleaning equipment well and managing any adjacent, unmowed affected areas.

Cultural:

Garlic mustard is not toxic and is edible.  Grazing animals tend to avoid garlic mustard due to its pungent garlic-like odor but will graze it when more desirable vegetation is depleted.   Garlic mustard is best grazed before flowering to reduce seed production, but grazing alone will not eliminate garlic mustard.  For dairy producers, grazing is not recommended as garlic mustard is known to impart an unpleasant odor to the taste of milk.

Chemical:

Before you Start:

• Before purchasing any herbicide product it is important to read the label.  The label is the Law.  Carefully review all parts of the label even if you have used the product before.  Select a product that is most appropriate for your site.  If you have questions, ask your vendor before purchasing a product.
• When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times.  If any information provided here contradicts the label, the label takes precedence.  Always follow the label!
• Protect yourself.  Always wear the recommended protective clothing identified on your label and shower after use.
• When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
• Do not apply during windy or breezy conditions that may result in drift to non-target plants
• Avoid spraying near water.  Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
• Avoid exposure to pets, pollinators, and wildlife.  Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried.  Avoid spraying when insects and animals are active.  Avoid spraying blooming plants to minimize any effects to bees and pollinators.
• Be sure to store any chemicals, out of the reach of children and pets to keep your family safe.

Herbicides:

The mention of any brand name product is not, and should not be construed as an endorsement for that product.  They are included here only for educational purposes.  Suggested rates are generalized by active ingredient.  Specific rates will vary between products.  Be sure to review the label before application and use the recommended label rate at all times.

Biological:

There are no approved biological control agents ready for release in the United States.  Currently four weevils under consideration as potential biological control agents.  These include two stem mining insects (Ceutorhynchus alliariae &  Ceutorhynchus robertii), one root feeder (Ceutorhynchus scrobicollis), and one weevil (Ceutorhynchus constrictus) that develops in the garlic mustard seeds.

Disposal:

Please dispose of mature seeding producing garlic mustard plants as trash. Plants still in the rosette state can be disposed of as yard waste for commercial composting.  It is generally not recommended to compost garlic mustard on site, even for immature plants.  Soil residues from pulled plants are commonly contaminated by garlic mustard seed, and home compost systems inconsistently reach temperatures sufficient to destroy seeds.

Follow-Up:

Any control plan for garlic mustard will typically require at least five years of control and/or monitoring. Well-established populations will often not show significant reductions in population size until several years of treatments have been performed. Monitor presumed eradicated patches for at least a few years to ensure that no additional seedlings emerge.

Best Management Practices:

Small Infestations:

• Consider the land use practices on site.  Identify any site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify garlic mustard.  If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• If you are working on public property be sure to coordinate with the land manager.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Hand pull all adult plants after bolting has been initiated in the spring, typically sometime in April. Bag plants and place in the trash.
• Do not hand pull once seed production has begun to reduce the risk of spreading seeds.
• Repeated visits and a very thorough survey of infested areas over the course of the spring is required to get good control using manual methods.
• Applications of glyphosate or triclopyr at recommended label rates can be very effective on smaller sites, particularly when dealing with dry and compacted soils.

Large Infestations:

• Consider the land use practices on site.  Identify any site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify garlic mustard.  If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Apply glyphosate or triclopyr at recommended label rates to bolting plants or flowering plants and any rosettes or seedlings present. Glyphosate may not effectively halt seed production when applied to late flowering individuals.
• It is common that seedlings and even mature plants are missed, even with very thoroughly control efforts. Plan to revisit your application site approximately 2-3 weeks after application to perform follow-up control. If the patch is still flowering, reapply using triclopyr. If seed production has begun, but viable seeds are not present, switch to hand pulling to remove remaining plants. If viable seeds are present, leave the site until next year and do not hand pull to avoid spreading seed.

Fun Facts:

• More than 8,000 results are returned from a scholar.google.com search for Alliaria petiolata.
• Garlic mustard affects 38 U.S. states
• Garlic mustard is one of the most nutritious leafy greens ever analyzed. It has more fiber, beta-carotene, vitamin C, vitamin E, and zinc than spinach, broccoli leaves, collards, turnip greens, and kale.

Gallery:

Detail of flowers

infestation

Seed pods

Garlic mustard stem and flowers

Garlic mustard flowers

Garlic mustard rosette

Garlic mustard flowers

Garlic mustard seedling

Garlic mustard control

Additional Information:

• Oregon Department of Agriculture: Garlic mustard profile
• Oregon State University Extension: Forestry garlic mustard management
• City of Portland: Garlic Mustard
• Bugwood Wiki: Alliaria petiolata
• USDA Plants: Alliaria petiolata
• King County Washington: BMP garlic mustard
• Center for Invasive Species and Ecosystem Health
• The Nature Conservancy Element Stewardship Abstract

References:

1. Bugwood Wiki.  Alliaria petiolata.  https://wiki.bugwood.org/Alliaria_petiolata.  (accessed January 7th, 2015)
2. Christy, J. A., A. Kimpo, V. Marttala, P. K. Gaddis, & N. L. Christy.  2009.  Urbanizing Flora of Portland Oregon 1806-2008.  Native Plant Society of Oregon Occasional Paper 3 pg. 218.
3. DiTomaso, J.M., G.B. Kyser, S.R. Oneto, R. G. Wilson, S. B. Orloff, L. W. Anderson, S. D. Wright, J.A. Roncoroni, T.L. Miller, T.S. Prather.  2013.  Weed Control in Natural Areas in the Western United States.  Davis, CA: UC Weed Research and Information Center.  pp 341-343.
4. Kallas, John. “Garlic Mustard.” Edible Wild Plants. Layton: Gibbs Smith, 2010. 231-48.
5. Kaufman, S.R. and W. Kaufman.  2007.  Invasive Plants: Guide to Identification and Impacts and Control of Commons North American Species. Stackpole Books.  Mechanicsburg, PA.  pp.277-280.
6. King County Noxious Weed Control Program.  2010.  King County Best Management Practices for Controlling Garlic Mustard.  https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/BMPs/Garlic-Mustard-Control.pdf  (accessed January 7th, 2015).
7. The Nature Conservancy. Element Stewardship Abstract for Alliaria petiolata (Allaria officianalis) Garlic Mustard.  https://www.invasive.org/weedcd/pdfs/tncweeds/allipet.pdf.  (accessed January 7th, 2015)
8. Oregon Flora Project. 2013.  Oregon Plant Atlas: Alliaria petiolata.  https://www.oregonflora.org/atlas.php.  (accessed January 7th, 2015)
9. Peachey, E., editor. 2015. Pacific Northwest Weed Management Handbook [online]. Corvallis, OR: Oregon State University. https://pnwhandbooks.org/weed (accessed Feb 26, 2016

Common name:

Blessed milkthistle, Milk thistle, Marian thistle, Mary thistle, Saint Mary’s thistle, Mediterranean milk thistle, Variegated thistle

Scientific Name:

Silybum marianum. (Syn. Carduus marianus)

Noxious Weed Listing:

• WeedWise: Priority
• State of Oregon: Class B
• Four County CWMA: Class A

Description:

General:

Blessed milkthistle is a sparsely branched thistle growing up to 6 feet tall and forming dense stands. It’s a tap-rooted biennial or annual that forms large rosettes followed by 2 inch purple blooms borne singly on unbranched, grooved and somewhat cottony stems.

Leaves:

Leaves are oblong to lanceolate, hairless, shiny dark green with distinctive white patterns running along the veins, reaching up to 20 inches long and 10 inches wide. The white mottling gives the plant the appearance of having been drenched in milk, thus the common name. Leaf margins are tipped with spines up to 1/2 inch in length. Large rosettes can reach 3 feet in diameter.

Flowers

Solitary composite red-purple flowers reach 2 inches in diameter and are surrounded by leathery, spiny, hairless bracts. The all-disk flowers are similar to other thistles, with large spines extending out in layers from under the pincushion-flower head. Plants flower from April to October.

Fruits

Dark brown, relatively heavy hairless achenes, about 1/2 by 1/4 inch, form in autumn.

Roots

Plants grow from long white taproots.

Reproduction:

Reproduction is from seeds. Plants are typically biennial in our area, so they die after going to seed. Seeds are relatively heavy and dispersal is usually by animals, equipment, vehicles or contaminated hay. Plants can produce more than 6,000 seeds per year which can remain viable in the soil for at least 9 years, where disturbance will cause them to germinate. Seeds often germinate following the first rains of the season but may continue to germinate through the winter.

Habitat:

Blessed milkthistle can be found in full sun or part shade.  They typically grow in heavily grazed pastures and on roadsides where nitrogen is high and disturbance regimes are frequent. This plant is also traded horticulturally and found in ornamental and medicinal gardens.

Impacts:

• A serious threat to livestock. Ingestion by livestock can cause nitrate poisoning and death.
• Forms dense stands that shade out forage species and exclude livestock.
• Spines can cause injury to people and livestock.
• Displaces native vegetation.

Introduction:

Native to southern Europe, blessed milkthistle was probably introduced to the US as a medicinal plant by early colonists. It has become common in Canada and throughout the southern United States.

Distribution:

Clackamas County :

Blessed milkthistle is relatively rare in Clackamas County, with populations associated with disturbed and unmanaged sites.  Milkthistle is occasionally cultivated as an herbal supplement.

State of Oregon:

• Oregon iMapInvasives
• Oregon Weedmapper
• Oregon Flora Plant Atlas

United States:

• EDDMapS
• USDA Plants Database

Management:

Strategy:

The management of invasive weeds is best served through a process know as Integrated Pest Management (IPM). IPM is a weed management methodology that utilizes:

• Management thresholds to determine when and if to initiate control,
• The ecology and life history characteristics of the targeted invasive weed,
• Site-specific conditions and land use considerations to inform management practices,
• The effectiveness and efficiency of various control methods.

An IPM based strategy ensures the maximum effectiveness of treatment measures.  IPM strategies typically use more than one management method to target one or more susceptible life stages.  It is adaptive to site conditions in the field and to the response of a plant to management.  The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan.   The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP’s), which outlines the best approach for controlling a weed particular infestation.

Manual:

Blessed milkthistle responds well to manual control for small outbreaks. Dig plants whenever you find them, prior to flowering.  Once they are flowering, be sure to carefully bag and dispose of plants to prevent seed set. Viable seeds will continue to form after plants are dug up and it can be difficult to contain mature seed heads without spreading seeds.   In this case, carefully remove and bag all flower and seed heads before digging plants. Where mature plants are removed search carefully for small rosettes or germinating seeds.  Return to the same location in spring and fall, and continue to monitor for several years. For best control, sow native plant seeds on disturbed soils to suppress milkthistle germination.

Mechanical:

Cultivation and tillage can be effective control options for seedlings, but soil disturbance will increase germination in the soil seed bank. Mowing will not eradicate milkthistle.  Plants are able to re-sprout and flower in the same season after being mowed. Plants can persist as perennials in a regular mowing cycle and may flower below the level of the mower, spreading seeds to new areas. Mowing may also increase the amount of toxic material ingested by grazing animals, as milk thistle becomes more palatable as it wilts. If you do mow near a milkthistle infestation, be sure to clean your mower to prevent spreading seeds to new locations.

Cultural:

Good grazing practices and management for grasses and forage species will reduce the disturbance regime and decrease the opportunity for milk thistle to become established. Minimize soil disturbance and re-vegetate to prevent infestations. Burning is not an effective control and can encourage seed germination and establishment.

Chemical:

Herbicides should only be used at the rates and site conditions specified on their label.

For control of large milk thistle infestations, apply a selective broadleaf herbicide and surfactant in the spring and again in the fall.  Infested areas should not be mowed  until the herbicide has had a chance to work. Continue to monitor areas in spring and autumn for several years following treatment.

Before you Start:

• Before purchasing any herbicide product it is important to read the label.  The label is the Law.  Carefully review all parts of the label even if you have used the product before.  Select a product that is most appropriate for your site.  If you have questions, ask your vendor before purchasing a product.
• When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times.  If any information provided here contradicts the label, the label takes precedence.  Always follow the label!
• Protect yourself.  Always wear the recommended protective clothing identified on your label and shower after use.
• When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
• Do not apply during windy or breezy conditions that may result in drift to non-target plants
• Avoid spraying near water.  Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
• Avoid exposure to pets, pollinators, and wildlife.  Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried.  Avoid spraying when insects and animals are active.  Avoid spraying blooming plants to minimize any effects to bees and pollinators.
• Be sure to store any chemicals, out of the reach of children and pets to keep your family safe.
• Product labels and formulations change regularly.  Check the Pacific Northwest Weed Management Handbook and the label for current control recommendations.

Herbicides:

The mention of any brand name product is not, and should not be construed as an endorsement for that product.  They are included here only for educational purposes.  Suggested rates are generalized by active ingredient.  Specific rates will vary between products.  Be sure to review the label before application and use the recommended label rate at all times.

Biological:

Blessed milkthistle is impacted by Rhinocyllus conicus, a seed head weevil first released in 1979.  Rhinocyllus conicus is widespread in Oregon and feed heavily on blessed milkthistle.  The presence of Rhinocyllus conicus offered excellent control of blessed milkthistle but is not recommended.  Rhinocyllus conicus targets many native thistles species, and its redistribution is discouraged.  Interstate distribution of this biological control is prohibited.

Disposal:

Bag all flowers and seed heads and dispose of in the garbage.  Seeds will continue to mature after a plant is pulled.  Do not compost seeds or flower heads.

Follow-Up:

Sites should be monitored for several years after the removal of mature plants. Viable seeds can last at least 9 years in the soil.

Best Management Practices:

Small Infestations:

• Consider the land use practices on site.  Identify site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify blessed milkthistle.  If you are unsure about your weed, bring a sample to the Conservation District and we can help to identify your particular plant.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Small infestations can be controlled manually by digging entire plants.  Dispose of plants by bagging the entire plant and placing in the garbage. Do not compost or feed to livestock.
• Replace any divots created when removing the plants to lessen the amount of disturbed soil.
• If using herbicide, apply using a spot spray technique to minimize non-target injury.
• Monitor site throughout growing season and remove any new plants.
• If using an herbicide in a grassy area, use a selective herbicide with a non‐ionic surfactant to avoid injury to the grass.
• If using herbicides where livestock may be present, be aware of grazing restrictions and damage to forage plants.

Large Infestations:

• Consider the land use practices on site.  Identify site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify blessed milk thistle.  If you are unsure about your weed, bring a sample to the Conservation District and we can help to identify your particular plant.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Apply selective herbicides with a non‐ionic surfactant in the spring before any flowers appear.
• Remove all grazing animals from infested areas.
• Apply herbicide utilizing a spot spray or broadcast application.
• Apply herbicide on warm days when winds are low.
• Try not to disturb the soil. Replace any divots created. Maintain a healthy vegetative cover.
• Continue to monitor site throughout growing season and for a few years post-treatment. Remove any new growth.
• Check the label for specific information on wind and rain guidelines.

Fun Facts:

• Silymarin is a chemical extracted from the blessed milkthistle seeds, is thought to help repair liver cells damaged by alcohol and other toxic substances, including the toxins found in Amanita phalloides, the death cap mushroom.
• Blessed milkthistle has been used medicinally for over 2000 years.
• Blessed milkthistle is a nitrogen accumulator, and can cause nitrate poisoning in livestock.

Gallery:

Blessed milkthistle infestation

Blessed milkthistle seedlings

Blessed milkthistle seedheads

Blessed milkthistle (Silybum marianum) rosette

Mature blessed milkthistle

Blessed milkthistle

Blessed milkthistle (Silybum marianum) flower head

Blessed milkthistle leaf

Blessed milkthistle seedling

Blessed milkthistle rosettes

Blessed milkthistle fruits

Milkthistle seedlings emerging after the onset of fall rains.

Additional Information:

• Washington State Noxious Weed Control Board: Silybum marianum
• Oregon State University Extension: Invasive Weed ID and Management
• Weed Control in Natural Areas in the Western United States
• Pacific Northwest Weed Management Handbook: Thistle Control
• King County Washington: Blessed milkthistle Best Management Practices
• Center for Invasive Species and Ecosystem Health

References:

1. DiTomaso, J.M., G.B. Kyser, S.R. Oneto, R. G. Wilson, S. B. Orloff, L. W. Anderson, S. D. Wright, J.A. Roncoroni, T.L. Miller, T.S. Prather.  2013.  Weed Control in Natural Areas in the Western United States.  Davis, CA: UC Weed Research and Information Center.  pp 371-2.
2. King County Noxious Weed Control Program.  2011.  King County Noxious Weed Control Program, Best Management Practices: Milk Thistle.  https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/BMPs/Milk-Thistle-Control.pdf  (Retrieved Jan. 6, 2015).
3. Oregon Flora Project. 2013.  Oregon Plant Atlas: Rubus bifrons.  https://www.oregonflora.org/atlas.php.  (Retrieved Jan. 6, 2015)

Common name:

Tansy Ragwort, Stinking Willie, Staggerwort, Tansy butterweed

Scientific Name:

Senecio jacobaea (syn. Jacobaea vulgaris)

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• Four County CWMA: Class C

Description:

General:

Tansy ragwort is a tall biennial plant in the sunflower family.  It can grow up to 6 feet in height at maturity.  The rigid stems of tansy ragwort are green with an occasional reddish tinge.  Plants typically arise from a single stem that becomes branched at the top of the plant, forming flat clusters of bright yellow flowers. The yellow daisy-like flowers have dark yellow to orange centers.  Leaves are dark green and ruffled in appearance.  Tansy ragwort grows as a rosette in its first year before transitioning into the mature flowering form in its second year of growth.  Tansy ragwort can form dense patches, particularly on disturbed sites.  This noxious weed is dangerous to humans and livestock due to a poisonous alkaloid (hepatotoxic pyrrolizidine) in its tissue which causes liver damage when ingested.

Leaves:

Tansy ragwort leaves are evenly spaced and alternate along the stem.  Leaves decrease in size toward the top of the plant. Leaves can be smooth, or lightly hairy on their underside of lower leaves. Leaves are dark green and generally lighter on the underside. The leaves of Tansy ragwort are pinnate and appear to be ruffled in appearance.

Flowers

Tansy ragwort has bright yellow, showy flowers forming a flat-topped cluster at the end of the stem. There can be anywhere from 20 to 60 flowers in a cluster. The daisy-like flowers have numerous disc flowers surrounded by 10-15 evenly spaced ray flowers. Peak flowering occurs from July to September.

Fruits

Tansy ragwort produces very small, cylindrical seed like fruits called achenes.  The achenes from the ray flowers are smooth while the achenes from the disc flowers are hairy.  The achenes have a dandelion-like set of bristly hairs called a pappus which aids in dispersal of the seed by the wind.  Adult plants can produce up to 200,000 seeds.  Seeds can remain viable in the soil for more than 10 years.

Roots

The root system of tansy ragwort consists of a distinct taproot or crown with  lateral  and secondary roots spreading away from the plant. Roots can reach 1 foot deep into the soil.  New root shoots are easily formed if a plant is mowed, cut, or injured.

Reproduction:

Tansy ragwort reproduces predominantly by seed, but in some instances can also spread vegetatively.   Seeds are dispersed by wind or by wildlife. Seeds can also be transported by machinery, contaminated soil and hay, and boots and clothing.and by seed. Vegetative reproduction occurs when roots or the crown are injured and new shoots develop. The fragments from the injured roots can generate new shoots.

Habitat:

Tansy ragwort is opportunistic plant often found in disturbed areas. Tansy ragwort likes a cool and wet climate, well-drained soils and full to partial sun. Patches are found in pastures, fields, grasslands, vacant land,  waste places, horse trails, roadsides, rangeland, riparian areas, forested areas, and clear cuts.  Areas of greatest concern are improperly managed pastures and disturbed areas.

Impacts:

• Competes with and displaces native vegetation.
• Contains alkaloids that are lethal to most livestock, with death occurring after consuming 3-8% of body weight (Boersma et al. 2006).
• Can contaminate hay, milk, and honey.
• Reduces pasture productivity.

Introduction:

Native to Eurasia, tansy ragwort was first reported in the United States in California in 1912. In Oregon, tansy ragwort was believed to have been introduced through contaminated ballast in the early 1900s (Christy et al., 2009).  The first documented herbaria record for tansy ragwort is from Multnomah county in 1922. Since becoming established it has spread across western Oregon.

Distribution:

Clackamas County:

Tansy ragwort can be found throughout Clackamas County.  It is very widespread and directly impacts properties throughout the county.  As a ubiquitous weed,  this is not a species that is actively surveyed.  Mapped distributions do not represent the full extent of the tansy ragwort population in Clackamas County.

State of Oregon:

• Oregon iMapInvasives
• Oregon Weedmapper
• Oregon Flora Plant Atlas

United States:

• EDDMapS
• USDA Plants Database

Management:

Strategy:

The management of invasive weeds is best served through a process known as Integrated Pest Management (IPM).  IPM is a weed management methodology that utilizes:

• Management thresholds to determine when and if to initiate control,
• The ecology and life history characteristics of the targeted invasive weed,
• Site-specific conditions and land use considerations to inform management practices,
• The effectiveness and efficiency of various control methods.

An IPM based strategy ensures the maximum effectiveness of treatment measures.  IPM strategies typically use more than one management method to target one or more susceptible life stages.  It is adaptive to site conditions in the field and to the response of a plant to management.  The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan.   The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a  particular weed infestation.

Manual:

Tansy ragwort can be effectively controlled by biological, chemical, and manual methods. It is an important plant to control, especially in hay and pasture lands, where it can harm grazing animals. As with any control method, it is important to avoid disturbing the soil as much as possible.  Soil disturbance can bring buried seeds to the surface, and lead to increased soil erosion.   Due to the toxicity of tansy ragwort, be sure to wear gloves and protective clothing when removing this plant.

Tansy ragwort can be controlled by digging or pulling. Plants should ideally be pulled between May and June, after they bolt and before they flower. Pulling and digging is easier when the soil is moist.  Later in the season, soils dry and harden making tansy ragwort plants much more difficult to remove.   Rosettes should be dug up, removing as much as the root as possible. Grubbing tools, hoes, and shovels can be used.

Mechanical:

Mowing is not a suggested means of control for tansy ragwort.  While mowing may prevent the plant from immediately producing seeds, it also stimulates additional vegetative growth.  This leads to more plants and more stems per plant in the same season. Mowing is especially problematic in pastures, where it can spread the toxic leaves making it harder for grazing animals to avoid.

Cultural:

Grazing of Tansy ragwort is generally discouraged.  For most grazing animals, the plant is highly toxic.  Sheep are known to tolerate the alkaloids, but tansy ragwort is not considered desirable forage.  The impacts of grazing on tansy ragwort is similar to mowing, and may help to suppress the plant, but is not an effective control method.

Chemical:

Herbicide application is an effective means to control tansy ragwort infestations. Tansy ragwort is susceptible to several systemic herbicides. Be cautious when using herbicides on pasture land with grazing animals.

