Horseweed (Marestail) (Conyza canadensis)

2,4-D LV ester

Rate 1 lb ae/a

Time Apply when horseweed is in the seedling to rosette stage of growth.

Remarks Plants should be actively growing at time of treatment.

Caution Avoid drift to sensitive crops and desirable vegetation. This product will injure or kill sensitive broadleaf plants.

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 1 to 1.5 oz ae/a (4 to 6 fl oz/a Milestone)

Time Apply to actively growing plants.

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

clopyralid (Stinger or Transline)

Rate 0.125 to 0.188 lb ae/a

Time Apply to actively growing plants up to the five-leaf stage.

Remarks See label 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 0.25 lb ae/a

Time Apply in the seedling to rosette stage.

Remarks Plants should be actively growing at time of application.

Caution Avoid drift to sensitive crops and desirable vegetation. This product will injure or kill sensitive broadleaf plants.

Site of action Group 4: synthetic auxin

Chemical family Benzoic acid

diflufenzopyr + dicamba (Distinct)

Rate 4 oz/a

Time Apply in the seedling to rosette stage.

Remarks Plants should be actively growing at time of application.

Caution Avoid drift to sensitive crops and desirable vegetation. This product will injure or kill sensitive broadleaf plants.

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

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

flumioxazin (Chateau or Payload)

Rate 2 to 6 oz ai/a (4 to 12 oz/a). Rate depends on application timing and soil type and organic matter.

Time May be applied preemergence or postemergence to small, actively growing horseweed.

Remarks Preemergence treatments require rain to move into the soil. Can be used in several crops.

Caution Note recropping restriction intervals on the label.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family N-phenylphthalimide

glyphosate

Rate 0.75 to 1.5 lb ae/a

Time Apply while horseweed is actively growing and less than 12 inches tall.

Remarks Glyphosate-resistant horseweed is reported throughout the United States.

Caution Controls grasses as well as other vegetation in treated area.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted