Noxious Weeds
Idaho has 64 different species of weeds which are designated noxious by state law. The spread of these weeds and the damage they do to Idaho agriculture can be lessened through proper identification and handling.
Below are a few of Twin Falls County’s most prevalent noxious weeds, with quick facts and control methods for each.
You can also go to the Idaho State Department of Agriculture’s website for all of the weeds and information, https://invasivespecies.idaho.gov/plants.
Spring Time Weeds
Quick Facts:
- Toxic to livestock, attacking the liver and producing neurological effects. The plant is rarely eaten in the green state; however, animals will eat the dried plant in hay
- Reproduces by seed. The seed is coated with Velcro like hairs that attach to animals and clothing
- A single plant can generate 300 to 600 seeds per plant that can remain viable for up to 4 years
Control:
- Over grazing will prompt this weed to take over and displace desirable and more beneficial grasses and forbs
- Small areas can be eradicated by digging, pulling, or mowing. To break the cycle of the plant, physically remove the plant at flowering or in early seed formation. You can pull or dig these weeds out. be sure to bag and destroy the plant so seeds do not mature after you pull it. Burning is not any effective method of control.
- You want to apply herbicides during the pre-bud stage or in the rosette stage. Pre-bud occurs in the spring to early summer and the rosettes from in late summer and early fall. Products such as those containing 2,4-D or Dicamba (Banvel) have proven effective, however, annual treatments may be necessary to assure the seed bed as been depleted. Adding a surfactant to your herbicide is recommended due to the plant’s hairy leaf surface. Treatments should be applied during the rosette stage through bolt prior to flowering, and late in the fall. Always read and follow the label when using any herbicide
Quick Facts:
- Extremely toxic to anything that consumes it. Hemlock poisoning causes paralysis, convulsions, and eventual death. It is important for growers to notice and remove any hemlock from their hay or pasture fields, including ditch banks, fence rows, and other idle areas.
- Reproduces solely by seed. Seeds germinate in autumn and plants develop rapidly throughout the winter and spring
- Can be distinguished by the purple spots on the stem. It is commonly confused with wild carrot, cow parsnip, and parsley. Human deaths have occurred from harvesting and consuming this plant.
Control:
- To prevent seeds from spreading, it is important to minimize soil disturbance. Eradicate new and or small infestations immediately by hoeing, pulling, or mowing before or at early flower stage. It is important to implement proper seeding, grazing, fertilizations, and irrigation management to promote the growth of desired species
- In cropland, plowing or repeated cultivation will prevent Poison hemlock, establishment. In other areas, repeated mowing can be used to remove bolting plant material, reduce its competitive ability, and prevent seed production.
- Herbicide can be applied any time after the sprouts have emerged. Herbicides such as 2,4-D (amine and ester formulations), MCPA, and Escort are effective. Approved aquatic formulations are available to control plants near water. Treating this weed with herbicide map require repeated applications to deplete the seed bank. The length between applications depends on the herbicide. Always read and follow the label when using any herbicide.
Quick Facts:
- Plants produce 8,400 to 40,000 seeds
- Reduces forage production and virtually prohibits land utilization for livestock. The only animal known to graze this plant is a goat
- Has been credited with helping Scotland fend off Viking invasions. As the Vikings moved into Scotland for a sneak attack, they yelled out in pain when they stumbled through thistle plants
Control:
- Small areas can be eradicated by digging. Plants must be cut off below the soil, leaving no leaves attached. Mowing has limited effect; it usually prevents seed production if done prior to flowering or when plants are just starting to flower. Mowing too early will only delay flowering. If plants are cut too late in the flowering stage, viable seeds can still develop. Because there can be a wide variety in the maturity of plants, a single mowing is not likely to provide satisfactory control
- Establishing and maintaining dense, vigorous, competitive pasture can effectively prevent establishment. Healthy pasture is particularly important in the autumn, when most Scotch thistle seeds germinate
- There are herbicides on the market that, if applied correctly, have proven effective. Non-crop, grass-friendly products like Milestone, Redeem, Transline, Curtail, Escort, and Telar have proven to be the most effective. Late season treatments of Telar may temporarily injure cool season grasses. Other products such as those containing 2,4-D or Dicamba have also been used. Herbicides are best applied when the weed is in the rosette through bolt stage. Always read and follow the label when using any herbicide
Quick facts:
- is a deep-rooted perennial that reproduces by seed and root
- flowers from May through June and begins producing seeds by July
- A single plant can produce between 1,200 to 4,800 seeds that can remain viable in the soil for up to three years
- Can be consumed by sheep when the plant is young
- Cattle that are exposed to this weed will produce tainted milk
- Most livestock tend to avoid this weed while grazing
- 90% of the time, infestations will occur in disturbed areas
- Roadside grading can spread the plant one mile in a single year
Control:
- Digging can provide control of small infestations if the entire root is removed. This should occur within 10 of emergence throughout the growing season
- Hand pulling, in general, is not effective because the root system may not be entirely removed
- Cultivation is the major factor for the spread of the plant because root fragments will be left behind, producing new plants. The only way cultivation can be effective is if it’s repeated frequently throughout the growing season for several years
- Frequent mowing can remove biomass, seed production, and shoots produced. Plants that were moved during flowering produced fewer viable sees than plants that were mowed during bolting
- Herbicides can be used to control this weed, but success can be difficult. Non-crop products like Escort and Telar have proven to be the most effective. Other products such as those containing 2,4-D or Dicamba have also been used. Applications made when the weed is at the bud though flower stage will translocate better to the roots and rhizomes, however, annual treatments may be necessary. Always read and follow the label when using any herbicide.
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- Houndstongue
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- Poison hemlock
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- Scotch thistle
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- White top
Summer and Fall Weeds
Quick Facts:
- Native to the Great Plains region of the U.S.
- Contaminant of bird seed
- Disperses by tumbling in the wind; seeds attach to animals or equipment
- Seed longevity not reported
- Annual with yellow spines and star-shaped hairs; up to 2 feet tall
Control:
- Contact the Twin Falls County Noxious Weed Department for control methods
Quick Facts:
- A creeping perennial that reproduces from seed and vegetative roots
- Can colonize in an area 3 to 6 feet in diameter in one year. Horizontal roots may extend 15 feet or more and vertical roots may grow 6 to 15 feet deep
- Develops seed sparingly, 1,000 to 1,500 seeds per flowering shoot, transported long distances by water, animals, clothing, farm equipment, and vehicles. It is also known to be a common crop seed contaminant. Wind may help disperse the seed, but most often the feathery pappus breaks off, leaving the seed attached to the parent plant
- Seed can remain viable in the soil up to 22 years. Deep burial of seed can prompt seed survival to be even longer
Control:
- Mowing has a tendency to stimulate new shoots to develop from the foot system. If conducted often enough, mowing will prevent seed production however, plants will continue to spread through the soil by root
- Disking will prompt patches to grow larger and spread quickly to non-infested areas. Each dissected root segment will generate new plants
- Non-crop, grass-friendly products like Milestone, Redeem, Curtail, Transline, and Telar have proven to be the most effective. Late season treatments of Telar may temporarily injure cool season grasses. Other products such as those containing 2,4-D or Dicamba have also been used. Applications made when the weed is at the bud through flower stage will translocate better to the roots, however, annual treatments may be necessary. Always read and follow the label when using any herbicide
- Controlling Canada thistle in an irrigated broadleaf crop is difficult. It is best to consult your field advisor to carefully plan control options based on your specific crop rotation schedule
Quick Facts:
- A tough competitor that will rapidly invade and dominate disturbed areas
- Reproduces solely from seed. Each plant can produce up to 18,000 seeds that remain viable and dormant in the soil for several years
- Should not be pulled with bare hands. Plant juices absorbed through the skin can make you sick
- Has little value as feed for livestock; and its thistle like flower heads can damage the mouth and digestive tract of animals that attempt to feed on it
Control:
- It is important to minimize soil disturbance. Small infestations can be hoed, pull (with gloves), or mowed before the weed is in full bloom. If plants are cut too late in the flowering stage, viable seed can still develop
- This weed cannot tolerate cultivation or excessive moisture, so it does not pose a threat to cultivated fields
- Herbicide products such as Milestone, Redeem, Transline, Curtail, and those that contain 2,4-D or Dicamba (Banvel/Vanquish) are effective when applied to the weed in the rosette through bolt stage. Always read and follow the label when using any herbicide
Quick Facts:
- A creeping perennial that reproduces from seed and vegetative roots. This weed has a deep root system that can grow to a depth of 20 feet. Seeds can rain viable in the soil for up to 40 years
- Not generally consumed by livestock and is known to be toxic to pigs
- Can reduce crop yields up to 50% or more and can complicate tillage and harvesting be clogging machinery and entangling plants
Control:
- Hoeing, pulling, or covering is not effective in controlling this weed
- Disking will prompt patches to grow at a faster rate and spread quickly to non-infested areas. Each dissected root segment will generate new plants
- There are herbicides on the market that will inhibit seed production and work to drain root reserves. Products such as Escort, Roundup, Banvel, Clarity, Landmaster, Rifle, and 2,4-D are labeled for use. Effectiveness will depend on the seed bed in soil, time of application, and growth stage. Always read and follow the label when using any herbicide. Check labeling for proper use in crop, non-crop, and turf areas. Products like Escort, Roundup, and Landmaster will harm or kill grasses
- Controlling Field bindweed in an irrigated broadleaf crop is difficult. It is best to consult your field advisor to carefully plan control options based on your specific crop rotation schedule
Quick Facts:
- Flowers emerge in early May to August and may produce 1,200 seeds per head and as many as 120,000 per plant. Seeds may remain viable in the soil for over ten years
- Is usually a biennial although it may germinate and flower in a single year. It typically grows in open disturbed soil or heavily grazed areas
- Generally prefers to grow in pastures because the drainage is good, and livestock will avoid it due to its spiny leaves and stems
Control
- Small areas can be eradicated by digging. Plants must be cut off below the soil, leaving no leaves attached. Mowing usually prevents seed production, if done prior to flowering. When plants are cut or mowed late in the flowering stage, viable seed can still develop. Because there can be a wide variety in the maturity of plants, a single mowing is not likely to proved satisfactory control
- Establishing and maintaining dense, vigorous, competitive pasture can effectively prevent establishment. Healthy pasture is particularly important in the autumn, when most thistle seeds germinate. It is important not to over-graze pastures or dry rangeland areas
- There are herbicides on the market that have proven effective. Non-crop, grass-friendly products like Milestone, Redeem, Transline, Curtail, Escort, and Telar have proven to be the most effective. Late season treatments of Telar may temporarily injure cool season grasses. Other products such as those containing 2,4-D or Dicamba have also been used. Treatments should be applied during the rosette stage through bolt, and late in the fall. Always read and follow the label when using any herbicide
Quick Facts:
- Also known as Pepperwort or Peppergrass
- Can alter ecosystems by acting as a ‘salt pump’ extracting salt ions from deep in the soil and depositing them near the surface, causing a shift in plant composition
- It is adaptable to many environmental factors, and can tolerate a wide range of soil condition
- Perennial herb that can grow up to 6 feet tall
- Long creeping roots can penetrate to a depth of 9 feet
- The plant reproduces vegetative and by seed dispersal allowing it to easily spread via water currents and human/ animal vectors
Control:
- Contact the Twin Falls County Noxious Weed Control office for recommendations and help with infestations
Quick Facts:
- Will produce 200 to 5,000 seeds during one growing season. Seeds may remain viable in the soil for up to 5 years
- Infested areas should not be grazed by livestock. The sharp spines of the seed burr can injure the mouth and digestive tract of animals. It is particularly toxic to sheep, causing sensitivity to light resulting in skin lesions and swelling of ears and lips. Severe effects include blindness, necrosis of skin, loss of lips and ears, and death in young animals
Control:
- Long-term control can be achieved by reducing the amount of seed in the soil. This is best accomplished by removing plnats before they produce seed (i.e., before or at flowering) and continuing to do so over several years. Burrs that have dropped after removing the plant may be collected and removed by sweeping or raking the ground.
- Shallow tilling (about 1 inch deep) can be effective in large areas. Hand removal, hoeing, or cultivation should be initiated prior to flowering and seed production. Mowing is not effective since the plant grows low to the ground
- Aeration of compacted sites and planting competitive desirable plants can reduce the impact of this weed by making the area more favorable for the growth of the desired plants
- There are herbicides on the market that, if applied correctly, have proven effective. An early spring treatment of Telar as a pre-emergent application has proven to give season long control. Other products such as those containing 2,4-D or Dicamba have also been used are best applied after germination to flower stage. Always read and follow the label when using any herbicide
Quick Facts:
- Is an invasive plant that rapidly reproduces to form dense monocultures, inhibiting the growth of nearby plants
- It decreases biodiversity, reduces hay and forage values, and disrupts recreation activities
- Sharp spines deter grazing animals and if ingested is toxic to horses causing chewing disease
- Can be an annual or perennial that can grow 2-3 feet tall
- Rosettes have spines in the center
- Leaves are 4-8 inches long, hairy, with lobed margins
- Flowers are purple to pink with spine-like bracts over 1 inch long
- Seeds do not have plumes and are the distinguishing feature between it and Iberian starthistle
Control:
- Contact the Twin Falls County Noxious Weed department immediately if found
- Make sure to remove and properly dispose of all seed and plant materials on vehicles, clothing, shoes, and pets before you exit or enter outdoor recreational sites
Quick Facts:
- An aggressive plant that favors coarse-textured, well-drained soils. It competes well for water and nitrogen
- Has a slender, simple taproot that can reach over 6.5 feet deep and can branch horizontally
- Cereal grain and potato production are at risk. Impacts include reduced yield due to competition and harvest difficulties with combine harvesters from latex sap that is exuded from the plant
- Can produce 1,500 flower heads and is capable of producing up to 20,000 seeds per plant. This perennial plant generally blooms July through September
Control:
- Hand-pull small infestations when soil is wet. It may be necessary to pull plants 2 to 3 times a year for several years to keep new plant from emerging. Pulled plants should be destroyed by burning
- Frequent mowing can remove biomass, seed productions, and shoots produced
- Herbicides can be used to control this weed. Labeled products include Milestone, Transline, Stinger, 2,4-D or MCPA, and Tordon. Herbicide applications should be made when the weed is young through the bolt stage. Always read and follower the label when using any herbicide
Quick Facts:
- A creeping perennial that reproduces from seed and vegetative roots. It produces 50 to 500 seeds per shoot with a root growth of 12 square yards in two growing seasons
- It produces biochemicals that inhibit the growth of other plants
- It is toxic to horses and not desired forage for cattle. Eliminating knapweed will allow grasses to re-establish, however, planting a dry land grass in non-irrigated areas or pasture mix to irrigated areas not previously seeded will provide optimum benefit and use for grazing livestock
Control:
- Frequent mowing will place stress on the plant, however is not considered effective as the root of this plant will continue to thrive
- Disking knapweed will prompt patches to grow at a faster rate and spread quickly to non-infested areas
- There are herbicides on the market that, if applied correctly, have proven effective. Older, more established stands should be monitored annually to assure seed bed has diminished and/or disturbance has not prompted re-emergence. Products such as Milestone, Redeem, Transline, Curtail, and Telar are effective when applied at the bud to bloom stage and in the fall. Always read and follow the label when using any herbicide
- Controlling Russian knapweed in an irrigated broadleaf crop is difficult. It is best to consult your field advisor to carefully plan control options based on your specific crop rotation schedule
Quick Facts:
- Native to Europe
- Potential allelopathic effects; highly competitive
- Produces up to 25,000 seeds per plant
- Seeds disperse less than 9 feet or long distances if ingested by or attached to animals
- Seeds remain viable for more than 8 years
- Biennial or short-lived perennial with branched stems; up to 3 feet tall
Control:
- Contact the Twin Falls County Noxious Weed Control office for Control methods
Quick Facts:
- Native to eastern Mediterranean area
- Dispersal not reported; likely similar to spotted knapweed
- Seed longevity not reported
- Perennial; 1 1/2 – 3 feet tall with woody base
Control:
- Contact the Twin Falls County Noxious Weed Department for Control methods
Quick Facts:
- Native to the Mediterranean region
- Often grown as an ornamental
- Reproduces from rhizomes and seed
- Likely able to move along streams more than 100 yards per year
- Seeds have increased germination after fire
- Perennial; mature plant less than 4 feet tall; can survive drought periods of longer than 3 months
Control:
- Contact the Twin Falls County Noxious Weed Control department for control methods
Quick Facts:
- Native to Europe
- All parts of the plant are poisonous, but especially the root
- Disperses long distances by birds; check areas where birds perch
- Longevity not reported
- Climbing perennial vine up to 50 feet in length with tendrils
Control:
- Contacts the Twin Falls County Noxious Weed Departments for control methods
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- Buffalobur
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- Canada thistle
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- Diffuse knapweed
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- Field bindweed
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- Musk thistle
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- Perennial pepperweed
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- Puncturevine
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- Purple starthistle
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- Rush skeletonweed
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- Russian knapweed
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- Spotted knapweed
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- Squarrose knapweed
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- Yellow flag iris
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- White bryony
Aquatic Weeds
Quick Facts:
- Plant decay during the summer can result in low-oxygen conditions that stress fish
- Reproduces primarily by turions that are 60 to 80 % germinal and viable for several years
- Plant fragments on boats and trailers allow long-distance dispersal; long-distance dispersal is also possible by turions
- Aquatic perennial; begins to sprout in late fall and can grow through the winter; begins to break up in summer, scattering the turions
Control:
- Contact the Twin Falls County Noxious Weed Department for control methods
Quick Facts:
- Introduced from Eurasia as an aquarium plant
- Forms dense subsurface or surface mats
- Disperses by means of floating stem fragments, by rhizomes, and possibly by waterfowl
- Seed longevity not reported
- Submerged aquatic perennial; stem to 13-22 feet long, branching near the water surface; finely dissected, featherlike leaves
Control:
- Contact the Twin Falls County Noxious Weed Department for control methods
Quick Facts:
- Native to Asia; introduced as an aquarium plant
- Considered the most problematic aquatic plant in the U.S.
- Reproduces by specialized buds in leaf axils, tubers attached to roots, and above and belowground stems
- Disperses by means of buds floating with the current; tubers provide for short-distance dispersal
- Seed longevity not reported
- Submerged aquatic perennial with slender branched stems up to 25 feet long; forms dense stands or subsurface mats
Control:
- Contact the Twin Falls County Noxious Weed Control Department for control methods
Quick Facts:
- Tends to prefer moist or saturated soils and reproduces primarily by seed. A mature plant can produce as many as 2 million seeds that can remain viable for up to 3 years
- Will jeopardize various threatened and endangered native wetland plants and wildlife by eliminating natural foods and cover
- Establishment in irrigation systems can impede the flow of water
Control:
- The shallow woody root system forms a dense mat in the soil, making it difficult to pull. The plant will re-sprout if you do not remove the entire root. Young plants are easier to control by pulling
- If you mow plants, keep in mind that cut stem pieces can send out roots and establish new plants. Frequent mowing can be effective if the cut stems dry rapidly
- Large rootstocks like within 12 inches of soil surface and are susceptible to any form of crop culture that includes annual tillage
- There are three insects available that specifically target this plant. Two types are leaf eaters and one borer. Releases of the insects can be beneficial in hard to reach areas that see little to no disturbance
- Herbicides such as Rodeo, Escort, Habitat, or Garlon are labeled for use and can be applied to actively growing plants, generally before seed set. Always read and follow the label when using any herbicide.
Quick Facts:
- A free-floating, freshwater plant that has the ability to form large, dense mats within waterbodies
- Flowers are purple with 6 petals, one with a yellow diamond-shaped patch outlined with a deeper purple
- Flowers emerge from single spike containing 8-15 flowers
- Roots are dark and feathery, growing up to 3 feet long
Control:
- Contact the Twin Falls County Noxious Weed Control Department for control methods
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- Curlyleaf pondweed
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- Eurasian watermilfoil
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- Hydrilla
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- Purple loosestrife
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- Water hyacinth
Twin Falls County Watch for List
Quick Facts:
- Is a non-palatable, aggressive weed with allelopathic properties (it produces chemicals which inhibit growth of other plants). It becomes a major problem because Dyers Woad over takes native grass, and most livestock and wildlife won’t graze it
- Plants occur in areas with poor, dry soils such as roadsides, rangelands, vacant lots, and open forests
- Was once known as a source of blue dye (indigo) in the 13th century, and it was widely cultivated in England until 1930. Establishment in the U.S. is traced to the early 1900’s as a contaminate in alfalfa seed
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
- In small isolated areas, cutting, mowing, and hoeing, before full flower, can be effective. These methods may need to be repeated throughout the growing season. Field tillage is also effective for short term control. It is important to keep this weed from producing viable seed
- Herbicide products such as Escort and Telar are effective when applied to actively growing plants. Other products such as those containing 2,4-D or Dicamba have also been used. Treatments should be applied during the rosette through bolt stage. Always read and follow the label when using any herbicide
Quick Facts:
- Introduced
- Sold commercially for use in garden pools
- A problem in the Great Lakes and in Flathead Lake, Montana
- Reproduces from rhizomes and seeds
- Small seeds disperse more than 100 yards in flowing water
- Aquatic perennial; emerged or submersed plants grow to 5 feet tall and form dense stands
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
Quick Facts:
- Reproduces readily by seeds that have a high germination rate and may remain viable in the soil for at least seven years. Its seed capsules open explosively, dispersing seed up to 15 feet from the parent plant. It also has an extensive root system
- Is extremely difficult to eradicate because of its persistent nature and ability to regenerate from small pieces of root. It is an aggressive invader and , once present, can completely overtake large areas of open land
- Produces a milky latex that is poisonous to some animals and can cause blistering and irritation on skin. The digestive tract is similarly affected when this plant is eaten. In cattle it causes scours and weakness. When ingested in larger amounts, it can cause death. Cattle usually refuse to eat Leafy spurge unless it is given to them in dry, weedy hay, or when better forage is not available
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
- A well-developed food storage system in leafy spurge roots enables the plant to tolerate cultivation and frequent mowing. Small areas can be managed by digging or hoeing, however, this will only stop the plant from producing viable seed. Direct contact by hand pulling is not advisable due to the milky sap present in the plant
- Herbicides can be effective if applied in June, when the flowers and seeds are developing, or in early to mid-September, when the plants are moving nutrients downward into the roots. Preliminary research suggests that chemical treatment in the fall followed by a spring burn to reduce seed germination and may be an effective strategy for reducing leafy spurge infestations. Multiple herbicide treatments are often necessary every year for several years, making control an extremely expensive undertaking. If left uncontrolled for a single year, leafy spurge can re-infest rapidly. Historically, the most cost-effective herbicide treatment has been a tank mix of Tordon (picloram) at 1 to 2 pints per acre plus 2,4-D at 1 quart in June during flowering and repeated annually. Tordon is a restricted use herbicide and can only be obtained and applied by a licensed applicator. Banvel, Krenite S, Roundup, and Plateau are other products labeled for use. No single treatment will eradicate this weed. Always read and follow the label when using any herbicide.
Quick Facts:
- Introduced from South America as an aquarium plant and pond ornamental
- Develops colonies that from large sub surface or surface mats
- Floating stem fragments establish new plants; potentially long-distance dispersal
- Seed longevity not reported
- An emersed perennial with stems up to 15 feet long
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
ON EDRR LIST
Quick Facts:
- Native to southern Europe
- Toxic to horses, causing “chewing disease”
- Reproduces by seed that disperses short distances from the parent plant
- Seeds are viable for at least 3 years
- Acts as an annual or perennial; grows to 3 feet tall from a stem that bolts in spring to early summer
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
Quick Facts:
- Native to Europe
- All parts of the plant are poisonous, but especially the root
- Disperses long distances by birds; check areas where birds perch
- Longevity not reported
- Climbing perennial vine up to 50 feet in length with tendrils
Control:
- Contact the Twin Falls County Bureau of Noxious Weed control office immediately if spotted!
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- Dyer’s woad
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- Flowering Rush
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- Leafy spurge
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- Parrot feather milfoil
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- Purple starthistle
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- White bryony
