2,4-D ester (Weedone LV 6 and many others)
Rate For conifer release apply 0.95 lb ae/A to 2.75 lb ae/A (22 to 64 oz/A product). For site preparation apply 2.75 lb ae/A to 3.78 lb ae/A (44 to 88 oz/A product).
Time For conifer release apply before conifer budbreak in spring. See remarks for Douglas-fir release. For site preparation apply when susceptible plants are leafed out and developing.
Remarks 2,4-D controls a large spectrum of broadleaved weeds and woody plants on forest sites. These include thistles, false dandelion, woodland groundsel, sow thistle, alder, madrone and manzanita species. Amine salt formulations can also be used, but ester products perform better in early spring and on woody species. For conifer release apply in spring before conifers break bud. To control alder only in Douglas-fir plantations apply 2-2.75 pints/A in the late spring as alder is leafing out and up until Douglas-fir bud break. Applications made after bud break are possible until two inches of conifer growth but with increased risk of Douglas-fir injury. Douglas-fir, hemlock, and Sitka spruce are tolerant. True firs, redwood and cedars can show injury at high rates. Larch and ponderosa pine can show variable injury. For site preparation apply in early spring into summer as alder and other plants are fully leafed out.
Caution Consult label to avoid exceeding maximum yearly and single application rate. 2,4-D esters are volatile and damaging vapors can move off site in warm temperatures.
Site of action Group 4: synthetic auxin
Chemical family Phenoxy acetic acid
aminopyralid + metsulfuron (Opensight)
Rate 0.066 to 0.11 lb ae/A aminopyralid + 0.0118 to 0.0195 lb ai/A metsulfuron (2 to 3.3 oz/A product)
Time For site preparation only. Apply when brush plants and hardwoods are fully leafed out from summer through the fall but before leaf coloration. Avoid conifer foliage contact as severe injury will occur.
Remarks State supplemental labels for forest use must be in users possession. The combination of aminopyralid and metsulfuron controls a wide variety of deciduous shrubs and herbaceous plants prior to planting. Rubus species such as blackberries, salmonberry, thimbleberry, and blackcap are especially sensitive. Other species controlled include snowberry, cottonwood, cherry, willow, oak, and ocean spray. Scotch broom can be impacted and the soil activity may help control germinating seedlings. A number of broadleaf weeds are controlled, but thistles, bracken fern and sword fern are the major forestry targets. Consult labels for additional weeds controlled. Add surfactant as specified on the label.
Caution Both active ingredients in Opensight can be damaging to conifers and users should avoid contact with conifer foliage. In addition, aminopyralid has substantial soil activity and applications near conifer roots can result in injury through root uptake. Conifers planted sooner than two months after application west of Cascades or 4 months east of Cascades may be injured.
Site of action Group 4: synthetic auxin (aminopyralid); Group 2: acetolactate synthase (ALS) inhibitor (metsulfuron)
Chemical family Pyridine and Sulfonylurea
clopyralid (Transline and others)
Rate 0.19 to 0.49 lb ae/A (8 to 21 oz/A product)
Time Apply in the spring when susceptible weeds are present and during the growing season for shrubs like elderberry.
Remarks All conifer species appear tolerant to clopyralid at any growth stage for conifer release. For control of bull thistle and small woodland groundsel, use at least 8 oz/A product. In late spring higher product rates up to 21 oz/A may be needed to control larger plants. Canada thistle is best controlled at bud stage in late spring/early summer with rates at 16 oz/A product or higher. Additional sensitive weeds include other thistles, clovers, hawkweeds, yellow starthistle, vetches. Elderberry species can be effectively controlled at rates of 10-12 oz/A when fully leafed out in summer. Clopyralid can be an effective tank mix herbicide with soil active herbicides for herbaceous weed control in plantations. Grasses and many other broadleaved weeds are tolerant.
Site of action Group 4: synthetic auxin
Chemical family Pyridine
glyphosate (Roundup Custom and many others)
Rate 0.75 lb to 1.5 lb ae/A (0.75 to 1.5 quarts/A product) for release; 1.5 to 3 lb ae/A (1.5 to 3 quarts/A product) for site preparation.
Time For release apply over established conifers after dormant buds set in late summer or fall. For site preparation apply during the growing season from late June through September until leaf senescence.
Remarks There are many glyphosate products labeled for forestry use. Products that have no surfactant in the formulation may be safer over conifers for release in the fall. Most conifers have at least some tolerance to glyphosate when dormant. Western hemlock and larch can be injured. Glyphosate can control a wide variety of deciduous shrubs such as salmonberry, thimbleberry, hazel, ocean spray, vine maple, cherry, elderberry, poison oak and many others. Perennial forbs like bracken fern and many grasses and broadleaved weeds are also controlled. For site preparation, apply any time plants are actively growing. Use higher rates and add additional surfactant per label recommendations. Other site preparation herbicides like imazapyr or metsulfuron can be added to broaden activity on complex deciduous plant communities.
Caution Douglas-fir and other conifers can be injured by glyphosate as buds swell and budbreak occurs in the spring or before they harden off and set bud in the fall. Apply to dormant seedlings to mitigate risk of injury.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
imazapyr 4 lb ai/gal (Arsenal Applicators Concentrate and others)
Rate 0.5 lb ae to 0.75 lb ae/A (8 to 12 oz/A product) for Douglas-fir release. Site preparation rate is dependent on conifers to be planted. 0.75 lb ae/A to 1.5 lb ae/A (12 to 24 oz/A product) for Douglas-fir. See remarks for other species planted.
