Established Plantings

2,4-D amine (many trade names)

Rate 0.24 to 1.43 lb ae/a (0.5 to 3 pints/a)

Time Apply when weeds are actively growing, preferably before the bud stage of growth on annual weeds and at bud stage of growth for perennials. Repeat treatments may be required for less-susceptible weeds. Some labels restrict use to one broadcast application per year.

Remarks To control emerged broadleaf weeds.

Caution Do not let 2,4-D contact leaves or green tree bark. Avoid drift. Do not apply within 2 days after overhead sprinkler irrigation or rain; do not irrigate for 3 days after treatment. May be applied through wick applicators or conventional ground sprayers.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

clopyralid (Stinger, Transline and other trade names)

Rate 0.125 to 0.25 lb ae/a (0.33 to 0.66 pint/a)

Time Apply as a broadcast, banded or directed spray to established plantings, or to new plantings only after they are well established with several inches of new healthy growth.

Remarks Consult label for list of broadleaf weeds that clopyralid will control. Multiple applications may be made as long as total does not exceed 0.5 lb ae/a (1.33 pints/a). When spot spraying, direct spray to keep it off the foliage, or to contact only the bottom or lower branches.

Caution Avoid drift. Rain or irrigation within 6 to 8 hours of application may reduce efficacy. Carefully follow all rotation crop restrictions and other precautions.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

dichlobenil (Casoron 4G and CS)

Rate 2 to 4 lb ai/a (50 to 100 lb/a 4G, 1.4 to 2.8 gal/a CS)

Time Apply to soil surface from mid-November through mid-February to trees established at least 6 months.

Remarks Spot treatments to control emerged weeds may be made as late as mid-May. Rain is required to move herbicide into the soil. Use is restricted to desert areas of Oregon (2 counties) and Washington (3 counties).

Caution Do not use on trees established less than 6 months. Do not allow granules to stick to tree leaves or to accumulate at soil line around base of stem.

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

Chemical family Nitrile

dimethenamid-P (Tower)

Rate 1 to 1.5 lb ai/a (21 to 32 fl oz/a)

Time Apply as a broadcast spray over the trees or as a banded or directed spray. Apply prior to weed emergence.

Remarks Rain or overhead irrigation is necessary to move the herbicide into soil.

Caution Do not apply during budbreak.

Site of action Group 15: inhibits cell growth and division

Chemical family Chloroacetamide

dimethenamid-P + pendimethalin (Freehand 1.75G)

Rate 1.75 to 3.5 lb ai/a (100 to 200 lb product/a)

Time Apply prior to weed emergence.

Remarks Rain or overhead irrigation is necessary to move the herbicide into soil.

Site of action Groups 15 and 3: inhibits cell growth and division and microtubule assembly inhibitor

Chemical family Chloroacetamide and dinitroaniline

diuron (Direx and other trade names)

Rate 0.8 to 2.4 lb ai/a. Use lower rates on coarse soils (0.8 to 1.6 lb ai/a).

Time Apply before weeds emerge, or while they are small.

Remarks Labels may differ among products. Rain or overhead irrigation is necessary to move the herbicide into soil. If weeds are present at time of treatment, add a surfactant at 1 to 2 quarts/100 gal of solution. If applying after buds have swollen, direct application to keep spray off buds and any green tissue.

Caution Do not use on gravelly soils or on any soil with less than 0.5% organic matter. Sprinkler irrigation might injure trees in coarse soils. Do not apply to stressed trees; injury may occur. Do not apply to frozen soils. Do not plant treated areas to any other crop for 2 years after last application.

Site of action Group 7: photosystem II inhibitor

Chemical family Substituted urea

flumioxazin (Redeagle, SureGuard)

Supplemental label for Oregon, Washington, and Idaho only

Rate 0.25 to 0.38 lb ai/a (8 to 12 oz/a product)

Time Apply preemergence, or early postemergence, before weeds are more than 2 inches tall.

Remarks Include a surfactant when applying to emerged weeds. Rain or overhead irrigation is necessary to move the herbicide into soil. Mechanical incorporation is not recommended.

Caution Do not apply to trees transplanted or established less than 1 year. If applying after bud swelling, injury may occur if spray contacts foliage. Direct applications toward soil and away from any green bark or foliage, and use a spray shield to avoid injury. When applying release treatments do not include any adjuvant or fertilizer. Do not apply more than two applications at 12 oz/a or 3 applications at 8 oz/a per year. Do not re-apply within 30 days.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family N-phenylphthalimide

glyphosate (many trade names)

Rate 1.5 to 3.75 lb ae/a, depending on weed species

Time Apply as a postemergence directed spray or spot treatment to emerged weeds.

Remarks For formulations without surfactant, mix 1 quart or more nonionic surfactant per 100 gal of spray solution. Use surfactant with more than 50% ai. Surfactants with less than 50% ai. require a higher surfactant volume per 100 gal of spray solution. Add ammonium sulfate to spray solution to prevent hard water tie up of herbicide.

Caution Using this product without surfactant may reduce performance. Avoid contact of spray, drift, or mist to green bark or foliage. Desirable trees may be protected by using shields or protective coverings to keep spray solution off bark and foliage. Do not use as an over the top broadcast spray.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

metsulfuron methyl (Escort and other trade names)

Rate 0.3 to 1.2 oz ai/a (0.5 to 2 oz/a product)

Time Apply before trees have broken dormancy (prior to bud break).

Remarks Rain or overhead irrigation is required to move herbicide into soil. Weed control is best when applying just prior to, or shortly after, weed emergence.

Caution Do not apply after bud break. Surfactant not recommended when applying over the tops of trees. Do not apply to trees under stress from low fertility, disease, insect damage, severe weather conditions, or water-saturated soils; tree injury may occur.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

oryzalin (Surflan AS, Surflan Flex )

Rate 2 to 6 lb ai/a

Time Apply to weed-free soil.

Remarks Apply only to established plantings, which the Surflan label defines as those that have been transplanted into their growing location long enough that soil has firmly settled around the roots from packing and rain or irrigation; 0.5 inch of moisture (rain or sprinkler irrigation) needed to activate. Lower rate controls for 2 to 4 months, higher rates for 4 to 12 months. May apply up to 12 quarts/a per year. Allow 2.5 months or more between applications. May apply by chemigation if the irrigation system keeps water under the leaf canopy.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

oxyfluorfen (Goal, Galigan and other trade names)

Rate 1 to 1.5 lb ai/a before bud break.

Time Apply prior to bud swell.

Remarks Direct spray to base of cottonwood tree, and avoid spray or spray mist from contacting any green bark or foliage. For best control, apply before weeds emerge. Adding 1 quart/100 gal spray mix of nonionic surfactant enhances control of emerged weeds. May apply as one application, or as a split application with a total of 1.5 lb ai/a per season. Apply in 50 gal water/a or more to reduce injury to crop.

Caution Applications made after bud break may injure crop.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Diphenylether

pendimethalin (Pendulum Aquacap and other trade names)

Rate 2 to 4 lb ai/a

Time Apply to weed-free soil.

Remarks Will not control established weeds. Rate applied determines length of residual control.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

sethoxydim (Nufarm Sethoxydim SPC, Segment, Segment II)

Rate 0.28 to 0.47 lb ai/a (2.25 to 3.75 pints/a of Nufarm Sethoxydim SPC and Segment, 1.5 to 2 pints/a of Segment II)

Time Apply to susceptible annual or perennial grasses listed on label at optimum use rates based on weed size.

Remarks Identify susceptible grass species. Tolerant grasses include annual bluegrass and all fine fescues. Control often is erratic on grasses stunted or stressed from drought, high temperatures, or low fertility. Segment does not require adding an adjuvant. Check Sethoxydim SPC and Segment II labels for appropriate adjuvants.

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

Chemical family Cyclohexanedione

sulfometuron (Spyder, Oust XP and other trade names)

West of the Cascades in Washington and Oregon only

Rate 0.375 to 0.94 oz ai/a (0.5 to 1.25 oz/a product)

Time Apply to soil surface of dormant trees established for at least 1 year.

Remarks Rain or overhead irrigation required to move herbicide into soil.

Caution Avoid applications from bud swell to leaf drop when trees are actively growing. Do not let spray contact green bud or leaf tissue; injury may result. Limit first use to determine selectivity on specific clone. Do not apply to trees under stress from low fertility, disease, insect damage, severe weather conditions, or water-saturated soils; injury may occur.

Site of action Group 2: acetolactate synthase (ALS) inhibitor

Chemical family Sulfonylurea

terbacil (Sinbar WDG)

Rate 0.8 to 1.6 lb ai/a

Time Apply in late winter or early spring before weeds emerge, or while they are small. For applications after bud swell, keep spray off of foliage, and apply as a directed spray only.

Remarks Use lower rates on coarse soil. Rain or overhead irrigation is needed to move herbicide into soil. If weeds are present at time of treatment, add a surfactant at 1 to 2 quarts/100 gal of solution.

Caution Do not use on gravelly soils or on any soil with less than 0.5% organic matter. Sprinkler irrigation might injure trees in coarse soils. Do not apply to stressed trees; injury may occur. Do not apply to frozen soils. Do not plant treated areas to any other crop for 2 years after last application.

Site of action Group 5: photosystem II inhibitor

Chemical family Uracil

trifluralin (Treflan HFP, Trust and other trade names)

Rate 1 to 4 lb ai/a incorporated into soil. Consult appropriate label for rates. Adjust rate according to weed pressure.

Time Apply before weeds emerge.

Remarks Apply as a directed spray to soil between rows and beneath trees. Apply to trash-free and clod-free soil. Incorporate into soil within 4 hours of application using equipment that ensures thorough soil mixing but will not injure the trees. Granular formulations may be activated with 0.5 inches of rainfall or sprinkler irrigation without the need to mechanically incorporate. Will not control established weeds.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline