Established Plantings-Winter Applications that Persist in Soil

atrazine (several products)

Rate 2 to 4 lb ai/a (4 to 8 pints/a Atrazine 4L)

Time Apply February through March to dormant trees. Apply atrazine before annual weeds are 1.5 inches tall; use higher rates for quackgrass control.

Remarks Requires more moisture than Velpar to activate. Do not exceed 4 lb ai/a per year.

Caution A restricted-use herbicide.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazinone

dichlobenil (Casoron CS)

Rate 1.96 to 3.92 lb ai/a (1.4 to 4.3 gal/a)

Time Apply midwinter immediately before a cold rain, to reduce volatility and enhance weed suppression.

Remarks Liquid formulation of encapsulated crystals of dichlobenil. Controls most germinating seeds and seedlings of annual and perennial grasses and broadleaf weeds.

Caution Use only around well-established plants; typically wait until 1 year after transplanting. Do not use on light sandy soils. Do not apply with high or gusty wind, high temperatures, low humidity, or temperature inversions. Grazing livestock is prohibited. Inhibits cellulose and cell wall formation.

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

Chemical family Nitrile

Dithiopyr (Dimension 2EW)

Rate .35 to .5 lb ai/a (1.5 to 2.0 pints /a)

Time Apply for preemergent control of listed grasses and broadleaf weeds. Directed spray only

Remarks Has post emergent control of crabgrass at up to 5 leaves per plant.

Caution Optimum control when made to soil that is free of weeds and clods. Avoid soil disruption after application

Site of action Group 3: microtubule assembly inhibitor

Chemical family dinitroaniline

flufenacet + metribuzin (Axiom DF)

Douglas-fir and true firs only; Supplemental label Oregon only

Rate 12 to 20 oz/a

Time Apply pre- or very early postemergence to weeds when trees are completely dormant. Trees must be established at least one growing season.

Remarks SLN label OR-150015.

Caution Do not apply more than once per production year or within 11 months of last treatment. Both herbicides may contaminate ground water if soil is permeable or water table is shallow.

Site of action (flufenacet) Group 15: inhibits very long chain fatty acid synthesis; (metribuzin) Group 5: photosystem II inhibitor

Chemical family (flufenacet) oxyacetamide; (metribuzin) triazinone

flumioxazin (SureGuard and others)

Rate 0.25 to 0.38 lb ai/a (8 to 12 oz/a SureGuard). Refer to organic matter, soil types, and rates listed on label for various broadleaf weeds.

Time Pre- or postemergence (weeds up to 2 inches tall). Preferred time is fall, to maximize the potential for rain to activate and set the herbicide. Tank mix with approved herbicides if weeds are large, or if weedy vegetation will keep SureGuard from reaching the soil surface.

Remarks Residual or postemergence weed control can be achieved by adjusting rates or labeled tank-mixes (see label). Use a surfactant to improve postemergence control.

Caution Do not apply over the top of nondormant trees unless injury can be tolerated. Use of adjuvants is not recommended.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Diphenylether

hexazinone (Velpar and others)

Rate 1 to 2 lb ai/a (1.33 to 2.6 lb/a Velpar DF, 4 to 8 pints/a Velpar L), depending on soil texture and tree age.

Time Apply in spring before conifer bud break.

Remarks Requires some moisture to activate in soil but less than required for atrazine. Consult label for specific doses and precautions depending on type of soil and soil organic matter content. If trees are growing actively, apply as a directed spray to reduce chance of injury. Later applications in early April may be more effective than March applications due to greater leaching from spring rains.

Caution A restricted-use herbicide in Washington. Label cautions that this herbicide may contaminate ground water if soil is permeable, or water table is close to the soil surface.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazinone

hexazinone + sulfometuron (Westar DG)

Production discontinued in 2018

Rate 1 to 1.5 lb/a Westar DG, depending on soil texture and tree species; consult label

Time Apply either before or soon after weeds emerge, when weeds are small and actively growing. Apply broadcast only to dormant trees. If trees have broken dormancy, directed applications are required to avoid contact with new growth.

Remarks Recommended for Douglas-fir, Fraser fir, grand fir, noble fir, Nordmann fir, and Turkish fir. For other species, apply first to small areas to determine selectivity.

Caution Hexazinone is a restricted-use herbicide in Washington. Surfactants are not recommended and may cause excessive injury. For maximum safety to grand fir, use large transplant stock and apply at 1 to 1.25 lb/a, or use after trees have been established at least one growing season. In newly transplanted fields, rain or irrigation should have settled soil. Use low rates on soils with low organic matter and course structure. Label cautions that this herbicide may contaminate ground water if soil is permeable, or water table is close to the soil surface. Significant carryover potential. Must wait at least one year after last application before planting most other crops, and then use a field bioassay to determine crop safety.

Site of action (hexazinone) Group 5: photosystem II inhibitor; (sulfometuron) Group 2: acetolactate synthase (ALS) inhibitor

Chemical family (hexazinone) triazinone; (sulfometuron) sulfonylurea

indaziflam (Marengo)

Rate 0.047 to 0.063 lb ai/a (7.5 to 15.5 oz/a Morengo), depending on soil texture

Time Apply prior to weed seed germination, in fall to early spring, to firmed soil that does not have cracks.

Remarks Existing vegetation must be controlled with glyphosate or burndown herbicides such as glufosinate. Controls annual broadleaf and grass weeds and perennial weeds from seed only. Existing perennial/biennial weeds growing from roots will not be controlled. Rainfall or irrigation of .25 inch or more within 3 weeks of application is required for maximum efficacy.

Caution Avoid direct contact with foliage, green bark, or roots of desired species. Clean spray tanks thoroughly after use. Make sure soil is settled around trees and there are no cracks. Surface and groundwater advisories are included on the label because of potential harm to nontarget organisms and potential for runoff and percolation to ground water. A well maintained and level vegetated buffer strip of 25 ft or more will help reduce runoff. Application of indaziflam 48 or more hours before rain is forecasted will reduce runoff potential.

Site of action Group 29: inhibits cellulose biosynthesis

Chemical family Alkylazine

isoxaben (Gallery 75DF, Gallery T&V and others)

Rate 0.495 to 0.998 lb ai/a (0.66 to 1.33 lb/a)

Time Apply to debris-free soil surface in late summer to early fall, in early spring, or immediately after cultivation.

Remarks Identify weeds and adjust rates according to charts on label. Activate with 0.5 inch water or shallow cultivation before weeds begin to emerge. Chemical stability remains adequate when left on soil surface for 21 days.

Caution Do not apply to newly transplanted crops until soil settles.

Site of action Group 21: inhibits cell wall biosynthesis Site B

Chemical family Benzamide

isoxaben + trifluralin (Snapshot 2.5TG and others)

Rate 2.5 to 5 lb ai/a (100 to 200 lb/a)

Time Apply to weed- and debris-free soil.

Remarks Activate within 3 days using 0.5 inch of water or shallow cultivation before weeds begin to emerge. Follow label instructions for repeat treatments.

Site of action (isoxaben) Group 21: inhibits cell wall biosynthesis Site B; (trifluralin) Group 3: microtubule assembly inhibitor

Chemical family (isoxaben) benzamide; (trifluralin) dinitroaniline

oryzalin (several products)

Rate 2 to 4 lb ai/a (2 to 4 quarts/a product)

Time Apply to weed-free soil after transplant, or in spring when 0.5 to 2 inches of rain will activate herbicide.

Remarks Apply over the top of established Christmas trees. Tank mix with glyphosate to control emerged weeds.

Caution Do not apply to Douglas-fir (Pseudotsuga menziesii). Do not apply to seedbeds or seedling transplant beds. Apply only to established plants that have been transplanted into their final growing location for a sufficient period of time to allow the soil to be firmly settled around the roots from packing and rainfall or irrigation.

Site of action (oryzalin) Group 3: microtubule assembly inhibitor

Chemical family (oryzalin) dinitroaniline

oryzalin + benefin (XL 2G)

Except Douglas-fir and eastern hemlock

Rate 200 lb/a (2 to 4 months of weed control) to 400 lb/a (4 to 8 months of weed control)

Time Apply to established Christmas trees before target weed species emerge. Established plantings are those that have been transplanted to their final location, and soil has settled with rain or irrigation.

