Thistle, bull (Cirsium arvense), milk (Silybum marianum), musk (Carduus nutans), Scotch (Onopordum acanthium), woolly distaff (Carthamus lanatus), and smooth distaff (Carthamus baeticus)

2,4-D

Rate 1.5 to 2 lb ae/a

Time Spring or fall.

Remarks Use fall treatments to control rosettes of these biennial weeds. Use spring treatments before flower stalk elongates. Annual treatments are needed to control seedlings. Pasture legumes are injured or eliminated at these rates.

Caution Avoid drift to sensitive crops.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

aminocyclopyrachlor + chlorsulfuron (Perspective)

Rate 1.8 to 3.2 oz/a aminocyclopyrachlor + 0.7 to 1.3 oz/a chlorsulfuron (4.5 to 8 oz/a of product)

Time Apply to actively growing plants in spring.

Remarks Adjuvants can be used; these include methylated seed oils 0.5 to 1% v/v, nonionic surfactants at 0.25 to 1% v/v, and crop oil concentrates at 1% v/v. Can be applied using an invert emulsion rather than water.

Caution Even low rates can kill nontarget tree and shrub species, so avoid application within a distance equal to the tree height of the sensitive species. Do not allow spray to drift off target. Can injure several grass species including bromes, as well as basin wildrye.

Site of action (aminocyclopyrachlor) Group 4: Synthetic auxin; (chlorsulfuron) Group 2: ALS inhibitor

Chemical family (aminocyclopyrachlor) Pyrimidine carboxylic acid; (chlorsulfuron) Sulfonylurea

aminopyralid (Milestone)

Rate 0.75 to 1.25 oz ae/a (3 to 5 fl oz/a Milestone)

Time Apply in spring or early summer to rosettes or bolting plants or in fall to seedlings and rosettes.

Remarks A nonionic surfactant at 1 to 2 quarts per 100 gal of spray enhances control under adverse environmental conditions.

Caution Do not allow drift to desirable vegetation. Many forbs (desirable broadleaf plants) can be seriously injured or killed. Do not exceed 7 fl oz/a Milestone per year.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

chlorsulfuron (Telar)

Rate 0.75 oz ai/a (1 oz/a)

Time Apply to young, actively growing weeds.

Remarks Do not apply to frozen ground. Maintain constant agitation while mixing product with water. Add 0.25% by volume of nonionic surfactant to spray mixture.

Caution Avoid contact with sensitive crops. Do not treat powdery, dry soils and light, sandy soils if rain is not likely after treatment. Labeled for use on pasture, range, Conservation Reserve Program (CRP), and non-cropland only.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

clopyralid + 2,4-D amine (Curtail)

Rate 1 to 5 quarts/a Curtail

Time Apply to actively growing thistle after most basal leaves emerge but before bud stage.

Remarks Lower rate for in-crop cereal grain application, higher rates for fallow, postharvest, and Conservation Reserve Program (CRP) applications. Consult label for specific directions. With CRP applications, for established grass only. For best results, wait at least 20 days after application before disturbing treated areas (cultivation, mowing, fertilization with shank-type applicators) to allow thorough translocation. Apply in enough total spray volume to ensure good coverage.

Caution See label for crop rotation restrictions before use. Several crops may be injured up to 4 years after application.

Site of action (both) Group 4: synthetic auxin

Chemical family (clopyralid) Pyridine; (2,4-D) Phenoxy acetic acid

clopyralid (Stinger or Transline)

Rate 0.09 to 0.375 lb ae/a (0.25 to 1 pint/a). Labeled rates vary with crops.

Time Up to the bud stage of thistles.

Remarks Best if applied to actively growing weeds. See labels for registered sites.

Caution Consult label for crop rotation restrictions before using these products. Several crops may be injured up to 4 years after application.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

dicamba (Banvel, Rifle, or Clarity)

Rate 0.5 to 1 lb ae/a

Time Apply before flower stalk lengthens on established plants and for seedling control. Spray fall applications to control rosettes.

Remarks Repeat applications for several years to control new seedlings.

Caution Dicamba residues may be in soil for 12 to 18 months after applying. Grass tolerates dicamba at these rates.

Site of action Group 4: synthetic auxin

Chemical family Benzoic acid

diflufenzopyr + dicamba (Overdrive)

Rate 0.175 to 0.35 lb ae/a (4 to 8 oz/a)

Time Apply to the rosettes.

Remarks Use higher rates on thistles that have bolted. Add a surfactant, either nonionic or methylated seed oil, to the spray mix.

Caution Avoid drift to sensitive crops. Will kill legumes.

Site of action (diflufenzopyr) Group 19: inhibits indole acetic acid transport; (dicamba) Group 4: synthetic auxin

Chemical family (diflufenzopyr) Semicarbazone; (dicamba) Benzoic acid

glyphosate + 2,4-D (Campaign)

Rate Broadcast: 16 to 32 fl oz/a. Spot treatment: 1 to 2% solution.

Time Apply to thistles in rosette stage of growth in spring or before freeze-up in fall.

Remarks This product is recommended for musk thistle control in rangeland, pasture, and non-croplands and for the control of those weeds listed on the product label.

Caution Do not graze lactating dairy animals on treated grass within 7 days after application. Animals being finished for slaughter and grazing in the treated area within 30 days of treatment must be removed from the treated area 3 days before slaughter. Do not cut forage for hay within 30 days of application. No grazing restriction if product is used for spot treatments in less than 10% of the total grazed area.

Site of action (glyphosate) Group 9: inhibits EPSP synthase; (2,4-D) Group 4: synthetic auxin

Chemical family (glyphosate) none generally accepted; (2,4-D) phenoxy acetic acid

metsulfuron (Escort and others)

Rate Escort: 0.6 oz ai/a (1 oz/a)

Time Apply postemergence to actively growing plants.

Remarks Using a nonionic or silicone surfactant increases effectiveness. Certain biotypes of musk and Scotch thistle are more sensitive than others to metsulfuron. Application sites differ between products; consult labels.

Caution Apply only to pasture, rangeland, and non-crop sites.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

picloram (Tordon)

Rate 0.25 lb ae/a

Time Apply in the fall before thistle bolts.

Remarks Do not use on diversified cropland. Follow-up applications will be necessary to control new seedlings and escaped plants.

Caution Most formulations are restricted-use herbicides. Soil residuals may last over 1 years after a 0.25 lb ai/a application. Do not contaminate water. Potatoes, beans, and many other broadleaf crops are sensitive to picloram. Do not use in diversified cropping areas.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

triclopyr + clopyralid (Quali-Pro 2,D Herbicide)

Rate 1.5 to 2 pints/a

Time Apply to actively growing thistle from rosette to early bolt stage.

Remarks Add a nonionic surfactant at surfactant manufacturer's recommended rate. Apply in at least 10 gal/a water by ground.

Caution Do not exceed 4 pints/a per year. Do not allow drift to desirable vegetation. Note label restrictions on overseeding or reseeding.

Site of action (both) Group 4: synthetic auxin

Chemical family (both) Pyridine