Postemergence

Ammonium nonanoate (Axxe)

Rate A 10 to 13% volume to volume (v/v) dilution (13 to 16 fl oz per gal water) is recommended for most weed control situations and based on the results.

Time Apply to dry plant material, that will remain dry (no rain/no irrigation) for > 2 hr.

Remarks OMRI certified non-selective herbicide for commercial use. Do not allow spray to contact any green plant parts of desirable plants. Provides control and burndown suppression of annual and perennial broadleaf and grass weeds. Spore producing plants such as mosses and liverworts are also controlled.

Caution Causes serious eye irritation.

Site of action N/A

Chemical family N/A

asulam (Asulox)

Certain juniper and yew species only

Rate 3.34 lb ai/a

Time Apply postemergence treatment only when weeds are between the stages of early seedling and early seedhead formation.

Remarks Use at least 20 gal water. Do not use a surfactant. Controls crabgrass, barnyard grass, and horseweed (Conyza canadensis). Inhibits cell division or mitosis.

Caution Do not reapply within 12 months. Labeled for a limited number of ornamental species; consult label before use.

Site of action Group 18: inhibits DHP synthase step

Chemical family Carbamate

bentazon (Basagran T&O; Broadloom)

Do not use on sycamore or rhododendron

Rate 0.75 to 1 lb ai/a

Time Postemergence control of broadleaf weeds, Canada thistle, yellow nutsedge, and musk thistle.

Remarks Direct sprays toward actively growing weed foliage at weed size described on label. The label lists many species where over the top applications are permitted. Add 2 pints/a crop oil concentrate to enhance activity (see label). Two treatments 7 to 10 days apart may be required for Canada thistle or yellow nutsedge. Temperatures below 55°F, drought, or rain within 8 hours will reduce activity. Inhibits photosynthesis. May be tank-mixed with Tower, Segment and other herbicides.

Caution Do not apply within 1 year of harvest. Do not exceed 2 lb ai/a per season.

Site of action Group 6: photosystem II inhibitor

Chemical family Benzothiadiazole

clethodim (Envoy Plus)

Rate 0.068 to 0.24 lb ai/a (9 to 32 oz/a Envoy)

Time Apply postemergence to actively growing annual or perennial grasses as listed on label. 9 to 16 oz/a for annual grass control; 12 to 32 oz/a for perennial grass control.

Remarks For selective postemergence grass control. Consider environmental and plant growth conditions that affect leaf uptake. Surfactants (NIS or COC) and ammonium sulfate will enhance activity.

Caution Do not exceed 64 fl oz/a per season.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

clopyralid (Lontrel, Cleanslate)

Rate Consult labels

Time Apply when weeds are small and actively growing. For Canada thistle, apply to rosette stage but before bud stage.

Remarks Apply over the top of labeled crops or as spot treatment to well-established plantings.

Caution Restricted-use herbicide in WA. Do not exceed 1.3 pints/a per season. Avoid drift or treatment near susceptible crops or unlabeled and desirable plants.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

flazasulfuron (Mission)

Conifers only, Oregon and Washington only

Rate 0.033 to 0.045 lb ai/a (2.14 to 2.85 oz/a Mission)

Time Pre- and postemergence. Apply to broadleaf weeds and grasses less than 4 inches tall and prior to tillering of grasses.

Remarks May be applied over the top of conifers before spring bud break, or after new growth has sufficiently hardened. Use an adjuvant for postemergent applications. To control cottonwoods, wild carrot, and many grasses. Limited experience in the PNW. Many conifers are listed on the label. For those that are not, treat a small area of the field and evaluate crop safety for 6 weeks before treating the entire field.

Caution Do not apply the first year after seeding. Do not apply to conifer seedbeds. 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.

Site of action Group 2: inhibition of the enzyme acetolactate synthase

Chemical family Sulfonylurea

fluazifop (Fusilade II)

Rate 0.25 to 0.375 lb ai/a (16 to 24 oz/a Fusilade II)

Time Apply to actively growing grasses or within 7 days after irrigation with 0.25% nonionic surfactant.

Remarks For selective postemergence grass control. Identify grasses and adjust rates for susceptibility and stage of growth as on label. Note lists of ornamentals and associated instructions regarding topical versus directed sprays. Results often are erratic if grasses are 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. Do not tank-mix with other pesticides. Inhibits fatty acid production, cell membranes, and new growth.

Caution Do not apply within 5 days of other pesticide treatments. Grazing is prohibited.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Aryloxyphenoxypropionate

glufosinate ammonium (Finale)

Spot or directed spray only

Rate 1 to 1.5 lb ai/a (4 to 6 quarts Finale/a)

Time Apply to thoroughly cover actively growing weeds.

Remarks Avoid all contact with desirable foliage and green bark.

Caution Using adjuvants may impair selectivity and increase potential injury to plants.

Site of action Group 10: glutamine synthase inhibitor

Chemical family Phosphinic acid

glyphosate (numerous products)

Rate Spray: consult the label

Time Apply as a directed spray toward the base of a tree when weeds are actively growing or moving sugars to roots.

Remarks Inhibits production of three amino acids and protein synthesis.

Caution Do not spray green bark, foliage, or root suckers. If repeat applications are necessary, do not exceed a total of 10.6 lb ai/a (10.6 quarts/a) per year.

Remarks Consult label about rate and time of application, especially perennial weeds.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

glyphosate (several products)

Rate Wiper: 33% solution

Time Mix 1 gal product to 2 gal water and wipe weeds, avoiding contact with desirable vegetation.

Remarks In severe infestations, reduce equipment ground speed or apply in two directions to ensure contact with wiper (see remarks above.)

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

paraquat (Gramoxone SL 2.0)

Established stock only

Rate Consult labels; formulations differ.

Time Apply as a directed or directed-shielded application when weeds are small (6 inches or less) and actively growing.

Remarks Add a nonionic surfactant or crop oil concentrate according to label specifications, taking care to avoid anionic formulations that react in the tank to form insoluble precipitates. Avoid contact with stems or leaves of the crop. Acts as contact; absorbs energy produced by photosynthesis forming peroxides that disrupt living cells.

Caution A restricted-use herbicide. Do not ingest or inhale spray mist. Wear protective face shields, respirators, and clothing.

Site of action Group 22: photosystem I electron diversion

Chemical family Bipyridilium

pelargonic acid (Scythe)

For nursery trees and shrubs

Rate 3% to 5% solution to control annual weeds, mosses, and cryptogams; 5 to 7% solution to burn down perennial herbaceous plants.

Time Apply to thoroughly wet foliage, either broadcast to non-crop area or before ornamental crop emerges; or spot treat and trim around ornamentals, trees, flower beds, paths, etc. Most effective when temperature is above 65°F.

Remarks Controls small, actively growing weeds and weakens established weeds by removing susceptible vegetation. Disrupts cell membranes, causing leakage and symptoms of leaf burn.

Site of action Group 26: unknown

Chemical family Carboxylic acid

sethoxydim (Segment)

Rate 0.28 to 0.47 lb ai/a (36 to 60 fl oz/a)

Time Apply at optimum growth stage listed on label, and rate recommended for targeted grass.

Remarks For selective postemergence grass control. Identify susceptible grasses. Results often are 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.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

sulfosulfuron (Certainty)

Rate 1.0 to 2.0 oz/a

Time Best results are obtained when target weeds are actively growing and not disturbed by mowing for at least 2 days before and 2 days after application.

Remarks Selective post-emerge weed control in warm-season turf and ornamentals
Caution Properties of this herbicide are associated with other herbicides that are sometimes detected in ground water. Use in permeable soil and where there is a shallow water table may result in ground water contamination. Highly toxic to non-target plants. Do not apply where surface water is present. Drift and runoff may be hazardous to neighboring plants.

Site of action Group 2

Chemical family Sulfonylurea