Time For release over Douglas-fir apply after final resting buds have formed in fall. For site preparation apply when brush plants and hardwoods are fully leafed out from mid-summer through leaf color in the fall. For evergreen plants apply spring through summer.
Remarks A wide variety of deciduous shrubs and some evergreen plants are sensitive to imazapyr. Bigleaf and other maples, hazel, ocean spray, cherries, oaks, cottonwood, willow, poison oak, madrone and chinkapin are sensitive.
Label restricts applications for site preparation to sites that will be planted to certain conifer species and adjusts rates by species. For Douglas-fir and western hemlock rates are 12 to 24 oz/A. Ponderosa pine, lodgepole pine, sugar pine and white pine are limited to 12 to16 oz/A. Since labels can differ users should carefully read product labels for labeled conifer species and maximum rates. Some imazapyr products containing 2 lb ai/gal are available for forest management and are generally used for site preparation at twice the rate as 4 lb ai products. Imazapyr can be a good site preparation tank mix partner with glyphosate and other herbicides on deciduous brush. Add additional surfactant for site preparation as per label. Surfactants may increase injury in conifer release and should be avoided.
Caution Imazapyr has significant soil activity and high rates or overdosing can result in mortality or injury to conifers and non-target plants that have root systems extending into treated areas. Do not apply more than 1.5 lb ae/A per year. Avoid contact with conifer foliage that is actively growing or not dormant for release treatments. For Douglas-fir release risk of injury is reduced by treating after the formation of a firm dormant bud in fall.
Site of action Group 2: acetolactate synthase (ALS) inhibitor
Chemical family Imidazolinone
metsulfuron (Escort XP and others)
Rate 0.6 to 1.2 oz ai/A (1 to 2 oz/A product)
Time Apply for site preparation when brush plants and hardwoods are fully leafed out from summer through the fall. Avoid conifer foliage contact as injury may occur.
Remarks For broadcast site preparation use in Oregon and Washington west of Cascades. Metsulfuron controls a wide variety of deciduous shrubs and herbaceous plants prior to planting. Rubus species such as blackberries, salmonberry, thimbleberry, and blackcap are especially sensitive to metsulfuron and lower rates effectively control these. Other species controlled include snowberry, cottonwood, cherry, willow, oak, and ocean spray. A number of herbaceous weeds are controlled, but bracken fern and sword fern are the major forestry targets. Consult labels for additional weeds controlled. Douglas-fir, Sitka spruce, Western red cedar, western hemlock, ponderosa pine and grand fir can be planted after application. Other species can be planted with prior tolerance experience. Metsulfuron can be added as a tank mix partner to mixes focused on deciduous brush communities. Metsulfuron mixed with sulfometuron (premixed as Oust Extra and others) can be a component in a broad spectrum site preparation application.
Caution Metsulfuron can be damaging to conifers and users should avoid contact with conifer foliage.
Site of action Group 2: acetolactate synthase (ALS) inhibitor
Chemical family Sulfonylurea
triclopyr ester (Garlon 4 Ultra, Garlon 4, Triclopyr 4)
Rate 1 to 1.5 lb ae/A for conifer release (1 to 1.5 qts/A product); 3 to 6 lb ae/A for site preparation (3 to 6 qts/A product)
Time For conifer release apply in the spring before conifers break bud and start to grow or in late summer after conifers have set a dormant bud. For site preparation apply when deciduous brush plants and hardwoods are fully leafed out from summer through the fall. Treat evergreen plants from early spring into summer. Avoid contact with conifer foliage during active growth.
Remarks Triclopyr ester controls a wide variety of deciduous and evergreen shrubs as well as herbaceous plants prior to planting or in established plantations as a broadcast release spray. Species such as blackberries, poison oak, Scotch broom, gorse, snowbrush ceanothus, madrone, tanoak, and myrtle are especially sensitive to triclopyr.
For conifer release treat blackberries in late summer into late fall for best control at lowest rates (1 qt/A product). Scotch broom can be reasonably suppressed in spring at a 1.25 qts/A of product without undue risk of conifer injury. Fall release rates may need to be higher and control may be less. Other evergreen species may need higher release rates. Oil type surfactants may improve control for site preparation but can increase potential for injury on conifers and should be used carefully. Other species controlled include cottonwood, alder, cherry, willow, and oak. A number of broadleaved herbaceous weeds are controlled but these uses are not generally used in the Pacific Northwest on forest sites. Most conifers have good to moderate tolerance to at least the lowest rates for release, but ponderosa pine is extremely sensitive and should not be treated. Consult labels for additional weeds controlled.
Caution Avoid contact with new growing conifer foliage. Ponderosa pine is sensitive at all times and will be injured. Triclopyr ester is volatile and vapors can move off site during warm temperatures and damage conifers or other desirable plants. Products containing triclopyr salts may be used as an alternative to esters and are less volatile with less risk of off-site movement but control of some species may be reduced.
Site of action Group 4 synthetic auxin
Chemical family Pyridine