Commonly Used Herbicides for Directed Foliage Applications

2,4-D ester (Weedone LV 4 or LV 6 and many others)

Rate 1 to 4 % product v/v in water)

Time Apply when broadleaved weeds are small in the spring for best results. For woody plants treat when they are active from spring through summer. Avoid contact with conifers especially when they are actively growing.

Remarks 2,4-D controls a large spectrum of broadleaved weeds and woody plants on forest sites including thistles, false dandelion, woodland groundsel, sow thistle, alder, madrone, manzanita species and many others. Amine salt formulations can also be used, but ester products perform better in early spring and on woody species. For best herbaceous control apply in spring while plants are small. Addition of an oil or seed oil surfactant may improve control on evergreen brush species and some broadleaved weeds.

Caution Consult label to avoid exceeding maximum yearly and single application rate. Esters are volatile and vapors can move off target in hot weather potentially damaging conifers and desirable plants.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid

clopyralid (Transline and others)

Rate 1/4 to 1/2 oz product per gallon of water to treat 1000 sq ft (equivalent to 2/3 to 1 1/3 pints per acre)

Time Apply when plants are actively growing, but especially in the spring when susceptible weeds are present and developing.

Remarks Clopyralid controls a select group of herbaceous plants and elderberry on forest sites. For control of bull thistle and small woodland groundsel, use the lower rate early in the growing season. In late spring higher product rates may be needed to control larger plants. Canada thistle is best controlled at bud stage in late spring. Fall applications can be effective on certain species. Additional sensitive weeds include other thistles, clovers, hawkweeds, yellow starthistle, sow thistles, prickly lettuce, some knapweeds and vetches. Red elderberry is effectively controlled during the summer foliage season. Clopyralid can be an effective tank mix herbicide with 2,4-D for broad spectrum control on mixed broadleaved weeds in reforestation sites. Conifers, grasses and many other broadleaved weeds are tolerant.

Site of action Group 4: synthetic auxin

Chemical family Pyridine

glyphosate (Rodeo, Roundup Custom and many others)

Rate 1 to 5 % product v/v in water

Time Apply as a directed spray on foliage of grasses and annual weeds any time they are green and growing. Perennial weeds like bracken fern and deciduous shrubs should be treated from mid-summer though fall before significant leaf fall. Avoid contact with desirable conifers and non-target plants.

Remarks Glyphosate can control a wide variety of deciduous shrubs such as salmonberry, thimbleberry, hazel, oceanspray, vine maple, cherry, elderberry, poison oak, and perennial forbs like bracken fern as a foliage spray.

There are many glyphosate products labeled for forestry use. Users should carefully read the product label they are using and make sure they do not exceed maximum labeled concentrations. Use the lower rates for grasses and weeds and higher concentrations for woody plants. Products that have no surfactant in the formulation may be safer spraying near conifers in case of accidental overspray, although additional surfactant may improve control.

Caution Douglas-fir and other conifers can be injured by glyphosate because of any overspray during directed spraying. They are most sensitive as buds swell and budbreak occurs in the spring through early summer. Apply around 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, Polaris AC Complete and others)

Rate 0.25 to 5 % product v/v in water.

Time Apply when brush plants and hardwoods are fully leafed out from mid-summer through leaf color in the fall avoiding conifer contact and over application near their roots.

Remarks A wide variety of deciduous shrubs and some evergreen plants are sensitive to imazapyr. Maples, hazel, ocean spray, cherries, oaks, cottonwood, willow, poison oak, madrone and chinkapin are sensitive. Recovering bigleaf maple sprout clumps (one to two years from cutting) are effectively controlled with a 2.5% solution from summer into fall. Applications should be made just to cover foliage but not to runoff. Although imazapyr has activity on many grasses and forbs, it is rarely used for those species in forestry in the Northwest.

Some product labels restrict applications for site preparation to sites that will be planted to certain conifer species (Douglas-fir, western hemlock, ponderosa pine, lodgepole pine, sugar pine and white pine) or around certain established conifers (Douglas-fir, lodgepole pine, white pine) for release. Users should carefully read product labels for labeled sites, conifer species and any maximum per acre rates. Some products containing 2 lb ai/gal are available for forest management and are generally used at twice the rate as 4 lb ai products.

Caution Imazapyr has significant soil activity and high rates or over application 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 per acre per year. Avoid contact with conifer foliage.

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

Chemical family Imidazolinone

metsulfuron (Escort XP, Patriot and others)

Rate 2 to 4 ounces product per 100 gallons of water.

Time Apply when brush plants and hardwoods are fully leafed out from summer through the fall but before leaf coloration. Avoid conifer foliage contact.

Remarks Metsulfuron controls a wide variety of deciduous shrubs and herbaceous plants prior to planting or in established plantations as a directed spray. 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 oceanspray. A number of herbaceous weeds are controlled, but bracken fern and sword fern are the major forestry targets. Consult labels for additional weeds controlled.

Caution Metsulfuron can be damaging to conifers and users should avoid contact with conifer foliage if they are present.

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

Chemical family Sulfonylurea

triclopyr ester (Garlon 4 Ultra, Garlon 4, Triclopyr 4)

Rate 1 to 5% product v/v in water.

Time Apply when deciduous brush plants and hardwoods are fully leafed out from summer through the fall but before leaf coloration. Treat evergreen plants from spring into summer. Avoid contact with conifer foliage especially 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 directed spray. Species such as blackberries, poison oak, Scotch broom, gorse, snowbrush ceanothus, madrone, tanoak, and myrtle are especially sensitive to triclopyr. For blackberries treat in late summer into late fall for best control at lowest rates (1%). Scotch broom, gorse and many evergreen brush species can be effectively controlled from spring and early summer applications at a 2% concentration along with oil type surfactants. 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 Northwest on forest sites. Consult labels for additional weeds controlled.

Caution Avoid contact with conifer foliage, especially ponderosa pine. Triclopyr ester is volatile and vapors can move off site during warm temperatures and damage conifers or other desirable plants. Products containing triclopyr salts are less volatile and have less risk of off-site movement but control of some species may be reduced.

Site of action Group 4 synthetic auxin

Chemical family Pyridine