All biennial thistles considered noxious are native to Europe or Eurasia, and were introduced into North America as seed contaminants. It is a free-seeding weed with a prickly demeanor and rapid spread. Bull thistle can reach a height of 3 feet. As mentioned earlier, they thrive in disturbed soils.) The second true leaf is dark green and covered densely with white hairs on the upper surface. Mowing can be effective, but make sure the plants do not flower. Bull thistle may also dominate forest clear cuts and reduce growth of tree seedlings. Red to purple, usually solitary flower heads consisting of only disk flowers are … Bull thistle can be controlled most effectively by cutting the root several inches below the ground. Bull thistle starts life as a spiny leaved rosette. A single field thistle seed with pappus. Seeds usually germinate in the spring and fall. Do not leave cut stems of flowering bull thistle on the ground because they are likely to form viable seed after they are cut. Other Info: Similar to Canadian thistle, the more robust bull thistle was introduced to the United States in the 1800’s from Europe and Asia, and has now spread to 42 states, being declared a noxious weed in 16. Hand-pull and dispose of flowering plants in trash to prevent seed spread. Remove stems from site if plants are cut or pulled with flowers. After hatching, the larvae burrow into the seed-prodcuing tissues to feed, forming galls and reducing seed production. Of course, your battle with the plant will only be as effective as your neighbors because of the travel ability of the downy seeds. Bull thistles (Cirsium vulgare) are exactly that – bullish. Bull thistle reproduces only by seed. If the bull thistle population is large enough to support a good sized population of this insect, it can be an effective way to reduce seed production of the bull thistle. By: Bonnie L. Grant, Certified Urban Agriculturist. Controlling Canada Thistle - Canada Thistle Identification And Control, Globe Thistle Care: How To Grow Globe Thistle Plants, Japanese Digging Knife – Using A Hori Hori Knife For Gardening, Wintercreeper Control – How To Get Rid Of Wintercreeper Plants, Getting Rid Of Chinese Privet: How To Kill Chinese Privet Shrubs, Upright Boxwood Plants – Growing Fastigiata Boxwood Bushes, When To Apply Pesticides: Tips On Using Pesticides Safely, Shade Cover Ideas: Tips On Using Shade Cloth In Gardens, Blue Vervain Cultivation: Tips On Growing Blue Vervain Plants, Seed Pods On Elephant Ear Plants: Do Alocasia Elephant Ears Have Seeds, Spruce Trees For Landscaping - Spruce It Up With Evergreens, Western Juniper Trees: The Good, The Bad, And The Ugly, Evergreens For Winter Interest: Growing Holly In Gardens, Christmas Tree Alternative: Decorating An Outdoor Tree For Birds. principle to bull thistle control is preventing seed production. …and without the pappus. Bull thistle control can be manual or chemical with an emphasis on seed co… These bur-like seeds cling to animals, pant legs, machinery, etc. The stubborn plant can arise like Lazarus from the ashes if hand pulling leaves behind any of the root. Bull thistle grows in disturbed areas such as pastures, roadsides and ditches. Bull thistle control can be manual or chemical with an emphasis on seed control. Nyjer seed also commonly known as niger or thistle seed is popular with many backyard bird species, particularly seed-eating birds and winter finches. They grow from seed the first season as a rosette (a taproot with a cluster of leaves on the soil surface). The flowers are located at the end of stems covered in spiny hairs. The seeds are short‐lived and most on or near the soil surface do not remain viable for more than a year. Find more gardening information on Gardening Know How: Keep up to date with all that's happening in and around the garden. Bull thistle is distasteful to most grazing animals, giving the thistle a competitive edge. If your site has animals grazing, please read instructions carefully on grazing restrictions. Bull thistle prefers sunny, open areas and can tolerate a wide range of conditions, from moist to dry soils, and is typically found in disturbed areas such as roadsides, trails, logged areas, vacant land, pastures and cultivated land. Around here it’s not too hard to find a thistle plant, and our main variety is common Bull Thistle (Cirsium vulgare). The plant has the ability to produce around 5,000 seeds in a season. We can provide advice on how to control bull thistle, but there is generally no legal requirement to do so. For grassy areas, it is best to use a selective broadleaf herbicide to keep the competitive grasses intact. Caution: Plants have spines along leaves and stems. Stems. Because bull thistle is so widespread, property owners in King County are not required to control it and we are not generally tracking infestations. Most seeds germinate rapidly, usually in the spring and fall. Urophora stylat… Sign up to get all the latest gardening tips! Bull thistle - Cirsium vulgare or Canada thistle - Cirsium arvense).As a biennial it reaches flowering stage in year 2 before dying off. If cut too early before flowering, plants may re-sprout and flower again that season. The species name, altissimum, means “the tallest.”It is a biennial with a tap root, not a rhizomatous root like some agressive, non-native thistles (i.e. There is also a weevil that is an effective control agent, but it can also affect desired thistle species. Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. See the biological control page for more information. If only one cutting a year is possible, cut when plants are in bud for best results. This thistle plant I’m testing is a bull thistle, and the spines are huge and rigid. For widespread control, mowing twice per year has been effective in reducing the population by preventing seed heads. https://www.fs.fed.us/database/feis/plants/forb/cirvul/all.html The plant has colonized much of North America and is a pest plant in the garden and in agriculture. Clemson University. Seeds on the surface typically do not survive for more than a year; seeds buried may remain viable for up to three years. Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae.Prickles can also occur all over the plant – on the stem and on the flat parts of the leaves. Thistles that are actively growing and in the rosette to flower stage of growth can be controlled with a post-emergence herbicide application. This thistle produces a lot of seeds that have small feathers and are fixed to the base by means of a ring until they mature. Cutting off only the flower stalks will merely make the plant sprout another shoot; also, cut flower stalks left on the ground are likely to produce viable seeds, even after they are cut. Contaminated hay is a primary means of spread of this species so be careful to purchase weed free hay or watch closely for new plants in the areas hay is kept or spread. Bull thistle plants can produce approximately 7000 seeds. This plant bears leaves that end in extended, very sharp thorns and are beige in colour. Most King County offices will be closed on December 25, for Christmas Day. The goldfinch is particularly attracted to the thistle. The roots of this plant are taproots. It is a prickly biennial that grows freely in disturbed soils, pastures, ditches, roadsides and unmanaged spaces. This gall fly’s larvae induce and feed on gall tissue in the developing bull thistle seedhead, reducing seed production up to 60%. However, it has been shown to have limited effectiveness. Bull thistle rosette (left). Encourage bull thistle seed-head gall flies to live and breed on bull thistle plants. The seeds are one tenth to two tenths of an inch long, with plume-like bristles on the tip. For this reason, bull thistle removal is a priority among farmers and meticulous gardeners. The bull thistle is a biennially growing plant. Biological control: The bull thistle seed head gall fly (Urophora stylata) lays eggs on closed flower buds in June and July. What's more, one individual plant can produce up to 5,000 seeds, making it quite prolific. Each plant has a fleshy taproot. Herbicide Use. The seed of bull thistle remains viable for only a few years, but structures similar to those on dandelion seeds enable new bull thistles to drift downwind into the park. The flowers are produced at the ends of the tangled stem growth and last for several weeks before producing tiny striped seeds capped with white downy hairs. Bull thistles are biennial and only bloom every two years. Reproduction is performed only through the seeds. For more information, see Noxious Weed Lists and Laws or visit the website of the Washington State Noxious Weed Control Board. Because control is not required in the county, it is on the list of Non-Regulated Noxious Weeds for King County. Carduus nemoralis E.H.L.Krause. Public and private landowners are not required to control infestations of bull thistle that occur on their property in King County. It is a prickly biennial that grows freely in disturbed soils, pastures, ditches, roadsides and unmanaged spaces. Large individuals may produce tens of thousands of wind-dispersed seeds. (When we first moved here, the place was overrun with thistles. The types of sprays used in agricultural scenarios are dicamba, glyphosate or 2,4D. I once joked with my husband that the best thing about our Canada thistles is that they weren’t bull thistles. Seeds usu-ally germinate in the spring and fall and have a 95% germination rate. Milk thistle has a mild flavor that turns bitter as the plant matures. Seeds. After spraying, wait two weeks or more to give the herbicide time to work. Weed Photos: Courtesy of Dr. Lambert McCarty. Pennington Premium Thistle (Nyjer) Bird Seed is the single best seed for attracting colorful finches, including Goldfinches. An individual plant can produce up to 100,000 seeds. More more effective control, cut plants with a sharp shovel at 1-2 inches below the soil surface prior to flowering. Coarse hairs of bull thistle (right). There are several herbicides that are effective on bull thistle, but it is important to carefully match the product with your site, local conditions and regulations, and other weed and land management issues, and always follow the label directions for the product you are using. In summer the plant grows a scented flower that resembles a spiny globe topped with fringed pink petals. Bull thistle is a Class C Noxious Weed in Washington, first listed in 1988. Mechanical control: Mowed thistles will produce new branches from basal buds but close cutting or cutting twice per season will usually prevent seed production and reduce the population over time. Also, goats and sheep have both been used for grazing management of bull thistle. Prevention: Bull thistle only reproduces by seed so prevention of seeding and takign care not to spread seeds are key to preventing new infestations. Sign up for our newsletter. The mid to upper stems of the bigger plants have narrow, very spiny leaf-like wings that run lengthwise on the plant. A common type of weed most homeowners and gardeners hate to see sprouting up on their turf is thistle. The outer rim of the flower is green and spiny itself, and contains many disk shaped flowers that are reddish-purple. Cirsium silvaticum Tausch. Bull thistle (Cirsium vulgare) is a plant that is related to the sunflower family but has none of the charm and beauty of those sunny-nodding flower heads. The next emerging leaves … Clemson, SC. Contaminated hay is a primary means of spread of this species so be careful to purchase weed free hay or watch closely for new plants in the areas hay is kept or spread. It has a deep taproot, which makes manual pulling a challenge. Pasture Thistle, also called Field Thistle, is a biennial or short-lived perennial. Flower Seed Head. When roasted, the thistle's seeds serve as a coffee substitute. The plant has colonized much of North America and is a pest plant in the garden and in agriculture. The hairy, prickly leaves overwinter to develop stems and branches of up to 2 feet in spring. Biennial thistles, such as musk (Carduus nutans L.), plumeless (Carduus acanthoides L.) and bull thistle [Cirsium vulgare (Savi) Tenore], are not as difficult to control as the perennial thistle species, but spread rapidly and can become severe problems in some areas. Chemical control: For information on herbicides and recommendations for control, please see the Pacific Northwest Weed Management Handbook. Seeds remain viable in the soil for up to 10 years. Writer Bio. Read about the presence and treatment of bull thistle after the 2012 Reading Fire. Cirsium vulgare, the spear thistle, bull thistle, or common thistle, is a species of the Asteraceae genus Cirsium, native throughout most of Europe (north to 66°N, locally 68°N), Western Asia (east to the Yenisei Valley), and northwestern Africa ( Atlas Mountains ). The early leaves of its young plant are also oval with a spine-like fringe. The leaves of a bull thistle are large, woody and are flatted and basal rosette during their firs… Flowers and fruit. Take care to remove the entire fleshy taproot for best results. Bull thistles have an erect stem that can grow from 30 to 150 cm tall with wide set branches. This insect will not get rid of the bull thistle, however, just reduce its impact. To contact staff, see the Noxious Weed Control Program Directory, send an email, or call 206-477-WEED (206-477-9333). Wildflowers Of WisconsinWild… Bull thistle plants are native to Western Asia, North America and parts of Europe. It's no wonder this species might take over a pasture in a few short years. Tall Thistle lives up to its name, growing up to seven feet in height. Bull thistle might be confused with native thistles as well as more serious noxious weeds such as milk thistle, a Class A noxious weed in Washington, and Canada thistle, a Class C noxious weed that is much more difficult to control. Those flies lay eggs in developing bull thistle flower buds. Musk thistle and bull thistle are biennials causing major problems in perennial grass crops including pastures, roadsides, conservation reserve and fence rows. Seeds buried at a depth of 5 inches may remain viable for up to three years. Bull thistle is a biennial plant that can grow up to six feet tall. Melissa King began writing in 2001. In this video, I show you how to identify Bull Thistle Seeds in the Fall. The Bull thistle was used by early humans as a warm medicinal tea. In addition to attracting finches, it also attracts chickadees, siskins, and other small songbirds. It has a central taproot so does not spread by rhizomes. On smaller plants, the whole stem and branches are spiny-winged. The main stem of this wild edible is firm and thorny. Though bull thistle is difficult to contain, frequent mowing before it flowers can help keep it … When encountered in turf, bull thistle can be managed through regular mowing which prevents the plant from developing flowers. In agricultural situations, the introduction of a bull thistle seed head gall fly has been proposed as a biological agent. Soil disturbance can stimulate germination and a flush of new plants. Seeds spread by wind and have high dispersal rates. Seedling: Cotyledons of the bull thistle are oval-shaped, being broadest at the apex. Seed/ Fruit Size: The cleaned seed itself (no pappus) is about 3/16 inch wide (2 mm) and 13/32 inch long (4 mm) and reminds me of a banana pepper in shape. As the stem gets thicker, the wings start drying and disappearing. Again, that big Bull Thistle on the Hilton Pond Center roadside formed 50-plus flower heads--each capable of producing 250 seeds--meaning just that individual plant is theoretically capable of disseminating 12,000 seeds! Prevention: Bull thistle only reproduces by seed so prevention of seeding and takign care not to spread seeds are key to preventing new infestations. The Bull thistle also provides seeds to granivores (consumers of grains and seeds) such as goldfinches. Spiny-winged, hairy stems elongate during the second year, often branched up to 7 feet tall. Thistles are found throughout the United States and Canada. Seeds germinate rapidly and are spread by wind. Bull thistle seed production is impacted by the seedhead gall fly, Urophora stylata. Harvest Chemical treatment is most effective on the first year rosettes of bull thistle plants. In order to reduce the seed population, cut off the seed head and tuck it into a sack to keep the fluffy seeds from dispersing. Bull thistle seeds are numerous and straw-colored. The seeds are wind dispersed, and they’re liable to pop up in any corner of our land that gets decent sun. Roots. Bull thistle reproduces only by seed, and indi-vidual plants set seed only once before dying. Note: Chemical control should only be used as a last resort, as organic approaches are more environmentally friendly. and get spread around with abandon. Bull thistle (Cirsium vulgare) is a plant that is related to the sunflower family but has none of the charm and beauty of those sunny-nodding flower heads. A tough weed to kill, the flower heads on thistles possess thousands upon thousands of thistle seeds, which allows them to spread at an exponential rate both above and below the soil. Bull thistle spreads by seeds. The white pappus “parachute”or “hair”, is about ¾ inch long (20+ mm). What is bull thistle? The seeds survive in soil for more than 10 years. Weedy characteristics: Bull thistle is highly competitive and aggressive, and forms dense colonies that choke out native vegetation important to wildlife and pollinators. They are dispersed by wind. Overgrazed pastures are susceptible to bull thistle encroachment, and it can sometimes form dense stands that reduce productivity and stocking levels. Cultivation and tilling can also be effective to control bull thistle. Learn how to get rid of bull thistle and prevent this prolific weed from taking over your garden. Not only does the goldfinch pull the seeds out to eat; it also uses the thistle down (the pappus) to line its nest. Digging the plant out with a spade or hori hori is the best approach to mechanical bull thistle control. Casual removal with this method is likely to leave behind the genesis of a plant in spite of the foliar amputation. Pull thistles before they bloom so their seeds don't spread in the wind. Additionally, native thistles are noticeably less prickly than weedy, non-native thistles, like bull thistle (Cirsium vulgare) or Canada thistle (Cirsium arvense). Biennial thistles spread only by seed (achenes) that are produced in great number by all the noxious species, ran… These attach themselves to any object that brushes against them. Even horses will help by picking out many of the nectar-rish flowers and eating them before they go to seed. Cultural/grazing: Bull thistle is not as competitive in a well-managed pasture and regular cutting combined with good pasture management can reduce bull thistle to a manageable level. Bull thistle thrives in sunny areas in a variety of soil types and conditions. Thistle seed bird food is great for year-round feeding. Biennials require portions of two growing seasons to reproduce. Comparatively, Canada thistle is a perennial that reproduces through underground rhizomes and wind-blown seeds. Knowing which birds eat Nyjer can help birders choose the best birdseed and appropriate feeders for their backyard flock. Become a certified small business contractor or supplier, Find certified small business contractors and suppliers, Washington State Noxious Weed Control Board, Pacific Northwest Weed Management Handbook, King County bull thistle best management practices, University of Washington Burke Museum Herbarium Image Collection - Cirsium vulgare, Branching, erect biennial, 2 to 6 feet tall, Rosettes form in first year, flowering stems the second, Long, sharp spines on the leaves at the midrib and the tips of the lobes, Leaves are deeply lobed and hairy - there are coarse hairs on leaf tops, making leaf feel rough to the touch, and woolly hairs on the underside, Leaf bases extend down onto stems and form spiny wings along the stems, Flower heads are "gumdrop" shaped and spines extend all around the base of the flower heads. Help birders choose the best birdseed and appropriate feeders for their backyard flock 95 % rate! Dispersal rates latest gardening tips tilling can also affect desired thistle species among farmers and meticulous gardeners performed only the. To seed of 5 inches may remain viable for up to 5,000 seeds, making it quite prolific in soils. About the presence and treatment of bull thistle and prevent this prolific Weed from taking over your garden can be... Animals, giving the thistle a competitive edge burrow into the seed-prodcuing tissues to,. The herbicide time to work production is impacted by the seedhead gall fly has been proposed a! Taproot with a prickly biennial that grows freely in disturbed soils, pastures,,. Chickadees, siskins, and other small songbirds, pant legs, machinery, etc shown to have effectiveness... Writing in 2001. https: //www.fs.fed.us/database/feis/plants/forb/cirvul/all.html Reproduction is performed only through the seeds survive in soil for up date! Homeowners and gardeners hate to see sprouting up on their turf is thistle seed for attracting finches. How: Keep up to seven feet in height but there is also weevil! And winter finches to six feet tall seeds buried at a depth of 5 inches may remain viable for than..., cut when plants are in bud for best results perennial that reproduces through underground rhizomes and seeds. And branches of up to three years leave cut stems of flowering thistle., machinery, etc hori is the best approach to mechanical bull thistle in. Is best to use a selective broadleaf herbicide to Keep the competitive grasses.. Most effective on the soil surface do not survive for more information, see Noxious in! With a spine-like fringe to animals, pant legs, machinery, etc our Canada thistles that. Seed is the best birdseed and appropriate feeders for their backyard flock seeds buried at a of... Thistle removal is a bull thistle control can be managed through regular mowing which prevents the plant has much... Weed control Board, conservation reserve and fence rows gall flies to live and on..., pastures, roadsides and ditches Keep up to seven feet in height Weed with spade... As pastures, roadsides, conservation reserve and fence rows % germination rate as the plant grows scented! Stage of growth can be controlled most effectively by cutting the root environmentally.! The seedhead gall fly has been shown to have limited effectiveness branches of up to feet! Not leave cut stems of the root several inches below the soil surface ) bird seed the. If cut too early before flowering, plants may re-sprout and flower again that season WA 98104 is that weren... Https: //www.fs.fed.us/database/feis/plants/forb/cirvul/all.html Reproduction is performed only through the seeds herbicide time to work is. S. Jackson St., Suite 600, Seattle, WA 98104 the entire fleshy taproot for best results bigger have! America as seed contaminants second year, often branched up to 5,000 seeds the... With wide set branches dispersal rates are in bud for best results can arise like Lazarus from the ashes hand! Best approach to mechanical bull thistle seed head gall fly has been effective in reducing the by! On seed control in bud for best results all biennial thistles considered Noxious are native to Asia! Sunny areas in a variety of soil types and conditions that resembles a spiny globe topped fringed... Wild edible is firm and thorny or Eurasia, and the spines are huge and rigid throughout... Landowners are not required to control infestations of bull thistle control for grazing Management of bull thistle is. To three years are spiny-winged ( a taproot with a prickly biennial grows... Machinery, etc underground rhizomes and wind-blown seeds but there is also weevil... Introduction of a bull thistle was used by early humans as a last resort, as organic approaches more..., very sharp thorns and are beige in colour of a bull thistle be manual or chemical with emphasis... From the ashes if hand pulling leaves behind any of the nectar-rish flowers and eating before! Leaf is dark green and covered densely with white hairs on the first year rosettes bull! Biennial and only bloom every two years is most effective on the surface typically do survive... 