Remarks Controls winter or summer annual grasses and broadleaves. At least 0.5 inch of rain or irrigation is required to activate herbicides. If rain does not fall in 21 days, cultivate to activate. Does not control emerged species. For maximum efficacy, soil should be free of weeds and clod size small. Do not exceed 800 lb/a per season; allow 2 months between applications.

Caution Not for Douglas fir or eastern hemlock; noble fir not listed.

Site of action (both) Group 3: microtubule assembly inhibitor

Chemical family (both) dinitroaniline

oxyfluorfen (Goal 2XL, Galigan 2E, GoalTender and others)

Rate 1 to 2 lb ai/a (4 to 8 pints/a Goal 2XL & Galigan 2E; 2 to 4 pints/a GoalTender)

Time Apply over trees or as directed spray throughout the year, except when buds and new shoot growth are tender and not yet hardened off.

Remarks Controls small emerged broadleaf weeds with brief soil residual. Perennial and emerged annual grasses are not controlled, although fine fescues may be suppressed. Acts as contact, either directly on broadleaf weeds or at soil surface as weeds emerge.

Caution Do not apply in combination with glyphosate, or other products with oil or surfactant additives, until adequately tested.

Site of action Group 14: inhibits protoporphyrinogen oxidase

Chemical family Diphenylether

oxyfluorfen + penoxsulam (Cleantraxx)

Washington only

Rate 3 to 4.5 pints/a Cleantraxx

Time Apply for preemergent and early post emergent control of herbaceous broadleaf weeds and grasses. Can be applied over trees or as directed spray throughout the year, except when buds and new shoot growth are tender and not yet hardened off.

Remarks Perennial and emerged annual grasses are not controlled, although fine fescues may be suppressed. Absorbed either directly on leaves of broadleaved weeds or at soil surface as weeds emerge.

Caution Do not apply in combination with glyphosate, or other products with oil or surfactant additives, until adequately tested.

Site of action oxyfluorfen- Group 14: inhibits protoporphyrinogen oxidase; penoxsulam- Group 2: inhibition of acetolactate synthase

Chemical family (oxyfluorfen) Diphenylether; (penoxsulam) Triazolopyrimidine

pendimethalin (Pendulum 3.3EC and 2G, AquaCap and others)

Rate 2 to 4 lb ai/a (2.4 to 4.8 quarts/a 3.3EC; 100 to 200 lb/a 2G; and 2.1 to 4.2 quarts/a AquaCap) depending on length of control desired)

Time Apply before weed seeds germinate. Tank mix with glyphosate, glufosinate, or labeled burndown herbicides to control existing vegetation.

Remarks Do not apply during bud swell through flushing. Soil should be free from all established weeds. Water within a few days to activate herbicide before weeds emerge. Make sure soil has settled and roots are not exposed to sprays. Inhibits mitosis in roots and shoots.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

prodiamine (Barricade 4FL and others)

Rate 0.65 to 1.5 lb ai/a (21 to 48 oz/a Barricade 4FL)

Time Apply to weed-free site; follow with 0.5-inch rain or irrigation or shallow incorporation.

Remarks Do not apply during bud swell through flushing. Soil should be free from all established weeds. Water within a few days to activate.

Caution Do not exceed maximum rate listed on label in a 12-month period.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

pronamide (Kerb SC)

Rate 1 to 2 lb ai/a (2 to 4 lb/a 50W) and 2 lb ai/a (2.5 to 5 pints/a SC)

Time Make a single application in fall, before freezing weather.

Remarks Not recommended on trees less than 1 year old. Use higher rates for quackgrass and finer soils. Requires soil moisture to activate. Primarily for grass control. Degraded by microorganisms in warmer weather. SLN labels OR-120019 allows for aerial application of Kerb SC. Inhibits cell division or mitosis.

Caution A restricted-use herbicide. Preharvest interval is 1 year.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Benzamide

simazine (several products)

Rate 2 to 4 lb ai/a

Time Fall or spring.

Remarks Simazine must be applied before weeds emerge. One application per year unless to control quackgrass. Avoid applying over actively growing trees.

Caution A restricted-use herbicide. Wait to apply simazine for at least 1 year after transplanting. In Idaho, do not apply simazine to trees less than 3 years old.

Site of action Group 5: photosystem II inhibitor

Chemical family Triazine