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Canada thistle
Life cycle: Noxious statewide. Creeping perennial.
Leaves: Smooth, medium green, spine-tipped, crinkled margin. Smaller than biennial thistle.
Stems: 2 to 5 feet tall, grooved, branching at top.
Flowers: Numerous flowers on branched heads. About ¾ inch. Usually lavender, may be pink or white. Separate male and female flowers.
Roots: 10 to 15 feet deep.
Weed Species: state noxious weed
Comments: Capable of rapid spread. Seed matures 7 to 10 days after first flower color.
Control
Tordon 22K (picloram) Spring or Fall. Primarily for small infestations. Apply 2 qt/A Tordon as a spot treatment. Use a minimum of 20 gpa carrier. Rates above 1 qt/A cannot exceed 50% of an acre. Stands have been reduced 85 to 90% in SDSU tests. Make spring treatments before seed forms. Make fall applications before soil freeze-up. Use 2,4-D or other herbicides to control stragglers or seedlings in succeeding years. The 1 qt/A rate has been promising in recent Canada thistle tests. Use the high rate for maximum stand reduction, especially for fall treating areas such as fence lines. Control one year later is greater than for lower Tordon rates in tank-mixes. Tordon has foliar activity and extended soil residual. It is absorbed into the leaves and controls topgrowth. It also translocates into roots. Rainfall moves the herbicide into the root zone. Trees, legumes, and broadleaf plants are very sensitive to drift and soil residual. Tordon is registered for grass pasture and range, fallow cropland, and noncrop areas. At high rates, bromegrass, buffalograss, and wheatgrass may be severely injured; bluegrass is tolerant. Tordon is formulated as a liquid containing 2 lb/gal acid equivalent. RESTRICTIONS: Do not use in trees. Avoid drift to trees or sensitive broadleaf crops. For rates above 1 qt/A, do not harvest for hay within 2 weeks of treatment. Do not graze dairy animals for 2 weeks after treatment. Remove animals 3 days before slaughter if grazing within 2 weeks after spraying. Do not apply into water or wetlands or on inner banks of irrigation or drainage ditches. Risk of leaching is greatest where soils have rapid permeability (such as loamy to sand) and where the underlying aquifer is near the surface. Restricted Use Pesticide. Tordon 22K + 2,4-D (picloram + 2,4-D) ($15.20) Spring. Intended as a 4- to 5-year program with sufficient seasonal suppression so only one application per season is required. Apply at bud stage before flowers open. Tank-mix 1 pt Tordon plus 1 lb ae 2,4-D or use 4 pt Grazon premix containing .54 lb picloram (Tordon) plus 2 lb 2,4-D amine per gal. Amines cause less leaf burn and are preferred if growth is lush. Minimum carrier is 10 gpa for ground 2 gpa for air. This combination is promising to improve stand reduction over a period of several years. Some fall regrowth may be noted in wet seasons. Lower rates do not provide sufficient residual control into the fall. The tank-mix is registered for noncrop, grass pasture, and range. Grazon may be used only in grass pasture and range. Grass is usually tolerant to these Tordon rates. Some stunting, especially if applied at boot stage, may be noted. RESTRICTIONS: Do not use in trees. Avoid drift to sensitive broadleaf crops. Refer to surface or groundwater pre- cautions as for Tordon alone. Do not graze lactating dairy for 7 days after application. Labels for 2,4-D allow harvesting hay 30 days after application and require a 3 day removal period before slaughter. Restricted Use Pesticide. Milestone (aminopyralid) ($7.50-17.50) Spring. Will control Canada thistle (5-7 oz/A) and perennial sowthistle (3-5 oz/A). Make applications before the bud stage or early flowering. Use higher rates for advanced weed growth stages or under adverse growing conditions, such as drought. Use a non-ionic surfactant (NIS) at 0.25-0.5% (1-2 qt per 100 gallons spray solution) under adverse growing conditions or advanced weed growth stages. Avoid mowing for 7 days after application to allow for herbicide translocation in the weeds. Milestone may be applied to non-irrigation ditch banks and seasonally dry wetlands, but may not be applied over water or to areas where surface water is present. Applications may be made on warm and cool season grasses. RESTRICTIONS: Do not apply more than 7 fl oz (0.11 lb ae) per acre per year for broadcast applications or 14 fl oz (0.22 lb ae) for spot treatments (less than ½ acre areas). There are no grazing restrictions, but aminopyralid may be transferred in manure from livestock grazing on grass that had been sprayed within 3 days. After grass seeding, wait until perennial grasses are well established with a secondary root system before applying Milestone. Some grasses, such as smooth brome, may be suppressed under adverse growing conditions. Stinger or Transline (clopyralid) ($39.90-80.40) Spring. For Canada thistle. Perennial sow thistle suppression. Apply from rosette to bud stage when plants are actively growing. Stinger is labeled for use in grass pasture, rangeland, fallow, fencerows, and other noncrop areas. Transline is labeled for noncrop areas, rangeland, and rights-of-way. Transline is marketed only to government and public agencies. Use 1 to 1.33 pt/A to achieve maximum stand reduction. Data suggest 90 to 95% reduction can be expected. Minimum carrier is 5 gpa; use at least 10 gpa for most ground applications. Stinger or Transline has potential in sites where grass cannot be damaged or where trees limit use of herbicides with harmful soil residual. RESTRICTIONS: Do not contaminate irrigation ditches. No grazing or haying restrictions. Curtail (clopyralid + 2,4-D) ($18.60) Spring. Premix. For Canada thistle. Apply before bud stage when plants are actively growing. Reduced rate of 1 qt/A is frequently used for seasonal suppression. The 2 qt/A rate has provided excellent control and 60 to 70% stand reduction. Minimum carrier is 10 gpa for ground and 5 gpa for air for most situations. Curtail is a premix containing .38 lb clopyralid (Stinger) plus 2 lb 2,4-D amine per gallon. Curtail is labeled for use in noncrop areas, rangeland, grass pasture, and CRP grass seedings and fence lines. RESTRICTIONS: Do not graze lactating dairy cattle in treated areas for 14 days after application. Remove meat animal 7 days before slaughter if grazing within 2 weeks after application. Do not harvest hay within 30 days after application. Redeem (triclopyr + clopyralid) ($47.55) Spring. Premix. Intended for Canada thistle and certain broadleaf weeds not controlled with 2,4-D. Apply 4 pt/A from early growth to bud stage. Weeds must be actively growing. Reduced rates provide seasonal suppression. Minimum carrier is 10 gpa for ground or 3 gpa for air. Redeem is a premix containing 2.25 lb triclopyr (Garlon) plus .75 lb clopyralid (Stinger) per gallon. Redeem is labeled for use in rangeland, grass pasture, roadsides, CRP grass seedings, fence lines, and other noncrop areas. RESTRICTIONS: Do not graze or harvest forage for dairy cattle for 14 days after application. Do not harvest hay until the next growing season for dairy or harvest hay for other livestock for 7 days after treatment. Remove meat animals at least 3 days before slaughter. Do not treat banks or bottom of irrigation ditches. Overdrive (diflufenzopyr + dicamba) ($10.45-20.90) Overdrive is a selective postemergence herbicide for the control or suppression of many annual, biennial, or perennial broadleaf weeds in pasture, rangeland, and noncrop sites. Overdrive controls weeds by auxin transport inhibition. Spring or Fall. Rate is 4 to 8 ounces per acre based on weed species and maturity. Use higher rates for perennial weeds like Canada thistle and sowthistle. A maximum of 10 oz/A can be applied per season in noncropland sites and a maximum of 8 ounces per acre in pasture, hay, and rangeland. Use 1 qt NIS per 100 gal or MSO at the rate of 1.5 to 2 pt/A. Do not use less than 3 gallons of spray volume per acre. Rainfast 4 hours after application. Overdrive may be tank-mixed with several labeled tank-mix partners to improve weed control spectrum. RESTRICTIONS: Do not apply aerially. Do not plant crops for 30 days after last application. Pasture or rangeland grass treated with Overdrive can be grazed or harvested for livestock feed immediately after application. Do not apply to newly seeded grasses or small grains. Dicamba Products (dicamba) ($32.00) Spring or Fall: Spot treatment rate, primarily for small infestations. Use at least 3 gpa carrier for ground or 2 gpa for air. Make spring application at early bud stage. Apply in fall before a killing frost. Results on thistle are consistent. Treatment should exceed 75% reduction the following season. Lower rates provide less permanent reduction. Control is usually greater in low rainfall areas. An application of 2,4-D or other herbicide is required to control seedlings and weakened plants in succeeding years. Refer to Dicamba Products table. Clarity and Vanquish contain a low vapor salt of dicamba. Dicamba is a selective, translocated herbicide. It has foliar activity. Favorable growing conditions improve results. High rates have soil residual extending through one season. Dicamba products are registered for use in pasture, range, and noncrop areas. Bromegrass may be severely stunted; bluegrass and several other grasses are tolerant. Trees, legumes, and broadleaved plants are sensitive to drift and soil residues. RESTRICTIONS: Do not graze lactating dairy for 40 days or harvest hay for 70 days after application of more than 1 qt/A. Slaughter animals must be removed for 30 days after last application. Avoid drift to non-target plants. Do not contaminate water. Spring. Tank-mix. Intended as a 4- to 5- year program with sufficient seasonal suppression so only one application per year is required. Apply at bud stage. Mix dicamba 4L at 2 pt plus 2,4-D at 1 lb ae/A. Amines cause less leaf burn and are preferred if growth is lush. Apply in 10 to 20 gpa carrier. This combination is a promising program to improve stand reduction over a period of several years. It also is a good choice for inaccessible areas where the labor cost of a second application is prohibitive. Lower dicamba rates may not provide sufficient residual control into the fall, especially in wet seasons. Refer to Dicamba Products table. Cimarron Max (metsulfuron + dicamba + 2,4-D) ($6.70-26.80) Use Rate II for suppression of Canada thistle and Rate III for suppression of perennial sowthistle. The Rate II or 10 acre rate provides the equivalent of .5 oz Ally 60DF + .5 pt Banvel 4L + 1.5 pt 2,4-D 3.8L per acre. Rates are based on weed species and weeds less than 4 inches tall. Do not apply more than the equivalent of 1.66 oz per acre of Cimarron Max Part A per year. Add NIS at 2 to 4 pt/100 gal. May be applied by ground or air. No restrictions or waiting period between treatment and grazing for non-lactating animals. Remove meat animals 30 days prior to slaughter. Do not graze lactating dairy within 7 days of treatment. Do not harvest hay for 37 days after treatment. 2,4-D ($5.80-8.70) 1.5 lb ae 2,4-D Amine or Ester (1.5 lb ae) Spring or Fall: Requires a spring and fall application each year. Make spring applications at bud stage. Retreat in September or early October after new fall growth reaches 6 inches. Suggested carrier is 10 to 20 gpa. Results can be variable. One spraying prevents seed production. Two applications provided 10 to 25% stand reduction the first year in SDSU tests. Reductions of 70 to 80% may be achieved after 3 years. Uses for 2,4-D include grass pasture, range, and noncrop areas. This is a popular program for large infestations in pasture and roadsides. However, several years are required to reach high levels of eradication. Amine formulations are suggested for spring treatments when growth is lush. Esters may be used for fall spraying or if plants are stressed. Fall retreating is critical.
($23.15-46.25)
1-2 qt Tordon 2L (.5-1 lb ae)
1 pt Tordon 2L + 1 lb ae 2,4-D (.25+1 lb ae)
4 pt Grazon 2.54L (.27+1 lb ae)
3-7 oz Milestone (0.05-0.11 lb ai)
0.66-1.33 pt Stinger 3L or Transline 3L (.25-.5 lb ae)
2 qt Curtail 2.38L (.19 + 1 lb ae)
4 pt Redeem 3L (1.12 + .38 lb ae)
4-8 oz Overdrive 70DF (.05-.1 + .125-.25 lb ae)
2 qt dicamba 4L (2 lb ae)
Dicamba Products + 2,4-D (dicamba + 2,4-D) ($18.90-19.80)
2 pt dicamba 4L + 1 lb ae 2,4-D (1 + 1 lb ae)
Dicamba plus 2,4-D is labeled for use in grass pasture, range, and noncrop areas. Grass is usually tolerant to these rates; some stunting may be noted, especially if applied at boot stage.
RESTRICTIONS: Do not use in trees. Avoid drift to sensitive broadleaved plants. Labels for 2,4-D do not allow grazing lactating dairy for 7 days after application. Labels for 2,4-D allow harvesting hay 30 days after application and require a 3 day removal period before slaughter. Dicamba labeling for 1 to 2 pt/A restricts grazing lactating dairy for 21 days or haying for 51 days after application. Note other label restrictions for higher rates.
Telar (chlorsulfuron)
1-1.3 oz Telar 75XP (.046-.061 lb ai)
Spring or Fall. For Canada thistle. Apply 1.3 oz Telar DF at bud to bloom or in fall at rosette stage. Spring application preferred. Minimum carrier is 10 gpa. Add NIS at 1 qt/100 gal. May be tank-mixed with 2,4-D, dicamba, or glyphosate products.
RESTRICTIONS: There are no grazing restrictions for rates less than 1.3 oz/A. Labeling does not include hay uses. Do not apply to water, such as lakes, streams, or areas where runoff flows into such areas.
20-5 Acres/.5 oz Part A + 2.5 gal Part B (.01-.038 + .12-.5 + .38-1.5 lb ae)
Cimarron Max herbicide is a twin-pak combination. Part A contains metsulfuron (Ally). Part B contains 1 lb dicamba (Banvel) plus 2.87 lb ae 2,4-D amine per gallon. The use ratio is .5 oz Part A to 2.5 gal of Part B to treat 5 to 20 acres. Refer to following rate table for acres treated.
2-3 lb ae 2,4-D Amine (2-3 lb ae)
Late Fall: Apply a high rate in late fall before leaves are damaged by frost. Rates to 2 lb ae/A may be used in pasture and range; higher rates are allowed in noncrop and fallow. Data indicate 50 to 60% stand reduction if there is considerable new growth and if weeds have been weakened by previous control practices. Light frost before application does not reduce control; temperatures of 60o F. after application improve results.