Starthistle, yellow (Centaurea solstitialis), purple (Centaurea calcitrapa), and Iberian (Centaurea iberica)

2,4-D LV ester or 2,4-D amine

Rate 1 lb ae/a in 50 gal of water

Time Apply before flowering.

Remarks Foliage must be thoroughly wet.

Caution Avoid drift to sensitive crops.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

aminocyclopyrachlor + chlorsulfuron (Perspective)

Rate 1.2 to 1.8 oz/a aminocyclopyrachlor + 0.5 to 0.7 oz/a chlorsulfuron (3 to 4.5 oz/a of product)

Time Apply to actively growing plants.

Remarks Adjuvants can be used and 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 to plants at the rosette through bolting stages.

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 1.125 oz ai/a (1.5 oz/a). Rate selection is based on weed species and soil texture.

Time For best results apply to young, actively growing weeds.

Remarks For suppression only. Do not apply to frozen ground. Constantly agitate while mixing in spray solution. Add 0.25% v/v nonionic surfactant to the spray mixture. Apply with ground equipment in at least 10 gal/a carrier.

Caution See label for tank-cleaning instructions. Use on non-cropland only.

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

Chemical family Sulfonylurea

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 After most rosettes have emerged but before bud formation.

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

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

Site of action Group 4: synthetic auxin

Chemical family Pyridine

clopyralid + 2,4-D amine (Curtail)

Rate 1 to 5 quarts/a Curtail

Time Apply after most rosettes have emerged but before bud formation.

Remarks Lower rate for in-crop cereal grain application, higher rates for fallow, postharvest, and Conservation Reserve Program (CRP) applications. See label for specifics. With CRP applications, for established grass only. Apply in enough total spray volume to ensure good coverage.

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

Site of action Group 4: synthetic auxin

Chemical family (clopyralid) pyridine; (2,4-D) phenoxy acetic acid

dicamba (Banvel, Rifle, or Clarity)

Rate 1 to 2 lb ae/a

Time Apply when plants are still in rosettes but before flower stems elongate.

Remarks Plants should be actively growing at time of treatment.

Caution Avoid drift to sensitive crops. Follow grazing restrictions.

Site of action Group 4: synthetic auxin

Chemical family Benzoic acid

diflufenzopyr + dicamba (Overdrive)

Rate 0.26 to 0.35 lb ae/a (6 to 8 oz/a)

Time Apply to seedlings or rosettes.

Remarks Add a suitable surfactant 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

picloram (Tordon)

Rate 0.25 to 0.375 lb ae/a

Time In spring, to plants still in rosette through bud formation.

Remarks A selective treatment that will not damage perennial grasses at the suggested rate. Treating at bud stage can reduce weed seed viability by 95 to 100% in the year of application.

Caution Most formulations are restricted-use herbicides. Do not contaminate water. Do not use in diversified crop areas. Potatoes, beans, and many other broadleaf crops are sensitive to picloram.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

triclopyr + clopyralid (Redeem R&P)

Rate 1.5 to 2.5 pints/a

Time Apply from rosette to early bolt stage when starthistle is actively growing.

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. Avoid drift to desirable vegetation. Note label restrictions on overseeding or reseeding.

Site of action (both) Group 4: synthetic auxin

Chemical family (both) Pyridine