Hybrid Cottonwood (Hybrid Poplar) Grown for Pulp

Ed Peachey
Revised: 
March 2021

2,4-D amine (many trade names)

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

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

Remarks Controls emerged broadleaf weeds. Glyphosate may be tank-mixed in preplant applications to broaden weed control. May be applied through wick applicators or conventional ground sprayers.

Caution Do not let 2,4-D contact leaves or green tree bark. Avoid drift. Do not apply within 2 days after an overhead sprinkler irrigation or rain, and do not irrigate for 3 days after treatment.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

clopyralid (Transline, Stinger, Bite, and other trade names)

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

Time Apply to new plantings only after they have several inches of new, healthy growth. Apply as a broadcast spray over the trees, or as a banded or directed spray.

Remarks Mustards, henbit, chickweed, kochia, groundsel, lambsquarters, pigweed, Russian thistle, and bindweed will not be suppressed or controlled. Multiple applications may be made as long as total does not exceed 0.5 lb ae/a (1.33 pints/a). Make application to new plantings only after they are well established as indicated by several inches of new healthy growth.

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 to new plantings only after they have been watered and the soil has been packed and settled well around the tree roots. Apply as a broadcast spray over the trees or as a banded or directed spray.

Remarks May be applied during site preparation and establishment or to established trees. Make sure planting slit is well closed and herbicide does not contact tree roots. Apply prior to weed emergence.

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 to new plantings only after they have been watered and the soil has been packed and settled well around the tree roots. Apply prior to weed emergence.

Remarks May be applied during planting and or after trees are established. Make sure planting slit is well closed and herbicide does not contact tree roots. Rain or overhead irrigation is necessary to move the herbicide into soil.

Site of action (dimethenamid-p) Groups 15: inhibits cell growth; (pendimethalin) Group 3: microtubule assembly inhibitor

Chemical family (dimethenamid-p) Chloroacetamide; (pendimethalin) Dinitroaniline

diuron (Direx and other trade names)

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

Time Apply before weeds emerge, or while they are small, before or after planting trees

Remarks Labels may differ among products. Use lower rates on coarse soil. Rain or overhead irrigation is necessary to move the herbicide into soil. May apply prior to or after planting. If applying before planting, prevent treated soil from coming in contact with roots during the planting operation. If buds are beginning to swell, direct application, and use shields to keep spray off of buds and any green tissue. 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. Injury may result from applications to poplar plantings grown on sandy soil with low organic matter with sprinkler irrigation Do not apply to stressed trees; injury may occur. Do not apply to frozen soils.

Site of action Group 7: photosystem II inhibitor

Chemical family Substituted urea

flumioxazin (SureGuard)

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

Time Apply during site preparation prior to transplanting, or over the top of trees prior to budbreak in the spring or after dormancy in fall (release treatment).

Remarks Rain or overhead irrigation is necessary to move the herbicide into soil. Mechanical incorporation is not recommended. For optimal weed control, apply before weed emergence or after a burndown herbicide has controlled existing vegetation.

Caution Transplant operations must take place at least 3 months after application. Do not apply this product over the top of trees after budbreak or leaf spotting and defoliation may occur.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family N-phenylphthalimide

glufosinate (Finale VU)

Rate 0.5 to 1.5 lb ai/a, depending on weed species and size.

Time Apply before planting, for site preparation.

Remarks May be used to control weeds before planting. Prepare ground early to allow maximum weed emergence. May include methylated seed oil (MSO) at 1% v/v or non-ionic surfactant (NIS) at 0.25% v/v spray solution. The addition of 8.5 to 17 pounds of ammonium sulfate (AMS) per 100 gal of water may result in better weed control.

Caution May plant as early as 12 hours after application.

Site of action Group 10: inhibits glutamine synthetase

Chemical family Phosphinic acid

glyphosate (many trade names)

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

Time Apply before planting, for site preparation.

Remarks May be used to control weeds before planting. Prepare ground early to allow maximum weed emergence. 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 XP and other trade names)

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

Time Apply prior to planting or over the top after planting, before seedlings have broken dormancy (prior to bud break), and after soil has settled around the roots.

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 is not recommended when applying over the tops of trees. When applying after planting, make sure adequate rainfall has occurred to close planting slit and close soil around the roots. Do not apply to trees under stress from low fertility, disease, insect damage, severe weather conditions, or water-saturated soils; tree injury or death 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 2XL, Galligan 2E, and other trade names)

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

Time Apply after planting to dormant cottonwood cuttings.

Remarks Direct spray to base of cottonwood tree. For best control, apply before weeds emerge. Adding 1 quart/100 gal spray mix of nonionic surfactant enhances control of emerged weeds.

Caution Applications after bud break may injure crop.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Diphenylether

paraquat (Gramoxone, Firestorm)

Rate 0.5 to 1 lb ai/a

Time Apply before planting, for site preparation.

Remarks May be used to control weeds before planting. Prepare ground early to allow maximum weed emergence. Good spray coverage is essential for good weed control. Plant with minimal soil disturbance. Add 1 pint of nonionic surfactant or 2 pints of crop oil concentrate to 100 gal of spray mix. Apply in at least 20 gal/a spray volume.

Caution Paraquat is a restricted-use herbicide.

Site of action Group 22: photosystem I electron diversion

Chemical family Bipyridilium

pendimethalin (Pendulum Aquacap and other trade names)

Rate 2 to 4 lb ai/a

Time Apply after planting, before weed seed germinates.

Remarks Will not control established weeds. Apply after planting when soil around trees has settled. Rate applied determines the length of residual control.

Caution Do not let pendimethalin contact developing roots, because roots may be stunted.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

quizalofop P-ethyl (Assure II)

Rate 0.034 to 0.068 lb ai/a (5 to 10 fl oz/a)

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

Remarks May be applied over poplars at planting, to aid in establishment. Always use either a nonionic surfactant at 1 quart/100 gal or a petroleum-based crop oil at 1 gal/100 gal.

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

Chemical family Aryloxyphenoxy propionate

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

saflufenacil (Detail)

Rate 0.022 to 0.13 lb ai/a (1 to 6 fl oz/a product)

Time Apply at least 2 months prior to planting trees.

Remarks Include methylated seed oil (MSO) at 1% spray volume. Does not control grass weeds. Rain or overhead irrigation is required to move herbicide into soil. Rate used will determine the length of residual control. Can be applied with glyphosate to improve speed of burndown and control of some glyphosate-tolerant species, such as horseweed.

Caution Do not apply over the top of trees or severe injury will occur. Observe buffer zones on label to avoid drift injury to sensitive crops and other vegetation.

Site of action Group 14: protoporphyrinogen oxidase inhibitor

Chemical family Pyrimidinedione

sulfometuron (Spyder, Oust XP and other trade names)

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

Time Apply to soil surface at least 3 days before transplanting or to 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, Sinbar WDG)

Rate 0.8 to 1.6 lb ai/a

Time Apply in late winter or early spring before weeds emerge, or while weeds are small. May apply before or after planting, but prior to bud swell. If applying after planting, allow soil to settle well around roots before application. May use only as a directed spray after bud swell.

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 frozen soils. If applying after bud swell, keep spray off of foliage, and apply as a directed spray only. 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 0.5 to 1 lb ai/a

Time Apply before planting and thoroughly incorporate into top 2 to 3 inches of soil by cross-disking or rototilling.

Remarks Apply to trash-free and clod-free soil. Rate of application depends on soil type and organic matter. Incorporate into soil within 4 hours of application using equipment that ensures thorough soil mixing. Granular formulations may be activated with 0.5 inches 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