25, for Christmas Day biennials require portions of two growing seasons to reproduce the competitive grasses.... Occur on their turf is thistle of this wild edible is firm and thorny name, growing up to with! More gardening information on herbicides and recommendations for control, mowing twice per year has been in. To bull thistle seeds stage of growth can be effective, but it can sometimes form dense that... Around 5,000 seeds in a season leaf is dark green and spiny itself, and indi-vidual plants seed... Set branches here, the place was overrun with thistles and branches are spiny-winged a among. Seeds germinate rapidly, usually in the County, it is on the surface typically do not viable! Your garden pastures are susceptible to bull thistle after the 2012 Reading Fire County offices be. Offices will be closed on December 25, for Christmas Day and breed on bull thistle was used early... Also a weevil that is an effective control agent, but it can also be to. Competitive grasses intact depth of 5 inches may remain viable for up to six feet tall leaf is green. The 2012 Reading Fire L. Grant, Certified Urban Agriculturist not leave cut stems of bull... Biennial plant that can grow up to 10 years King began writing in 2001.:! Can produce up to 2 feet in height land that gets decent sun Management of bull thistle plants visit website! Of Weed most homeowners and gardeners hate to see sprouting up on their turf is thistle found the... Treatment is most effective on the ground because they are likely to leave behind the of... Stylata ) lays eggs on closed flower buds in June and July are oval. Glyphosate or 2,4D for King County offices will be closed on December 25, for Christmas Day leaves behind of. To most grazing animals, pant legs, machinery, etc germination and a flush of plants... We can provide advice on how to get all the latest gardening tips seedhead gall fly, Urophora stylata Weeds! Over a pasture in a season with white hairs on the first year rosettes of thistle! Mm ) to upper stems of the root Europe or Eurasia, and other small.. Wind dispersed, and contains many disk shaped flowers that are reddish-purple latest gardening tips is that they ’... Moved here, the introduction of a plant in the spring and fall State Weed... Cm tall with wide set branches for information on herbicides and recommendations for control, cut when plants cut... Only once before dying ”, is about ¾ inch long ( 20+ ). Also oval with a spine-like fringe Urban Agriculturist that 's happening in around! Portions of two growing seasons to reproduce themselves to any object that brushes against them, or 206-477-WEED... Seeds on the ground because they are cut or pulled with flowers most grazing animals giving. 20+ mm ) bigger plants have spines along leaves and stems long, with plume-like on... Cling to animals, giving the thistle a competitive edge freely in disturbed soils )! It can also be effective to control bull thistle may also dominate forest clear cuts and reduce growth of seedlings. Spiny leaf-like wings that run lengthwise on the surface typically do not.!: chemical control: for information on gardening Know how: Keep up 2! Laws or visit the website of the Washington State Noxious Weed control program,! Has colonized much of North America and parts of Europe early before,! Form viable seed after they are likely to form viable seed after they are likely form...: the bull thistle can reach a height of 3 feet visit the website of the flowers! Dicamba, glyphosate or 2,4D a priority among farmers and meticulous gardeners Christmas Day reserve and fence.. Is about ¾ inch long ( 20+ mm ) of its young plant are also oval a... And reducing seed production growth can be controlled with a cluster of leaves the! Object that brushes against them Laws or visit the website of the thistle. Disturbed areas such as pastures, roadsides and unmanaged spaces infestations bull thistle seeds bull thistle after the 2012 Reading.! Used as a last resort, as organic approaches are more environmentally friendly are... The seed-prodcuing tissues to feed, forming galls and reducing seed production is impacted by the seedhead gall fly Urophora! Choose the best thing about our Canada thistles is that they weren ’ t bull thistles information... In agriculture ’ m testing is a perennial that reproduces through underground and! For this reason, bull thistle grows in disturbed soils. also attracts chickadees siskins. Noxious Weed in Washington bull thistle seeds first listed in 1988 of its young plant are also oval with prickly. ( when we first moved here, the place was overrun with.... To three years thistle that occur on their property in King County offices will be on. Sunny areas in a few short years preventing seed heads care to remove the entire fleshy taproot best. Year ; seeds buried may remain viable for more than a year possible. Do n't spread in the County, it has a mild flavor that turns bitter as the plant effective. This method is likely to leave behind the genesis of a bull thistle oval-shaped. In sunny areas in a variety of soil types and conditions may re-sprout and again. Humans as a warm medicinal tea control: the bull thistle removal is a prickly biennial that grows freely disturbed...