Mowing

Tilling/Hand-pulling, etc

Grazing

Since Canada thistle spreads primarily via expanding its root system, grazing of above ground forage has not been proved to be an effective reduction strategy.

However, livestock can be trained to eat Canada thistle; while it will not do anything to prevent root spread, properly timed grazing can be used to reduce seed prooduction by preventing flower formation.

Prescribed burns

Ceutorhynchus litura

Larinus planus

Urophora cardui

Puccinia punctiformis

2,4-D
(Several brand names)

• Rate: 2 qt product/acre (1.9 lb a.e./acre)
• Timing: Postemergence in spring at the pre-bud to early bud stage.
• Remarks: Control with 2,4-D alone is only temporary; therefore, it is commonly mixed with other growth regulator herbicides. Research from Colorado showed control from a spring 2,4-D application followed by fall application with different herbicides. 2,4-D is broadleaf-selective and has no soil activity. Do not apply ester formulation when outside temperatures exceed 80°F.

Aminocyclopyrachlor +
chlorsulfuron
(Perspective)

• Rate: 4.75 to 8 oz product (Perspective)/acre
• Timing: Postemergent to plants before they produce seed.
• Remarks: Perspective provides broad-spectrum control of many broadleaf species. Although generally safe to grasses, it may suppress or injure certain annual and perennial grass species. Do not treat in the root zone of desirable trees and shrubs. May need retreatment for 1 to 2 additional years. Do not apply more than 11 oz product/acre per year. At this high rate, cool-season grasses will be damaged, including bluebunch wheatgrass. Not yet labeled for grazing lands. Add an adjuvant to the spray solution. This product is not approved for use in California and some counties of Colorado (San Luis Valley).

Aminopyralid
(Milestone)

• Rate: 5 to 7 oz product/acre (1.25 to 1.75 oz a.e./acre)
• Timing: Postemergence in spring after all plants have fully emerged (some may be budding) until the oldest plants are in full flower stage. Use the higher rate when applying to flowering plants. Applications are also effective in fall before a killing frost. Use higher rates for older/dense stands or for longer residual control.
• Remarks: May need retreatment for 1 to 2 additional years. Aminopyralid is one of the most effective herbicides for the control of Canada thistle. It is safe on grasses, although preemergence application at high rates can greatly suppress invasive annual grasses, such as medusahead. Aminopyralid has a longer residual and higher activity than clopyralid. Other members of the Asteraceae and Fabaceae are very sensitive to aminopyralid.
  Other premix formulations of aminopyralid can also be used for Canada thistle control. These include Opensight (aminopyralid + metsulfuron; 2.5 to 3 oz product/acre) and Forefront HL (aminopyralid + 2,4-D; 1.5 to 2.1 pt product/acre), both applied at the rosette to bolting stages. The formulation with metsulfuron is not registered for use in California.

Clopyralid
(Transline)

• Rate: 0.67 to 1.33 pt product/acre (4 to 8 oz a.e./acre)
• Timing: Postemergence before the bud stage when most of the basal leaves have emerged. Fall applications are also effective.
• Remarks: One or more treatments per season may be needed for 1 to 3 consecutive years for complete control. Allow at least 20 days after application before disturbing treated areas. While clopyralid is very safe on grasses, it will injure many members of the Asteraceae, particularly thistles, and can also injure legumes, including clovers. Most other broadleaf species and all grasses
  are not injured. Also applied in a premix with triclopyr (Redeem, 2.5 to 4 pt product/acre) to rosette to bud stage Canada thistle.

Dicamba
(Banvel)

• Rate: 4 pt product/acre (2 lb a.e./acre)
• Timing: Postemergence to rosettes. Fall applications are also effective.
• Remarks: Dicamba is a broadleaf-selective herbicide often combined with other active ingredients. It is not typically used alone to control Canada thistle because it is not as effective as other
  herbicides such as aminopyralid, clopyralid or aminocyclopyrachlor.
  Dicamba is available mixed with diflufenzopyr in a formulation called Overdrive. This has been reported to be effective on Canada thistle. Diflufenzopyr is an auxin transport inhibitor which
  causes dicamba to accumulate in shoot and root meristems, increasing its activity. Overdrive is applied postemergence at 4 to 8 oz product/acre to rapidly growing plants. Higher rates should be used when treating perennial weeds. Add a non-ionic surfactant to the treatment solution at 0.25% v/v or a methylated seed oil at 1% v/v solution.

Picloram
(Tordon 22K)

• Rate: 2 pt product/acre (8 oz a.e./acre).
• Timing: Best when applied postemergence to rapidly growing thistle after most leaves emerge but before bud stage. Fall applications are also effective.
• Remarks: Picloram gives a broader spectrum of control than aminopyralid, aminocyclopyrachlor, and clopyralid, and has much longer soil residual activity. Most broadleaf plants are susceptible. Although well-developed grasses are not usually injured by labeled use rates, some applicators have noted that young grass seedlings with fewer than four leaves may be killed. Do not apply near trees. Tordon 22K is a federally restricted use pesticide. Picloram is not registered for use in
  California.

Glyphosate
(Roundup, Accord XRT II, others)

• Rate: Broadcast foliar treatment: 2 qt product (Roundup ProMax)/acre (2.25 lb a.e./acre). Spot treatment: 2% v/v solution
• Timing: Postemergence to rapidly growing thistles when most plants are past the bud stage. Fall applications must be before the first killing frost.
• Remarks: Do not tank-mix other herbicides with glyphosate for thistle control. More than 1 year of treatment may be necessary for complete control. Glyphosate will only provide control during the year of application; it has no soil activity and will not kill seeds or inhibit germination the following season. Glyphosate is nonselective. To achieve selectivity, it can be applied using a wiper or spot treatment to control current year’s plants.

Chlorsulfuron
(Telar)

• Rate: 1 to 1.33 oz product/acre (0.75 to 1 oz a.i./acre)
• Timing: Postemergence from bolting to bloom stages. Can also apply in fall.
• Remarks: Chlorsulfuron has mixed selectivity on both broadleaf and grass species but is generally safe on most grasses. It has fairly long soil residual activity. The herbicide solution requires constant agitation during application.

Imazapyr
(Arsenal, Habitat, Stalker, Chopper, Polaris)

Sulfometuron
(Oust and others)

• Rate: 6 to 8 oz product/acre (4.5 to 6 oz a.i./acre)
• Timing: Apply preemergence or early postemergence before or during the rainy season when weeds are germinating or actively growing.
• Remarks: Sulfometuron has mixed selectivity. It can cause minor damage to some native perennial grasses and has a fairly long soil residual. Higher rates may increase control but will also give more bare ground. Requires 20 inches of annual rainfall or more for effective preemergence control.