Horsetail, field (Equisetum arvense)

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

chlorsulfuron (Telar)

Rate 1 to 1.5 oz ai/a (1.33 to 2 oz/a)

Time May be applied preemergence or early postemergence.

Remarks Do not apply to frozen ground. Maintain constant agitation while mixing in spray solution. Add 0.25% v/v nonionic surfactant to the spray mixture. Application rates up to 1 oz ai/a (1.33 oz/a allowed on pasture, rangeland, and Conservation Reserve Program (CRP) sites. Rates above 1 oz ai/a (1.33 oz/a) allowed only on non-cropland.

Caution Avoid contact with sensitive crops. Do not treat powdery, dry soils and light, sandy soils unless rain is likely after treatment.

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

Chemical family Sulfonylurea

dichlobenil (Casoron)

Rate 4 lb ai/a granular formulation

Time Apply in winter or early spring, when moisture is available to leach chemical into soil. In landscape plantings, apply any time and place bark mulch over the treated area to reduce volatilization.

Remarks Good selective control in many fruits and ornamental plants. Use as a follow-up, supplemental treatment if horsetail resists many soil-applied herbicides. Can apply over labeled ornamental plants or conifer tree nurseries. Apply midwinter immediately before a cold rain to reduce volatility and enhance weed suppression. Weigh and distribute uniformly exact quantities over precisely measured areas. Oregon results over 9 years suggest that perennial weeds can be suppressed with 4-, 3-, and 2-lb ai/a rates applied in 3 consecutive years. Grazing livestock is prohibited. (Inhibits cellulose and cell wall formation.)

Caution See label for precautions on ornamental species and varieties tolerant of dichlobenil.

Site of action Group 20: inhibits cell wall synthesis Site A

Chemical family Nitrile


Rate 1 to 2 lb ae/a

Time Apply when horsetail fully emerges and before grain or grass is in boot stage.

Remarks Gives 20 to 30% reduction in field horsetail stands with each spray application. Re-treatments are necessary and may be most effective with more than one application per year. The second application can be to the stubble after harvesting grain fields.

Caution Apply once or twice per year until horsetail is controlled. Skipping a year means losing the control gained up to that time.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid