Herbicides Used to Control Woody Stem Plants

2,4-D

2,4-D is a chlorinated phenoxy compound that functions as a systemic herbicide when used on target plants as a foliar spray. This chemical compound herbicide is used to control many types of broadleaf weeds, shrubs, and trees. It is particularly important in agriculture, rangeland shrub control, forest management, home and garden situations, and for the control of aquatic vegetation.

Dioxin in the "Agent Orange" formulation (which includes 2,4-D) used in Vietnam is often associated with 2,4-D. However, dioxin is no longer found in the chemical in harmful quantities and is considered safe for use under specific labeled conditions. 2,4-D is slightly toxic to wildfowl. It can be toxic to mallards, pheasants, quail, and pigeons, and some formulations are highly toxic to fish.

As a forestry herbicide, 2,4-D is primarily used in site preparation for conifers and as an injected chemical in target tree trunks and stumps.

Amitrole

Amitrole is a nonselective systemic triazole herbicide used on target plants as a foliar spray. While amitrole is not intended for agriculture, the herbicide is used on non-cropland for control of annual grasses, perennial and annual broadleaf weeds, poison ivy, and aquatic weeds in marshes and drainage ditches.

Because amitrole has been determined potentially unsafe when applied to edible plants, berries, and fruits, the chemical is controlled. Amitrole is classified as a restricted use pesticide (RUP) and may be purchased and used only by certified applicators. Products containing amitrole must bear the signal word "caution." However, this chemical is considered safe for workers applying the herbicide.

Bromacil

Bromacil is one of a group of compounds called substituted uracils. It works by interfering with photosynthesis, the process by which plants use sunlight to produce energy. Bromacil is an herbicide used for brush control on non-cropland areas. It is sprayed or broadcast over the soil. Bromacil is especially useful against perennial grasses. It is available in granular, liquid, water-soluble liquid, and wettable powder formulations.

The U. S. Environmental Protection Agency (EPA) classifies Bromacil as a general use herbicide, but requires dry formulations have the word "caution" printed on the packaging and liquid formulations to have word "warning." Liquid formulations are moderately toxic, while dry formulations are relatively non-toxic. Some states restrict Bromacil's use.

Dicamba

Dicamba is a slightly phenolic crystalline solid used in the control of annual and perennial broadleaf weeds, brush, and vines on non-cropland areas. Non-cropland areas include fence rows, roadways, rights-of-way, maintenance of wildlife openings, and non-selective forest brush control (including site preparation).

Dicamba acts like a naturally-occurring plant hormone and causes uncontrolled growth in plants. The application of this auxin-type herbicide causes abnormal growth that is so severe, the plant dies. In forestry, Dicamba is used for ground or aerial broadcast, soil treatment, basal bark treatment, stump (cut surface) treatment, frill treatment, tree injection, and spot treatment.

Dicamba should generally be applied during periods of active plant growth. Spot and basal bark treatments can be applied when plants are dormant, but should not be done when snow or water prevent application directly to the ground.

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Herbicides Used to Kill Shrubs and Trees

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Fosamine

Ammonium salt of fosamine is an organophosphate herbicide used to control woody and leafy plants. This is a plant growth regulator. This selective, post-emergent (after growth begins) formulation prevents dormant plant tissues from growing. Fosamine is successfully used on target species like maple, birch, alder, blackberry, vine maple, ash, and oak. It is used in a water-soluble liquid foliar spray.

The EPA prohibits fosamine ammonium from being used on croplands or in irrigation systems. It may not be applied directly to water, or areas where surface water is present. Soils treated with this herbicide should not be converted to food/feed croplands within one year of treatment. It has been determined that fosamine is "practically" non-toxic to fish, honey bees, birds, and small mammals.

Glyphosate

Glyphosate is usually formulated as an isopropylamine salt but it can also be described as an organophosphorus compound. It is one of the most commonly used general herbicides and it is considered safe to handle. Glyphosate is a broad-spectrum, non-selective systemic herbicide used in a liquid spray on all target annual and perennial plants. It can be found and purchased in every garden center or feed and seed co-op.

The term "general use" means that glyphosate can be purchased without​ a permit and applied, according to the label, in many plant control situations. The term "broad-spectrum" means that it is effective over most plant and tree species (although overuse may be decreasing this ability). The term "non-selective" means it can control most plants using recommended rates.

Glysophate can be used in many forestry situations. It is applied as a spray foliar application for both conifer and broadleaf site preparation. It is used as a squirt liquid for stump application and for tree injection/frill treatments.

Hexazinone

Hexazinone is a triazine herbicide used to control many annual, biennial, and perennial weeds, as well as some woody plants. It's preferred use in forestry is on non-crop areas that need selective control of weeds and woody plants. Hexazinone is a systemic herbicide that works by inhibiting photosynthesis in the target plants. Rainfall or irrigation water is needed before it becomes activated.

Hexazinone is effective in controlling many woody and herbaceous weeds at application rates tolerated by pines. This means foresters can selectively manage vegetation in pine forest understories or in areas where pines are to be planted. Formulations labeled for forestry use include a water-soluble powder (90 percent active ingredient), a water-mix liquid spray, and free-flowing granules (five and ten percent active ingredient).

Imazapyr

Imazapyr is an herbicide that disrupts an enzyme found only in plants that is necessary for protein synthesis. The chemical is absorbed by foliage and by roots of plants, which means applying a spray to leaves where the runoff will continue to work on soil contact. It is a major recommended pesticide for control of many invasive exotic plants. It can be used as a foliar spray or applied as a squirt to cut stumps, in a frill, girdle, or with an injection tool.

Imazapyr is a selective herbicide in pine forests with hardwood competition. Forestry applications for this product are increasing. In a timber stand improvement (TSI) setting, broadleaved understory plants are the target species for this chemical. Imazapyr is effective for creating openings for wildlife use and is most effective when applied as a post-emergent herbicide.

Metsulfuron

Metsulfuron is a sulfonylurea compound that is used as a selective pre- and postemergence herbicide, which means it can be effective on many woody stem plants before and after sprouting. When applied to target species, this compound systemically attacks plants through the leaves and the roots. The chemical works rapidly. Agricultural crops and conifers can be planted after this product after the chemicals have safely broken down in the soil, which is plant-specific and can take as long as several years.

In forests, this product is used to control select broadleaf weeds, trees, and brush, as well as some annual grasses which compete with crop or beneficial trees. It stops cell division in the shoots and roots of the target plant, causing plants to die.

Picloram

Picloram is a systemic herbicide and plant growth regulator used for general woody plant control in forests. The basic formulation can be applied by broadcast or spot treatment as a foliar (leaf) or soil spray. It can also be used as a basal bark spray treatment.

Picloram is a restricted herbicide, which requires a license to purchase, and it must not be applied directly to water. Picloram’s potential to contaminate groundwater and its ability to damage nontarget plants limit its use to licensed pesticide applicators. Picloram can stay active in the soil for a moderately long time depending on the type of soil, soil moisture, and temperature, so site assessment is necessary before use. Picloram is relatively non-toxic to humans.

Triclopyr

Triclopyr is a selective systemic herbicide used to control woody and herbaceous broadleaf plants in commercial and protected forests. Like glyphosate and picloram, triclopyr controls target weeds by mimicking the plant hormone auxin, thus causing uncontrolled plant growth and ultimate plant death.

It is a non-restricted herbicide but may be mixed with either picloram or with 2,4-D to extend its utility range. The product will either have "danger" or "caution" on the label, depending on the specific formulation (which may or may not be restricted).

Triclopyr breaks down in the soil very effectively, with a half-life of between 30 and 90 days. Triclopyr degrades rapidly in water and only remains active in decaying vegetation for about three months. It is relatively safe and unusually effective on woody plants. It is used in forested areas as foliar sprays.