If you start looking around Clackamas County, it won’t take you long to find the invasive tree-of-heaven (Ailanthus altissima). This state-listed noxious weed is increasingly more common in many of our urban areas where it flourishes. Tree-of-heaven seems right at home in alleys, roadsides, railways, vacant lots, that crack in the sidewalk. Very large trees […]
tree-of-heaven, stinking sumac, stinking quassia, copal-tree, Chinese sumac, varnish tree
Ailanthus altissima
Tree-of-heaven is an introduced deciduous tree species that can grow up to 80 feet tall and six feet in diameter. It has large pinnately compound leaves. Plants are dioecious (male or female) with females producing copious seeds each season.
It is seen in diverse locations across our region but is most commonly seen growing in urban areas, where it was once intentionally introduced. Vast numbers of seedlings, saplings, and suckering plants can be seen growing near larger parent trees. The bark on young trees is smooth and green. As it ages, the bark turns gray and develops shallow, diamond-shaped fissures. The green to brown branches grow alternately on the tree and have a pithy, brown center. The branches are also pock-marked with a V-shaped or heart-shaped leaf scars.
Leaves are pinnately compound, meaning they have leaflets attached on each side of a central stem. Leaflets have mostly smooth edges with one to two protruding bumps at the base called glandular teeth. When crushed, the leaves can have a rancid peanut butter-like odor.
Male and female flowers form in terminal clusters on separate trees. Flower clusters may be up to 12 inches wide and are largest on male trees. Tiny individual flowers are light green to pale.
In late summer through autumn, tree-of-heaven produces large clusters of papery winged fruit known as samaras. Each fruit contains a single central seed. The samaras vary from greenish-yellow to red-brown and are often vibrantly colored in the fall.
Tree-of-heaven produces a long taproot and suckers freely when cut, making it difficult to control. Creeping roots may extend outward up to 50 feet in all directions.
Tree-of-heaven can be easily confused with other trees that have compound leaves with many leaflets, such as sumac or walnut. The leaf edges of the look-alikes typically have teeth or serrations, while those of tree-of-heaven are smooth.
This weed reproduces both by seed and vegetatively through sprouting roots. New shoots can sprout as far as 50 feet away from the parent tree. One tree can produce over 300,000 seeds annually, which are then dispersed by water, wind, and birds. Cut stems can form roots when left on moist ground.
Tree-of-heaven grows in a variety of habitats and is commonly found in disturbed areas along forest edges, roadsides, fence rows, urban parks, old fields, and railroad embankments. It is tolerant of full sun to part shade, many types of pollution, and poor soil conditions. It can grow in many harsh environments, including pavement cracks and building foundations!
Tree of heaven has been known to cause skin irritations or allergies in some people. Additionally, there have been rare reports of myocarditis (inflammation of the heart muscle) from exposure to sap through broken skin. People who work around the tree should wear personal protective equipment, including eyewear and gloves.
The first documented appearance of tree-of-heaven in Oregon can be found in local herbaria dating back in 1904, in Wasco County. The plant is native to China and was commonly introduced as an ornamental plant before escaping cultivation. It is believed to have been introduced sometime between 1875 and 1899.
Tree-of-heaven is found throughout much of Clackamas County. As a common weed, this is not a species that is actively surveyed. The mapped distributions do not represent the full extent of tree-of-heaven in Clackamas County.
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:
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 removal of tree-of-heaven can be an effective control option for seedlings and small samplings, but it is labor-intensive. Plants can be pulled when the soil is moist to ease the removal of the roots and to put less strain on the worker. All plants and roots need to be removed to prevent regrowth. A weed wrench, shovel, or hoe can be used to assist with root removal. Sites should be monitored for regrowth regularly to ensure complete control. Once plants become too large and develop a strong root system other control methods will be required.
While manual removal can be an effective treatment, it can cause heavy soil disturbances on site. Soil disturbance can bring tree-of-heaven seeds to the surface creating a new generation of growth. Minimize soil disturbance and re-vegetate disturbed areas to prevent further infestations.
Cutting tree-of-heaven is not effective and should be avoided. Cutting can stimulate the suckering of new shoots, especially in larger specimens. A hack-and-squirt, or similar herbicide treatment (see below) will need to be utilized to control suckering and continued growth following cutting.
The cutting of a large tree-of-heaven is ineffective on its own. Cut trees will lead to significant resprouting from roots. As a result, cutting and removal of well-established trees should only be incorporated after trees have received a prescribed herbicide treatment. Chain saws are typically used to fell dead or dying tree-of-heaven following herbicide treatments. Large specimens can pose a risk to people and property. Whenever you are working in sensitive areas, you should coordinate removal activities with a licensed arborist.
Tree-of-heaven does not compete well in heavily shaded areas. Competitive plantings can help to minimize the impacts of tree-of-heave and prevent establishment.
Chemical control is an effective tool to control large trees and dense infestations. Tree-of-heaven is susceptible to several systemic herbicides. Plants should be treated using foliar treatments, basal bark, hack, and squirt, or cut stump methods. Chemical control options are frequently used in conjunction with other control practices within a broader IPM framework.
Product Names: Accord, Aquamaster, Rodeo, Roundup, and various others (glyphosate) + Garlon 3a, Element 3a, Vastlan (Triclopyr)
Rate:
Foliar treat: use glyphosate at 3 qts/acre with triclopyr at 1.5 – 2qts/ac, plus a non-ionic surfactant.
Time: Foliar applications should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. This mixture is not selective and will harm grasses and other desirable vegetation. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control.
Product Names: Accord, Aquamaster, Rodeo, Roundup, XRT II, and various others
Rate:
Foliar treat: use 2.0% to 4.0% v/v solutions, plus 0.5% v/v non-ionic surfactant.
Hack and Squirt: apply 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Glyphosate is not selective and will harm grasses and other desirable vegetation. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Cut stems horizontally at or near ground level and immediately apply herbicide.
Product Names: Garlon 4 (triclopyr ester), Garlon 3A, Element 3A (triclopyr amine), Pathfinder II, Vastlan
Rate:
Foliar treat: 1.0% to 2.0% v/v solution, plus 0.5% v/v non-ionic surfactant.
Hack and Squirt: make 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Basal Bark: use 20%-30% v/v in 70%-80% oil carrier.
Cut Stump: use 20%-25% v/v solution.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Triclopyr is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Triclopyr ester formulations may volatilize under warm temperatures. Expect root suckering following cut stump treatments.
Product Names: Vanquish, Banvel
Rate:
Foliar treat:5.0% v/v solution, plus 0.5% v/v non-ionic surfactant.
Cut Stump: use 25%-50% v/v solution.
Time: Foliar application and cut stump treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Dicamba is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Dicamba formulations volatilize under warm temperatures. Expect root suckering following cut stump treatments.
Product Names: Capstone
Rate:
Foliar treat: 1.0% to 1.5% v/v solution, plus 0.5% v/v non-ionic surfactant.
Time: Foliar application treatments should be carried out in summer or early fall.
Comments: Re-treatment may be required to achieve effective control. Triclopyr + aminopyralid is selective and will not harm grasses but will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Formulations may volatilize under warm temperatures.
Product Names: Arsenal, Habitat, Stalker, Chopper, Polaris
Rate:
Foliar treat: 1 to 2% v/v solution plus 0.25 to 0.5% surfactant v/v
Cut stump: 20% v/v solution in water plus 80% oil or water carrier, depending on product used.
Hack and Squirt: make 1 cut for every 3 inches of stem diameter, and apply 1 ml of undiluted herbicide to each cut.
Basal Bark: use 20% in 80% oil carrier.
Time: Foliar application and Hack and squirt treatments should be carried out in summer or early fall.
Comments: Imazapyr is a soil residual herbicide and may result in bare ground around plants after treatment.
Product Names: Escort
Rate:
Foliar treat: 2 oz per acre
Time: Foliar application treatments should be carried out in summer or early fall.
Comments: Can be tank-mixed with glyphosate or triclopyr
There are no approved biological agents available at this time. Current research is underway to determine the suitability of three fungal pathogens and two insects to help control tree-of-heaven.