Before you Start:

• Before purchasing any herbicide product it is important to read the label.  The label is the Law.  Carefully review all parts of the label even if you have used the product before.  Select a product that is most appropriate for your site.  If you have questions, ask your vendor before purchasing a product.
• When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times.  If any information provided here contradicts the label, the label takes precedence.  Always follow the label!
• Protect yourself.  Always wear the recommended protective clothing identified on your label.
• When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
• Do not apply during windy or breezy conditions that may result in drift to non-target plants
• Avoid spraying near water.  Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
• Avoid exposure to pets, pollinators, and wildlife.  Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried.
• Avoid spraying blooming plants to minimize any effects to bees and pollinators, and makes applications at times of the day when insects and animals are not active.
• Be sure to store any chemicals, out of the reach of children and pets to keep your family safe.
• Product labels and formulations change regularly.  Check the Pacific Northwest Weed Management Handbook and the product label for current control recommendations.

Herbicides:

The mention of any brand name product is not, and should not be construed as an endorsement for that product.  They are included here only for educational purposes.  Suggested rates are generalized by active ingredient.  Specific rates will vary between products.  Be sure to review the label before application and use the recommended label rate at all times.

Biological:

Tansy ragwort is a great example of biological control success. Three different insects are currently used to target tansy ragwort and have shown to greatly reduce populations in Oregon. While effective, biological control methods will never result in the complete eradication of a weed.  Control of Tansy ragwort using biological controls can also take several years. As such, the use of biological controls should be combined with manual or chemical control methods when working in hay or pasture lands to prevent livestock poisoning. Populations of all biological controls will vary from year to year, so the occasional resurgence of tansy ragwort should be expected, particularly in years with very wet springs.

• Ragwort flea beetle (Longitarsus jacobaeae): The adult form of this insect feeds on the leaves of the tansy ragwort plants. The larvae feed on the roots and the crown of the plants. Adults are small and light brown.  Ragwort flea beetle is the most effective of the biological controls.  Originally introduced in 1971, this species is widespread throughout Clackamas County and redistribution is not necessary.  In years with very wet springs, the impacts of the flea beetle decreases, and alternative control methods may be desired to suppress tansy ragwort populations.
• Ragwort seed fly (Botanophila seneciella syn. Pegohylemia seneciella): The larvae of this insect feed on the seed heads of the tansy ragwort. The white larvae can be found within the seeds from late spring through summer. Adults are small black flies.  Originally released in 1966, this is the rarest and least effective of the biological controls.
• Cinnabar moth (Tyria jacobaeae): The larvae of this insect feeds on the leaves, buds, and flowers of the tansy ragwort. The caterpillars are brightly colored with yellow and black stripes. The adult moth is mostly black with bright red markings on its wings.  Originally introduced in 1960, this species is widespread, and redistribution is generally not needed.  Populations levels fluctuate from year to year and generally lag behind tansy ragwort abundance.

Disposal:

Pulled or dug up plants should be removed from pastures and hay fields.  Plants should be bagged and disposed of as garbage. For large infestations, plants may be removed from the field, piled, and covered in an area inaccessible to livestock.  Care needs to be taken to prevent dispersal of seed, as seeds can develop even after pulling.

Follow-Up:

Tansy ragwort control is manageable. Follow up treatments are necessary and continued monitoring of sites is needed.  Seeds may persist in the soil for years following treatment. If animals have been in a field where tansy is present, isolate animals for a few days to prevent the spread of seeds.

Tansy Ragwort Management Timeline

Best Management Practices:

Small Infestations:

• Consider the land use practices on site.  Identify site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify tansy ragwort.  If you are unsure about a plant bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Plants should be treated using spot spraying techniques in early spring.  Plants may also be pulled by hand or dug up.
• Try not to disturb the soil. Replace any divots created, and work to maintain a healthy vegetative cover to prevent other invasive weed from reestablishing.
• Continue to monitor your site throughout the growing season and for a few years post-treatment. Remove any new growth.

Large Infestations:

• Consider the land use practices on site.  Identify site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify tansy ragwort.  If you are unsure about a plant bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Remove all grazing animals from infested areas.
• Apply herbicide utilizing a spot spray or broadcast application.  Ideally, choose a selective herbicide to minimize the impacts to co-occurring grasses.
• Ensure that biocontrols are present in areas that may not be actively managed.
• Try not to disturb the soil. Replace any divots created, and work to maintain a healthy vegetative cover to prevent other invasive weed from reestablishing.
• Continue to monitor your site throughout the growing season and for a few years post-treatment. Remove any new growth.

Fun Facts:

• Humans can be harmed from tansy ragwort by consuming the plant, consuming livestock suffering from liver damage from tansy ragwort, by consuming animal products such as milk (made from liver damaged cow), and honey (made with tansy ragwort nectar).
• Tansy ragwort has, in the past, been used medicinally. This practice is not recommended due to potential liver damage.
• In ancient times a supposed aphrodisiac was made from Tansy ragwort called satyrion.

Gallery:

Tansy Ragwort Infestation

Mature Tansy Ragwort

Tansy Ragwort Rosette

Tansy Ragwort Flowers and Cinnabar Moth Caterpillar

Cinnabar Moth Caterpillars

Cinnabar moth

Tansy Ragwort Seed Fly

Tansy Ragwort Seed Fly Damage

Tansy Ragwort Flea Beetle

Tansy Ragwort Flea Beetle Larvae

Tansy Ragwort Management

County Agent, Ron Davis, looks at a field of tansy, Clackamas County, ca. 1946

Additional Information:

• Oregon Department of Agriculture: Tansy Ragwort
• Oregon State University Extension: Invasive Weeds in Forest Lands: Tansy Ragwort
• Oregon iMapInvasives: GIST Elemental Stewardship Abstract
• Pacific Northwest Weed Management Handbook: Tansy ragwort
• King County Washington: Tansy ragwort Best Management Practices
• Center for Invasive Species and Ecosystem Health

References:

1. Bossard, C. C., J. M. Randall, & M.C. Hoshovsky.  2000.  Invasive Plants of California’s Wildlands.  Berkeley, CA: University of California Press.  pp 291-295.
2. Christy, J. A., A. Kimpo, V. Marttala, P. K. Gaddis, & N. L. Christy.  2009.  Urbanizing Flora of Portland Oregon 1806-2008.  Native Plant Society of Oregon Occasional Paper 3 pg. 93.
3. DiTomaso, J.M. & E.A. Healy.  2007.  Weeds of California and Other Western State vol 1.  University of California ANR.  pp 382-390.
4. DiTomaso, J.M., G.B. Kyser, S.R. Oneto, R. G. Wilson, S. B. Orloff, L. W. Anderson, S. D. Wright, J.A. Roncoroni, T.L. Miller, T.S. Prather.  2013.  Weed Control in Natural Areas in the Western United States.  Davis, CA: UC Weed Research and Information Center.  pp 438, 446.
5. Kaufman, S. R. & W. Kaufman.  2007.  Invasive Plants: Guide to identification and the Impacts and Control of Common North American Species.  Mechanicsburg, PA: Stackpole Books. pp 145-151
6. King County Noxious Weed Control Program.  2011.  King County Best Management Practices for Controlling Tansy Ragwort (Senecio jacobaea).  https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/BMPs/tansy_ragwort-control.pdf  (Retrieved April 3, 2014).
7. Oregon Flora Project. 2013.  Oregon Plant Atlas: Senecio jacobaea.  https://www.oregonflora.org/atlas.php.  (Retrieved April 3, 2014)
8. Peachy, E., editor.  2014.  Pacific Northwest Weed Management Handbook: Control of Problem Weeds.  (Retrieved April 3, 2014).
9. Macdonald, C., & M. Russo. 1989.  Elemental Stewardship Abstract for Tansy Ragwort, (Senecio jacobaea). The Nature Conservancy.  https://www.invasive.org/gist/esadocs/documnts/senejac.pdf  (Retrieved April 3, 2014)
10. Boersma, P.D., Reichard, S.H. & Van Buren, A.N. (Eds.). 2006.  Invasive species in the Pacific Northwest. Seattle: University of Washington Press pp.

Common name:

Canada thistle, Canadian thistle, corn thistle, creeping thistle

Scientific Name:

Cirsium arvense (syns. Breea arvensis, Carduus arvensis, Cirsium incanum, Cirsium orchrolepideum, Cirsium setosum, Cnicus arvensis)

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class C
• 4-County CWMA: Class C
• Columbia Gorge CWMA: Class C

Description:

General:

Canada thistle is a tall, prickly, creeping rhizomatous perennial with multiple purple flowers. The erect plant stands around 2 to 4 feet tall on rigid, hairy, branched stems that usually die back during winter. This aggressive noxious plant forms dense unisex patches on disturbed land, and produces allelopathic chemical that inhibit growth of other plants.  Canada thistle is native to Europe, not Canada, and can be found throughout the United States.

Leaves:

Canada thistle leaves are oblong to lanceolate or lance-shaped, 2 to 7 inches long with deep and irregular lobes. Leaves are toothed with prickles that are 3 to 6 mm long. The green leaves are slightly hairy on their upper surface. Canada thistle leaves are alternate and are attached directly to the stem; do not have a leaf stem. Young leaves also alternate but are oval-shaped with no point, teethed with a softened prickle.

Flowers

The purple disk flowers of the Canada thistle plant are surrounded by rows of soft spine-tipped phyllaries. Flowers appear from June to October with 1 to 5 heads per branch. Petals are often purple but can be pink or even white. Both sexes have umbrella-shaped flowers, with female flowers being slightly bigger with longer pappus (male 10-14 mm, female 14-20 mm).

Fruits

Canada thistle has dry, small, single seed fruit called achenes. Oval, slightly curved, hairy and shiny; the achenes have feathery pappus attached at the base. Both the achenes (2-4 mm long) and the pappus bristles (12-20mm) are tan.

Roots

Canada thistle has a deep and extensive root system consisting of vertical and several horizontal roots extending as far as 15 feet. Roots are rhizomatous, with new stems sprouting in spring.  Roots are stiff and fragile but long-lived. In a years time, one plant’s root system can take over an area up to 25 ft². Seedlings start with deep taproot with creeping rhizomes developing between 2 and 4 months.

Reproduction:

Canada thistle reproduce both by seed and vegetatively through creeping roots. March through April, Canada thistle seeds germinate and grow to form rosettes. New plants can develop from underground shoots and roots longer than 1 cm. In May, new shoots bolt. June through August the plant flowers with seed production starting in August and continuing throughout September. Female flowers need to be pollinated to produce viable seeds which take 8-10 days to develop.  Plants produce 1,000 seeds on average and may produce up to 5,300 seeds. Seeds are dispersed by the wind.

Seeds are transported mostly by wind. The Canada thistle plant returns to the rosette stage near October and November.  Flower stems usually stay up for some time after seed reproduction. New root and shoot buds develop over winter.

New plants developed from vegetative reproduction are hardy, not sensitive to competition. New plants developed from seeds are slow-growing and sensitive to both competition and shading.

The seeds may remain viable in the soil for over 20 years.

Habitat:

Canada thistle can be found in disturbed areas with abundant sun and moist but not wet soils. Crop fields, forest openings, gardens, hillsides, logged areas, pastures, range land, roadsides, stream banks, vacant lots and waste places  are the usual infestation locations for Canada thistle. It is found throughout most of the continental United States.

Impacts:

• Canada thistle spreads quickly and forms dense infestations
• Reduces crop yields and pasture productivity
• Competes with and replaces native vegetation
• Reduces animal diversity
• Host plant for several crop-damaging insects

Introduction:

Canada thistle was introduced to the Willamette Valley between 1875 and 1899. Although it was reported to be not common when first collected, it is now very common throughout the area.

Distribution:

Clackamas County:

Canada thistle can be found throughout Clackamas County.  It is widespread and directly impacts properties throughout the county.  As an ubiquitous weed, this is not a species that is actively surveyed and the mapped distributions do not represent the full extent of the Canada thistle population in Clackamas County.

State of Oregon:

• Oregon iMapInvasives
• Oregon Weedmapper
• Oregon Flora Plant Atlas

United States:

• EDDMapS
• USDA Plants Database

Management:

Strategy:

The management of invasive weeds is best served through a process know as Integrated Pest Management (IPM).  IPM is a weed management methodology that utilizes:

• Management thresholds to determine when and if to initiate control,
• The ecology and life history characteristics of the targeted invasive weed,
• Site-specific conditions and land use considerations to inform management practices,
• The effectiveness and efficiency of various control methods.

An IPM based strategy ensures the maximum effectiveness of treatment measures.  IPM strategies typically use more than one management method to target one or more susceptible life stages.  It is adaptive to site conditions in the field and to the response of a plant to management.  The utilization of multiple management tools also inherently reduces the use of herbicides in a management plan.   The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a weed particular infestation.

Manual:

Only young plants can be removed by digging up the roots. More developed infestations have deep rhizomatous roots that greatly complicate removal. Any remaining root fragments can produce new plants. Do not compost flower heads, seeds or rhizomes as most home compost piles do not reach a temperature sufficient to kill all seed.

Mechanical:

Mowing can help te reduce the nutrients stored in the plants, but to be effective mowing must be repeated every few weeks for several growing seasons. Mowing can be an important tool, especially when combined with other management practice such as herbicide application.

Tillage increases Canada thistle infestations.  Rhizomes are cut and spread, allowing new plants to grow. Tillage can be effective in combination with chemical treatments.

Cultural:

Burning and grazing are not effective controls for Canada thistle management. Burning may reduce seed production.

Solarization of patches using plastic sheeting can be successful in controlling seedlings and small plants.

Chemical:

Herbicide application is an effective means to control Canada thistle infestations. Canada thistle is susceptible to several systemic herbicides. Be cautious when using herbicides on pasture land with grazing animals.

Before you Start:

• Before purchasing any herbicide product it is important to read the label.  The label is the Law.  Carefully review all parts of the label even if you have used the product before.  Select a product that is most appropriate for your site.  If you have questions, ask your vendor before purchasing a product.
• When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times.  If any information provided here contradicts the label, the label takes precedence.  Always follow the label!
• Protect yourself.  Always wear the recommended protective clothing identified on your label.
• When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
• Do not apply during windy or breezy conditions that may result in drift to non-target plants
• Avoid spraying near water.  Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
• Avoid exposure to pets, pollinators, and wildlife.  Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried.
• Avoid spraying blooming plants to minimize any effects to bees and pollinators, and makes applications at times of the day when insects and animals are not active.
• Be sure to store any chemicals, out of the reach of children and pets to keep your family safe.
• Product labels and formulations change regularly.  Check the Pacific Northwest Weed Management Handbook and the product label for current control recommendations.

Herbicides:

The mention of any brand name product is not, and should not be construed as an endorsement for that product.  They are included here only for educational purposes.  Suggested rates are generalized by active ingredient.  Specific rates will vary between products.  Be sure to review the label before application and use the recommended label rate at all times.

Biological:

Several different insects are have been used to target Canada thistle populations in Oregon. While effective in reducing infestations, biological control methods will never result in the complete eradication of a weed. Populations of all biological controls will vary from year to year.

