2,4-D (many products)
Rate 0.95 lb to 3.8 lb ae/A (2 to 8 pints/A), depending on weed species and formulation.
Time Apply over-the-top as a broadcast treatment when trees are dormant using a low rate, or direct spot sprays toward actively growing weeds before budbreak or after budset during cool weather.
Remarks Read label carefully. Mimics natural plant hormones. Ester formulations tend to be more volatile than amine/choline formulations; use with caution near sensitive plants.
Caution Do not apply over the tops of pine or true firs (Abies spp.)
Site of action Group 4: synthetic auxin
Chemical family Phenoxy acetic acid
asulam (Asulox and others)
Douglas-fir, grand fir, noble fir, and Scotch pines
Rate 3.34 lb ai/A (1 gal/A)
Time For bracken fern control. Apply after bud break and hardening or firming of new tree growth. Bracken should be in full frond prior to treatment.
Remarks Lower than labeled rate usually is effective and is advised. Inhibits cell division or mitosis.
Caution Do not graze treated areas. Aerial applications prohibited.
Site of action Group 18: inhibits DHP synthase step
Chemical family Carbamate
clethodim (Envoy and others)
Douglas-fir, true firs (Abies spp.), and pines
Rate 0.094 to 0.25 lb ai/A (12 to 32 fl oz/A Envoy Plus), depending on grass species
Time Apply post-emergence to actively growing annual or perennial grasses as listed on label.
Remarks Consider environmental and plant growth conditions that affect leaf uptake; see label for guidelines.
Caution Do not exceed 64 fl oz/A per season.
Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family Cyclohexanedione
clopyralid (Stinger, Transline and others)
Rate 0.09 to 0.19 lb ae/A (0.25 to 0.5 pint/A for broadleaf weeds; 0.5 to 0.66 pint/A for difficult-to-control perennials)
Time Apply broadcast over tree tops when broadleaf weeds are growing actively, from emergence to five-leaf stage. For perennials such as Canada thistle, apply after most basal leaves have emerged and before bud stage.
Remarks Apply broadcast, in bands, or over the tops of trees. Avoid using surfactants or crop oils. To avoid needle curling, do not apply during first year after transplanting. Mimics natural plant hormones.
Caution Do not exceed 0.67 pint/A per season or 0.5 pint/A for blue spruce. Do not use on Scotch pine. Do not add surfactant or crop oil. Do not apply in the first year of transplanting because some needle curling has been observed on first year transplants.
Site of action Group 4: synthetic auxin
Chemical family Pyridine
flazasulfuron (Mission)
Oregon and Washington only
Rate 0.033 to 0.045 lb ai/A (2.14 to 2.85 oz/A Mission)
Time Pre- and post-emergence. Apply to broadleaf weeds and grasses less than 4 inches tall and prior to tillering of grasses.
Remarks Directed applications preferred, to minimize risk of crop injury. Must be activated with 0.25 to 0.5 inch of water for pre-emergence control. Pre-emergence efficacy is best when applied to bare soil. Do not disturb the soil after activation. Use an adjuvant for post-emergent applications. Controls wild carrot and rattail fescue.
Caution Do not apply the first year after planting. A 25-foot buffer must be maintained between the point of direct application and the closest downwind edge of sensitive terrestrial habitats (forested areas, riparian areas), freshwater habitats (lakes, rivers, sloughs), and estuarine/marine habitats. No aerial applications.
Site of action Group 2: inhibition of the enzyme acetolactate synthase
Chemical family Sulfonylurea
fluazifop (Fusilade DX)
Rate 0.125 to 0.375 lb ai/A (8 to 24 fl oz/A) depending on weed species present.
Time Apply to actively growing grasses in early spring following ample rain. Check label for recommended maximum growth stages of weeds. Apply as a directed spray with 1% crop oil concentrate or 0.25% nonionic surfactant.
Remarks Identify grasses and adjust rates depending on susceptibility and stage of weed growth as label instructs. Results often are erratic on grasses stressed from lack of vigor, drought, high temperature, or low fertility. More mature grasses and quackgrass can be controlled but may require two applications. Annual bluegrass and all fine fescues resist treatment. Inhibits fatty acid production, cell membranes, and new growth.
Caution Do not tank mix with other pesticides or apply within 5 days of other pesticide treatments. Grazing is prohibited.
Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family Aryloxyphenoxy propionate
glufosinate (Finale ES)
Rate Directed spray application: 0.5 to 1.5 lb ai/A (2 to 6 quarts/A); Spot treatment: 2 to 4 fl oz/1 gal of water
Time Apply to actively growing weeds.
Remarks Do not let spray or drift contact living tissue or green, thin, or un-calloused bark, as injury may occur.
Caution Do not broadcast spray over Christmas trees.
Site of action Group 10: inhibits glutamine synthase
Chemical family Phosphinic acid
glyphosate (numerous product names)
Rate Spray: consult labels
Time Select application equipment to prevent crop injury by directing spray toward base of plants or with selective applicators.
Remarks Adjust concentration depending on equipment, or consult label about rate and time of application, especially for perennial weeds. Additional surfactant or mixing ammonium sulfate as label instructs may improve control of slightly stressed weeds. Avoid contact of spray or mist with foliage or green bark of desirable plants. Inhibits production of three amino acids and protein.
Caution Do not exceed 10.6 lb ai/A per year. To avoid weed resistance, rotate herbicides and weed control practices.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
glyphosate (several products)
Rate Wiper: 33% solution
Time Consult label for best time to apply to specific weeds.
Remarks Avoid contact with desirable vegetation. In severe infestations, reduce equipment ground speed or apply in two directions to ensure contact with wiper.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
sethoxydim (Segment and others)
Rate 0.28 to 0.47 lb ai/A (2.25 to 3.75 pints/A Segment), depending on grass species and height
Time Apply at optimum growth stage listed on the label.
Remarks Identify susceptible grasses. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Resistant grasses include annual bluegrass and all fine fescues; quackgrass can be suppressed. Inhibits fatty acid production, cell membranes, and new growth.
Caution Do not mix or apply with any other pesticide, additive, or fertilizer except as specified on the label.
Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor
Chemical family Cyclohexanedione
triclopyr (Garlon 3A, Vastlan, and others)
Rate 0.75 to 1.875 lb ae/A (2 to 5 pints/A) depending on weed species and formulation
Time Apply in late summer or early fall after trees' terminal growth has hardened off, but before target weeds drop leaves.
Remarks To control woody plants and perennial and broadleaf weeds. Select application equipment to prevent tree injury by directing spray toward base of plants or with selective applicators. Ester formulations are more volatile than amine/choline formulations.
Caution Triclopyr spray solutions can injure needles and branches.
Site of action Group 4: synthetic auxin
Chemical family Carboxylic acid