Small tree-of-heaven plants that have not gone can be disposed of in yard debris containers. Tree-of-heaven plants that have gone to seed should be kept on-site to minimize the spread of the seeds, or bagged before disposal. Larger trees should be chipped or left on-site following removal, when possible. In some areas plant debris can be burned on-site with appropriate safety measures and permits. You should check with your local Fire District or the Oregon Department of Forestry for rules and recommendations.
Diligence is the most important aspect of controlling tree-of-heaven. Removal of new tree-of-heaven plants and monitoring and retreatment of suckering roots may occur years following treatment. So follow-up is required. Work with neighbors to target nearby seeding trees.
It is National Pollinator Week! June 21-27, 2021 has been designated as National Pollinator Week in Oregon and across the country! Join the WeedWise program and other organizations across the country in celebrating our native pollinators. Summer is here and the weeds and wildflowers are blooming all around us. This burst of summer color also […]
It is National Pollinator Week! Join all of us here at the WeedWise program in celebrating our native pollinators. June 22-28, 2019 has been designated as National Pollinator Week and there are activities going on here in Oregon and across the country! Summer is here and the weeds and wildflowers are blooming all around us. […]
It is National Pollinator Week! Join all of us here at the WeedWise program in celebrating our native pollinators. June 17-23, 2019 has been designated as National Pollinator Week and there are activities going on here in Oregon and across the country! Summer is here and the weeds and wildflowers are blooming all around us. […]
A New WeedWise Publication The WeedWise Program is pleased to announce a new publication entitled, Woody Weeds of Clackamas County. This resource guide is intended for use by local landowners and land managers to help them identify and manage woody weeds and naturalizing plants on their property. The Woody Weeds of Clackamas County covers a […]
It is National Pollinator Week! Join all of us here at the WeedWise program in celebrating our native pollinators. June 18-24, 2018 has been designated as National pollinator Week and there are activities going on here in Oregon and across the country! Summer is here and the weeds and wildflowers are blooming all around us. […]
Summer is here and the weeds and wildflowers are blooming all around us. With the burst of summer color, come the many bees, flies, beetles, moths, and butterflies that serve to pollinate these plants. Pollinators are vitally important to the health of our natural areas and local economies. Invasive weeds can play an important role […]
Garlic mustard, Jack-by-the-hedge
Alliaria petiolata (syns. Alliaria alliaria)
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.
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.
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.
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.
This plant has roots that typically feature an S-shaped hook or bend just below the soil line on its single taproot.
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.
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.
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.
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.
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:
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.
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.
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.
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.
Product Names: Accord, Aquamaster, Rodeo, Roundup, and various others
Rate:
Broadcast: 2 – 4 pt product per acre (1.1 to 2.25 lb ae/acre)
Spot treat: use 1% to 3% v/v solution
Time: Postemergence to rosettes in late Fall or early Spring when plants are in the rosette stage.
Comments: Re-treatment may be required to achieve effective control. Glyphosate is not selective and will harm grasses. Use care when working around desirable plants to avoid damage. Mature plants can be controlled with glyphosate with some caveats. Mature plants often die very slowly when applied with Glyphosate and may not halt seed production.
Product Names: Garlon 4 (triclopyr ester), Garlon 3A, Element 3A (triclopyr amine)
Rate:
Broadcast: Triclopyr ester- 8 oz. product per acre
Spot treat: Triclopyr ester use 1.25% to 2.5% v/v solution, Triclopyr amine use 2% v/v solution
Time: Triclopyr provides good control when applied to rosettes through until the mature, flowering stage.
Comments: Triclopyr is selective and will harm desirable broadleaf plants, trees, and shrubs. Use care when working around desirable plants to avoid damage. Leaves should be sprayed until wet but not dripping to achieve good control. Triclopyr ester formulations may volatilize under warm temperatures.
Product Names: various
Rate:
Broadcast: 1 pint product per acre
Spot treat: 1% v/v solution
Time: 2,4-D provides some control when applied to rapidly growing plants before flowering stage.
Comments: 2,4-D can be applied alone or mixed with dicamba. Some reports have shown limited success when treating with 2,4-D.