• Canada thistle stem weevil larvae (Hadroplontus litura) mine the pith in stems of bolting plants. The adults feed on leaves causing minor damage.  This biological control was first released in 1981 and is now established in most eastern Oregon counties. The weevil is becoming more widespread but is still difficult to collect. The weevil does not seem to thrive in western Oregon.
• Thistle stem gall fly larvae (Urophora cardui) were specifically released in the United States to control Canada thistle. Larvae gall stems, which act as nutrient sinks, occasionally reducing seed production or plant height.
• The Canada thistle rust fungus (Puccinia punctiformis) was introduced into Oregon in 2018 to control Canada thistle. Spores germinate on leaves, travel down stems, and systemically infect the root system as a cryptic root parasitic fungus. The rust fungus often limits an infestations ability to increase and, in some cases, causes infestations based on one or two mother plants to experience colony collapse

Disposal:

Canada thistle flowers and seeds should be collected and put in trash or yard waste. Do not compost flowers and seeds. Non-flowering plants can be chopped up and composted or put in trash or yard waste.

Follow-Up:

Follow-up treatments are often necessary to control large infestations.

Best Management Practices:

Small Infestations:

• Consider the land use practices on site.  Identify, and site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify Canada thistle.  There are several native thistle look-a-likes.  If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize and negative impact on them.
• Dig individual plants or very young infestations.  Carefully remove any rhizomatous roots to prevent resprouting.
• Lay sheet plastic over infestations to solarize small and young plants.
• Spot spray Canada thistle plants using one of the recommended products labeled for use in your area.  Applying a directed spray of glyphosate or clopyralid at the flower bud stage before flowering, or in the fall before the first frost will control Canada thistle. Generally, fall treatments are more effective than spring treatments.  Clopyralid provides the best and most consistent control. Metsulfuron, aminopyralid or triclopyr products are also effective. You may need to repeat herbicide applications for several years.

Large Infestations:

• Consider the land use practices on site.  Identify, and site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify Canada thistle.  There are several native thistle look-a-likes. If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize and negative impact on them.
• Spot or broadcast spray Canada thistle plants using one of the recommended products labeled for use in your area.  Apply a directed spray of glyphosate or clopyralid at the flower bud stage before flowering, or in the fall before the first frost will control Canada thistle. Generally, fall treatments are more effective than spring treatments.  Clopyralid provides the best and most consistent control. Metsulfuron, aminopyralid or triclopyr products are also effective. You may need to repeat herbicide applications for several years.
• Mow or tilling populations can stimulate regrowth which may accelerate follow-up chemical control treatments.
• Revegetate sites by seeding competitive cover and prevent re-establishment.  Grasses can be an effective competitor and allow for the use of selective herbicides.

Fun Facts:

• Canada thistle is an excellent pollinator plant supplying nectar to bees for honey.
• Canada thistle has male and female flowers
• Leaves can be chewed to relieve a tooth ache.
• Roots are edible but often cause flatulence.
• Plants host agricultural pests such as sod-web worm, bean aphid, stalk borer, and cucumber mosaic virus.

Gallery

Canada thistle seedling

Canada thistle rosette

Canada thistle stems

Canadian thistle leaf

Canada thistle flowering plants

Large infestation of Canada thistle

Canada thistle flowers

Canada thistle inflorescence

Canada thistle flowering plants

Large infestation of Canada thistle

Canada thistle plant seeding

Canadian thistle pappus

Canadian thistle flower heads

Canadian thistle flowers

Canada thistle seeds

Additional Information:

• ODA Noxious Weed Profile
• Washington State Noxious Weed Control Board
• Oregon State University Extension: Canada Thistle 
• Pacific Northwest Weed Management Handbook: Canada Thistle Control
• Weed Research & Information Center: Canada Thistle Weed Report
• Columbia Gorge CWMA: Canada thistle BMP
• King County Washington: Canada Thistle Fact Sheet
• Center for Invasive Species and Ecosystem Health: Canada Thistle
• Invasive Species Compendium: Canada thistle Datasheet

References:

1. DiTomaso, J.M., G.B. Kyser, S.R. Oneto, R. G. Wilson, S. B. Orloff, L. W. Anderson, S. D. Wright, J.A. Roncoroni, T.L. Miller, T.S. Prather.  2013.  Weed Control in Natural Areas in the Western United States.  Davis, CA: UC Weed Research and Information Center.  pp 119-121.
2. Bossard, C. C., J. M. Randall, & M.C. Hoshovsky.  2000.  Invasive Plants of California’s Wildlands.  Berkeley, CA: University of California Press.  pp 106-111.
3. Kaufman, S. R. & W. Kaufman.  2007.  Invasive Plants: Guide to identification and the Impacts and Control of Common North American Species.  Mechanicsburg, PA: Stackpole Books. pp 301-303.
4. King County Noxious Weed Control Program.  2011.  King County: Canada Thistle Fact sheet.  https://your.kingcounty.gov/dnrp/library/water-and-land/weeds/Brochures/CanadaThistle_factsheet.pdf  (Retrieved Jan. 7, 2015).
5. Oregon Flora Project. 2013.  Oregon Plant Atlas: Cirsium arvense.  http://www.oregonflora.org/atlas.php .  (Retrieved May 22, 2013)
6. Peachy, E., D. Ball, A. Hulting, T. Miller, D. Morishita, P. Hutchinson. eds.  2019.  Pacific Northwest Weed Management Handbook: https://pnwhandbooks.org/weed/other-items/control-problem-weeds/thistle-canada-cirsium-arvense-selective-control-crops (Retrieved Aug 30, 2019).

Common names:

English Ivy

Atlantic ivy or Irish ivy

Scientific Name:

Hedera helix (syns. Hedera helix ssp. helix, Hedera canariensis, Hedera helix ssp. canariensis)

Hedera hibernica (syns. Hedera helix ssp. hibernica)

Noxious Weed Listing:

• WeedWise: Maintenance
• State of Oregon: Class B
• State of Washington: Class C
• 4-County CWMA: Class C
• Columbia Gorge CWMA: Class B

Description:

General:

English ivy is an evergreen climbing vine in the Araliaceae (Ginseng) family.  It has historically been a common garden ornamental and has more than 400 cultivars.  It has escaped cultivation to become highly invasive in forests and natural areas throughout the Pacific Northwest.  Native to Europe, these plants are characterized by long viny stems reaching up to 30 m in length, with aerial, clinging small roots. English ivy damages desirable vegetation by shading out and smothering plants.  English ivy also covers trees making them more susceptible to wind damage due to the additional weight of the ivy in the trees as well as the additional drag of the evergreen leafy vines.  English ivy has two distinct growth forms: a juvenile form, that is characterized by rapid clonal and vegetative growth, and a mature form characterized by flowering and berry production.

In Oregon, three Hedera species have been documented: English ivy (H. helix), Atlantic ivy (H. hibernica), and Persian ivy (H. colchica). However, only H. helix and H. hibernica are listed as noxious weeds in Oregon. The invasive plant commonly referred to as English ivy is actually comprised of both H. helix and H. hibernica. Identification and differentiation between the species are complicated because of there many cultivated varieties. Both H. helix and H. hibernica have been commonly sold as English ivy, but can be differentiated by leaf shape and tiny hairs on the young leaves. These two species can also be differentiated through genetic testing.

Leaves:

The leaves come in two forms: juvenile and mature.  Both leaves are evergreen, leathery, and palmately shaped. Juvenile leaves have 3-5 lobes and are slightly hairy.  Generally, the lobes on H. helix are deeper than H. hibernica, but the lobes can vary. The leaves of mature ivy are ovate to diamond-shaped, unlobed or slightly lobed, darker green and more leathery. On both growth forms, the leaves alternate along the vines and are up to 10 cm long. Leaves can be toxic to humans and cattle if ingested.  Leaves can also cause contact dermatitis in sensitive individuals.

Flowers

English ivy generally will only flower under conditions with adequate light and optimal nutrients.  Flowers are only produced high in the tree canopy within infested forests, or along steep slopes.  English ivy flowers in the fall and are pollinated by insects.  Adult plants flower in clusters. The flowers are five-petaled, greenish to white in coloration and are only 3-5 mm long.

Fruits

Fruits develop as fleshy, dark blue to black berries that ripen in spring.  Thousands of fruits can be produced by an adult plant each year.  English ivy berries, particularly when underdeveloped, can be toxic to humans and cattle if ingested. These fruits are 5-10 mm in size and hold 1-3 seeds. Approximately 70% of the seeds produced are viable.

Roots

The juvenile English ivy plants have adventitious roots at their nodes.  Roots are generally shallowly rooted, but robust.  English ivy also forms aerial, clinging rootlets, allowing it to adhere and climb vertically.  Adult English ivy plants form a woody base.

Reproduction:

English ivy reproduces both from mature seeds as well as from root-like stems and sprouting fragments.  The berries of English ivy are ingested by birds and the seeds can be dispersed great distances from parent plants. New plants can regenerate from stems and fragments from both the mature and juvenile growth forms. Regenerating plants maintain the growth form of their parents, such that plants formed from stem regeneration of adult form plants will keep adult characteristics.  Once established juvenile plants can live up to 10 years before reaching maturation.   English ivy plants can live up to 100 years or longer with one plant in England being documented at more than 400 years in age.

Habitat:

The areas most infested by English ivy are urban natural areas, disturbed forests, woodlands, and along stream corridors.  Plants grown in moist soils with summer shade and winter sunlight will flourish.  Urban forest and natural areas are especially impacted as a result of repeated reinfestation from garden escapees.

Impacts:

• Weighs down and harms large canopy trees making them more susceptible to wind throw
• Smothers and displaces forest floor vegetation.
• Degrades wildlife habit and reduces the diversity of animals in infested areas.
• Toxic berries and leaves can cause injury.
• Very invasive with rapid and intense vegetative growth, that can quickly transform a site.
• Seeds disperse great distances, making containment of infestations very difficult.
• Can be a reservoir for bacterial leaf scorch harmful to elms, oaks, and maples.
• Vines tangle among native understory making removal difficult.
• Increases erosion due to the displacement of native species and a shallow root system.

Introduction:

The original introduction of English ivy to the United States is believed to have been by European immigrants during colonial times as a garden ornamental. The earliest record of English ivy in North America dates to 1727.  Introduction to the Portland area occurred between 1875 and 1899 (Christy et al., 2009).

Distribution:

Clackamas County:

English ivy can be found throughout Clackamas County.  It is very widespread and directly impacts properties throughout the county.  As a ubiquitous weed, this is not a species that is actively surveyed and the mapped distributions do not represent the full extent of the English ivy population in Clackamas County.

State of Oregon:

• Oregon iMapInvasives
• Oregon Weedmapper
• Oregon Flora Plant Atlas

United States:

• EDDMapS
• USDA Plants Database

Management:

Strategy:

The management of invasive weeds is best served through a process known as Integrated Pest Management (IPM).  IPM is a weed management methodology that utilizes:

• Management thresholds to determine when and if to initiate control,
• The ecology and life history characteristics of the targeted invasive weed,
• Site-specific conditions and land use considerations to inform management practices,
• The effectiveness and efficiency of various control methods.

An IPM based strategy ensures the maximum effectiveness of treatment measures.  IPM strategies typically use more than one management method to target one or more susceptible life stages.  It should be adaptive to site conditions in the field and to the response of a plant to management.  The utilization of multiple management tools inherently reduces the use of herbicides in a management plan.  The IPM process ultimately provides a framework for the establishment of Best Management Practices (BMP) which outlines the best approach for controlling a weed particular infestation.

Manual:

English ivy is often best controlled using manual control methods.  The waxy leaves of English ivy and its ability to regenerate from stems and fragments, make it resistant to chemical and mechanical control methods.  While effective the removal of English ivy can be time-consuming and labor-intensive.  As such, persistence is possibly the most important factor in determining the success of your treatments.  It has been suggested that an acre of English ivy dominated forest requires more than 300 man-hours for an initial clearing and continued maintenance to restore a site. So restoration efforts should plant their work accordingly

The first step is to choose an area, that can receive repeated control efforts.  Prioritize your site.  Choose a portion of your management area that is of highest priority, or work from a relatively intact area, and slowly expand your treatments systematically outward.  Look at the concentration and location of the ivy, the landscape, soil moisture, abundance of native plants in the area as well as the number and skill of workers assisting.  Before handling English ivy be sure to wear long sleeves, long pants, and gloves to protect yourself from potential dermatitis.  Utilize tools such as shovels, rakes, mattocks, and weed wrenches to assist in the removal of the roots.  Saws, loppers, and hand clippers can be used to cut vines.

In locations where native plants are abundant, the preferred practice is hand removal.  Vines growing on trees should be targeted first to prevent flowering and seed set and to preserve canopy trees on site.  Vines on trees should be cut using a saw, loppers or hand clippers around the entire base of the tree and also at a comfortable arm reach then removed from the tree. Leave the remaining ivy above the cut line to dry out and fall down on its own.  All ivy should be removed within, a minimum of 3 feet around the trunk to better protect the tree.  Flowering or seeding plants should be removed to prevent seeding or regeneration.  For ground ivy control should focus on one location, pulling every vine and root up within reaching distance, before moving to a new location.  Working systematically from a core area.   Manual control of English ivy is best done in the fall and winter when the ground is soft and plants are not seeding.

When few native plants reside on the property and there are sufficient workers, English ivy can be removed in large mats using a technique called the ‘Log Roll’.  This technique relies upon first defining a treatment area.  The perimeter of the area is cut and a line of workers pull the edge of the mat, rolling vines and roots of the ivy on top of itself. It is important to shake the roots to remove soil.  The roll should then be mulched in place to prevent resprouting.  Workers should also follow up in the cleared site to remove any missed roots. This practice can be done on both flat ground and on hillsides. Soils with higher water content allow for an easier pull.

Additional tips to reduce erosion and minimize damage to native plants:

• Remove as much of the root system as possible by pulling the vine directly where the root comes out of the ground
• Minimize trampling and churning of the soil
• Protect native plants that are present through careful and conscientious pulling and walking
• Be thorough, by completely clearing an area before moving on

Mechanical:

English ivy can be mowed or cut but this is generally not recommended due to its ability to regenerate following cutting.

Cultural:

Grazing has been used to defoliate large infestations of English ivy.  Goats and sheep will graze the ivy leaves, but plants will readily resprout following grazing.  As such, grazing animals must be rotated repeatedly back onsite to suppress regrowth.  English ivy is generally not favored by grazing animals, so co-occurring native plants are usually grazed more strongly than the ivy itself.  As such, grazing is generally considered to be ineffective, or of limited use.  Mature ivy plants are also generally found growing above the browse line, so manual removal of tree ivy is required in conjunction with any grazing strategy.

English ivy is fire resistant and doesn’t carry a fire well.    The repeated torching of ivy plants will cause cellular damage and dieback.  With persistence, this method will exhaust nutrients as the English ivy resprouts, but it is generally inefficient compared to other methods.  As such this method is generally not recommended.

Chemical:

Effective chemical control of English ivy is dependent on a few variables including timing, sensible application, and the proper mixture of chemicals. The timing is important to limit damage to native plants. Herbicide application during dry and sunny periods in late winter can be an effective chemical control on English ivy. The ivy is still alive and may still be growing in the winter while most native plants are dormant and protected.  Herbicide has shown to be successful when applied directly to cut stems specifically around a tree trunk.

