Gumweed (Grindelia squarrosa)

2,4-D LV ester

Rate 2 lb ae/a

Time Apply in early spring when new growth and seedlings are fully emerged.

Remarks After plants reach the bloom stage, control decreases.

Caution Avoid drift to sensitive crops.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

dicamba (Banvel, Rifle, or Clarity)

Rate 0.5 lb ae/a

Time Apply in early spring from emergence to flower bud stage.

Remarks May be mixed with 2,4-D to get better control.

Caution Avoid drift to sensitive crops.

Site of action Group 4: synthetic auxin

Chemical family Benzoic acid

metsulfuron (Escort and others)

Rate Escort: use 0.6 to 1.2 oz ai/a (1 to 2 oz/a)

Time Apply to actively growing gumweed in the spring.

Remarks Using a silicone or nonionic surfactant enhances control. Application sites differ among products at the above rates; consult labels.

Caution Do not let spray drift onto sensitive crops. 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 early spring after plants have emerged.

Caution Most formulations are restricted-use herbicides. See label for grazing restrictions. Avoid drift to potatoes, beans, and many other sensitive broadleaf crops. Do not contaminate water. Do not use picloram in diversified crop areas.

Site of action Group 4: synthetic auxin

Chemical family Pyridine