Product Names: Plateau
Rate: 4 to 6 oz of product per acre
Time: Apply post emergence in fall or early spring.
Comments: Use with a methylated seed oil to improve uptake
Product Names: Escort
Rate: 0.5 to 1 oz of product per acre
Time: Apply post emergence in fall or early spring.
Comments: Use a non-ionic surfactant to improve uptake
Product Names: Oust
Rate: 0.5 oz of product per acre
Time: Apply post emergence in fall or early spring.
Comments: Use a non-ionic surfactant to improve uptake
Product Names: Outrider
Rate: 2 oz of product per acre
Time: Apply post emergence in fall or early spring.
Comments: Use a non-ionic surfactant to improve uptake
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.
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.
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.
Blessed milkthistle, Milk thistle, Marian thistle, Mary thistle, Saint Mary’s thistle, Mediterranean milk thistle, Variegated thistle
Silybum marianum. (Syn. Carduus marianus)
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 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.
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.
Dark brown, relatively heavy hairless achenes, about 1/2 by 1/4 inch, form in autumn.
Plants grow from long white taproots.
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.
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.
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.
Blessed milkthistle is relatively rare in Clackamas County, with populations associated with disturbed and unmanaged sites. Milkthistle is occasionally cultivated as an herbal supplement.
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:
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.
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.
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.
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.
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:
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.
Product Names: Many products
Rate: 3-4 pt product/acre (1.43 to 1.9 lb a.e./acre)
Time: Apply post emergence in spring or fall to young, growing plants.
Comments: 2,4-D is a broadleaf-selective herbicide without residual soil activity. Treat rosettes in the fall. Use spring treatments prior to flower stalk elongation. Treat annually for several years to control seedlings.
Product Names: Milestone
Rate: 3-5 oz product/acre (0.75 to 1.25 oz a.e./acre)
Time: Apply post emergence in spring or to early summer to rosettes and bolting plants. Apply in fall to seedlings and rosettes.
Comments: Aminopyralid is a broadleaf-selective herbicide with moderate soil residual activity. A non-ionic surfactant can enhance control under adverse environmental conditions.
Product Names: Transline
Rate: 0.25-1 pt product/acre. (1.5-6 oz a.e/acre) Spot treatment: 1-2% v/v solution
Time: Apply post emergence from the seedling to bud stage, when plants are rapidly growing
Comments: Generally safe for grass but will harm members of Asteraceae and Fabaceae
Product Names: Curtail
Rate: 1-5 qt product/acre.
Time: Apply post emergence to basal rosettes from spring until bud stage.
Comments: This is a non-selective product and neither compound has soil activity. Replant sprayed area to prevent re-establishment of milk thistle.
Product Names: Banvel, Clarity
Rate: 1-2 pt product/acre (0.5-1 lb a.e./acre).
Time: Apply post emergence to basal rosettes from spring until bud stage.
Comments: This is a non-selective product and neither compound has soil activity. Replant sprayed area to prevent re-establishment of milk thistle.
Product Names: Campaign
Rate: Broadcast foliar treatment: 1-2 pt product/acre. Spot treatment: 1-2% v/v solution
Time: Apply post emergence in spring to rosettes, or in fall before a freeze.
Comments: This is a non-selective product and neither compound has soil activity. Replant sprayed area to prevent re-establishment of milk thistle.
Product Names: Telar
Rate:1 oz product/acre (0.75 oz ai/acre)
Time: Apply post emergence, to rapidly growing plants
Comments: Chlorsulfuron is primarily active against broad-leaf plants and generally will not harm grasses. It has long soil activity. Do not apply to dry, powdery, or sandy soils unless rain is expected.
Product Names: Escort
Rate:1 oz product/acre (0.6 oz ai/acre)
Time: Apply post emergence, to rapidly growing plants
Comments: Metsulfuron is primarily active against broadleaf plants and generally will not harm grasses. It has some soil activity. Use a non-ionic or silicone-based surfactant to increase effectiveness.
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.
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.
Sites should be monitored for several years after the removal of mature plants. Viable seeds can last at least 9 years in the soil.