Foliar application of herbicides is deterred by the waxy coating on the leaves. This is especially true for older/mature leaves and application during the growing season.  This leads to runoff of herbicide onto nearby native plants.  A fatty acid can be applied before or with the herbicide application to increase absorption into the leaves.

Widespread chemical control of English ivy is not suggested and should only to be considered in areas completely dominated by ivy or on difficult sites were manual control methods may be impractical or dangerous.

Before you Start:

• Before purchasing any herbicide product it is important to read the label.  The label is the Law.  Carefully review all parts of the label even if you have used the product before.  Select a product that is most appropriate for your site.  If you have questions, ask your vendor before purchasing a product.
• When selecting herbicides always use a product appropriately labeled for your site. Follow label recommendations and restrictions at all times.  If any information provided here contradicts the label, the label takes precedence.  Always follow the label!
• Protect yourself.  Always wear the recommended protective clothing identified on your label and shower after use.
• When applying herbicides use spot spray techniques whenever possible to avoid harming non-target plants.
• Do not apply during windy or breezy conditions that may result in drift to non-target plants
• Avoid spraying near water.  Hand-pull in these areas, to protect aquatic and riparian plants and wildlife.
• Avoid exposure to pets, pollinators, and wildlife.  Remove animals from treatment areas to avoid exposure to herbicides. Follow the reentry instructions on your herbicide label and keep pets out of the area until the herbicides have dried and it is safe to return.  Avoid spraying when insects and animals are active.  Avoid spraying blooming plants to minimize any effects on bees and other pollinators.
• Be sure to store any chemicals out of the reach of children and pets to keep your family safe.
• Product labels and formulations change regularly.  Check the Pacific Northwest Weed Management Handbook and the label for current control recommendations.

Herbicides:

The mention of any brand name product is not, and should not be construed as an endorsement for that product.  They are included here only for educational purposes.  Suggested rates are generalized by active ingredient.  Specific rates will vary between products.  Be sure to review the label before application and use the recommended label rate at all times.

Biological:

There are no effective biological control agents available for English ivy.

Disposal:

There are many ways to dispose of English ivy when clearing your property. For small infestations, bagging up pulled plants is the best practice if possible.  For larger infestations, pile up the debris and let it dry out.  Placing a tarp under the pile will help prevent resprouting.  Piles can also be covered to speed up drying and decompositions.  Large debris piles can create dead spots, so placement of piles should be placed to minimize the impact to desirable vegetation.  Under dry conditions, plants can be chopped into a mulch and spread over the area for ground cover and nutrients, but be careful with this method as covering the ground will reduce the visibility of missed/live roots.

Follow-Up:

Diligence is the most important aspect of controlling English Ivy.  Ivy plants will readily resprout from any roots left remaining, so repeated follow-up is required. An herbicide application in summer has shown to be the most effective after treatment. Re-treatment may be required to achieve effective control.  The seed may persist in the soil for years following treatment or arrive on-site from adjacent and nearby infestations.

Best Management Practices:

Monoculture Infestations:

• Consider the land use practices on site.  Identify, any site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify English ivy.  If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• Herbicide application is often the best approach with respect to cost, time, and erosion protection for large ivy infestations with few desirable plants.
• Winter applications have shown to be effective while minimizing the impact to native, but spray only during when winter weather is above 55 F, and no precipitation is expected for at least three days.  Otherwise, plan treatments for late summer.
• Follow-up treatments 6-12 months afterward can be as re-treatment of herbicide, spot spray herbicide application or spot manual removal.
• Replant site with site-appropriate native vegetation as soon as possible. Grass seed can be spread to stabilize soil in between removal and plantings.
• Continue to monitor the site for regrowth and treat any new infestations.

Small Infestations within native or desirable vegetation:

• Consider the land use practices on site.  Identify, any site-specific considerations that should be taken into account before initiating control.
• Be sure you can properly identify English ivy.  If you are unsure about your weed bring a sample to the Conservation District, and we can help to identify your particular weed.
• Identify any native or desirable plants nearby, and take precautions to minimize any negative impact on them.
• A manual approach is best with a limited spot spray application of herbicide in dense patches within native vegetation.
• Pull plants in winter and spring when the soil is moist and the ivy is prominent.
• Replanting is not as necessary in small infestations within native vegetation because the natives will expand into open areas. If large gaps are present, additional plantings may be beneficial.
• Continue to monitor the site for regrowth and treat any new infestations as they occur.

Fun Facts:

• Juvenile plants can climb as much as 30 ft per year.
• Leaves and berries have been eaten as an expectorant.
• A leaf reduction can be used to restore dark fabrics or dye hair and twigs can create yellow and brown dye.
• Medicinally used since ancient times to treat rheumatism, toothache, bronchitis, and many skin problems including burns, infections, and cellulite.
• Ivy has been long used in England as decorations during the Christmas season.

Gallery:

English ivy

Tree ivy infestation

English Ivy

English ivy flowers

English ivy berries

English Ivy seedling

English ivy in trees

Massive English Ivy Stem

English ivy after treatment

Additional Information:

• Oregon Department of Agriculture: English ivy
• English ivy is an invasive weed in the Pacific Northwest
• Oregon State University Extension: Invasive Weed in Forest Land: English ivy
• Controlling English ivy in the Pacific Northwest
• Pacific Northwest Weed Management Handbook: English ivy
• King County Washington: English ivy Weed Bulletin
• Center for Invasive Species and Ecosystem Health
• No Ivy League
• Weed Research & Information Center: English Ivy Weed Report
• Invasive Species Compendium: English Ivy Datasheet

References:

1. Bossard, C. C., J. M. Randall, & M.C. Hoshovsky.  2000.  Invasive Plants of California’s Wildlands.  Berkeley, CA: University of California Press.  pp 277-281.
2. Christy, J. A., A. Kimpo, V. Marttala, P. K. Gaddis, & N. L. Christy.  2009.  Urbanizing Flora of Portland Oregon 1806-2008.  Native Plant Society of Oregon Occasional Paper 3 pg. 218.
3. DiTomaso, J.M. & E.A. Healy.  2007.  Weeds of California and Other Western State vol 2.  University of California ANR.  pp 1426-1434.
4. DiTomaso, J.M., G.B. Kyser, S.R. Oneto, R. G. Wilson, S. B. Orloff, L. W. Anderson, S. D. Wright, J.A. Roncoroni, T.L. Miller, T.S. Prather.  2013.  Weed Control in Natural Areas in the Western United States.  Davis, CA: UC Weed Research and Information Center.  pp 341-343.
5. Holloran, P., A. Mackenzie, S Farrell, D. Johnson.  2004.  The Weed Workers Handbook: A Guide to Techniques for Removing Bay Area Invasive Plants.  Berkeley, CA: California Invasive Plant Council.  pp 60-61
6. Kaufman, S. R. & W. Kaufman.  2007.  Invasive Plants: Guide to identification and the Impacts and Control of Common North American Species.  Mechanicsburg, PA: Stackpole Books. pp 145-151
7. King County Noxious Weed Control Program.  2011.  English ivy identification (Hedera helix).  https://www.kingcounty.gov/environment/animalsAndPlants/noxious-weeds/weed-identification/english-ivy.aspx  (Retrieved Jan 21, 2014).
8. Oregon Flora Project. 2013.  Oregon Plant Atlas: Hedera helix.  http://www.oregonflora.org/atlas.php.  (Retrieved Jan 21, 2014)
9. Peachy, E., D. Ball, A. Hulting, T. Miller, D. Morishita, P. Hutchinson. eds.  2013.  Pacific Northwest Weed Management Handbook: Control of Problem Weeds.  (Retrieved Jany 21, 2014).
10. Soll, J. 2004.  Controlling English Ivy (Hedera helix) in the Pacific Northwest. The Nature Conservancy.  https://www.invasive.org/gist/moredocs/hedhel02.pdf   (Retrieved Jan 21, 2014)