The United States Department of Agriculture takes herbicide application practices very seriously. You have to have a state pesticide handlers license to apply many of these chemicals or even to purchase them. I have developed this list of chemicals as a general overview of herbicides used to control of woody stemmed pests.
I want to thank Cornell University's Pesticide Management Education Program, the United States Forest Service and the Environmental Protection Administration for information included in this list of herbicides.
1. 2,4-D - "Brush-Rhap"
2,4-D is a chlorinated phenoxy compound that functions as a systemic herbicide and is taken in by the target plant 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. Dioxin is no longer found in the chemical in harmful quantities and considered safe for use under specific labeled conditions. 2,4-D is slightly toxic to wildfowl. Mallards, pheasants, quail, and pigeons and some formulations are highly toxic to fish.
Using 2,4-D as a forestry herbicide is primarily used in site preparation for conifers and as an injected chemical in target tree trunks and stumps.
Commercial names for products containing 2,4-D include but are not limited to Weedtrine-II, Aqua-Kleen, Barrage, Plantgard, Lawn-Keep, Planotox and Malerbane.
2. Amitrole - "Triazole"
Amitrole is a nonselective systemic triazole herbicide and taken in by the target plant as a foliar spray. Not intended for agriculture, the herbicide is used on non-cropland for control of annual grasses and perennial and annual broadleaf weeds, for poison ivy control, and for control of 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 and may be purchased and used only by certified applicators. Products containing amitrole must bear the signal word "Caution". Still, the chemical is considered safe for workers applying the herbicide.
Commercial names for products containing Amitrole include but are not limited to Amerol, Amino Triazole, Amitrol, Amizine, Amizol, Azolan, Azole, Cytrol, Diurol, and Weedazol.
3. Bromacil - "Hyvar"
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 and sprayed or broadcast over the soil. It is especially useful against perennial grasses and available in granular, liquid, water soluble liquid, and wettable powder formulations.
The U. S. Environmental Protection Agency classifies Bromacil as a general use herbicide but requires dry formulations have the word "Caution" printed on packaging and liquid formulations must have word "Warning". Liquid formulations are moderately toxic, while dry formulations are relatively non-toxic and some states restrict its use.
Commercial names for products containing Bromacil include Borea, Bromax 4G, Bromax 4L, Borocil, Rout, Cynogan, Uragan, Isocil, Hyvar X, Hyvar XL, Urox B, Urox HX, Krovar.
4. Dicamba - "Banvel"
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 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.
Commercial names for products containing Dicamba include Banvel, Banex, Brush Buster, Vanquish and Velsicol.
5. Fosamine - "Krenite"
Ammonium salt of fosamine is an organophosphate herbicide used to control woody and leafy plants and 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 and used in a water soluble liquid foliar spray.
The Environmental Protection Agency 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 or small mammals.
Commercial names for products containing fosamine is Krenite and is not registered for use in California and Arizona.
6. Glyphosate - "Roundup"
Glyphosate is usually formulated as an isopropylamine salt but can also be described as an organophosphorus compound. It is one of the most commonly used general herbicides and considered safe to handle. Glyphosate (commonly known as Roundup) 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 coop.
The term "general use" means that glyphosate can be purchased without permit and applied, according to label, in many plant control situations. The term "broad-spectrum" means that the formulation 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.
Commercial names for products containing glyphosate include Roundup (includes surfactant), Cornerstone (no surfactant) and Accord (no surfactant).
7. Hexazinone - "Velpar"
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.
Hezazinone is effective in controlling many woody and herbaceous weeds at application rates tolerated by pines, which means foresters can selectively manage competing vegetation in pine forest understories or 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 (5 and 10-percent active ingredient.
Trade names for products containing hexazinone are DPX 3674 and Velpar. It may be used in combination with other herbicides such as bromacil. The manufacturer is DuPont.
8. Imazapyr - "Arsenal"
Imazapyr is an herbicide that disrupts an enzyme (found only in plants) necessary for protein synthesis. The chemical is absorbed by foliage and by roots of plants which means applying a spray to a leaf where the runoff will continue to work on soil contact. It is a major recommended pesticide for control of many invasive exotic plants and can be used as a foliar spray or applied as a squirt to cut stumps, in a frill, girdle, or using an injection tool.
Forestry applications for this product are increasing and imazapyr is a selective herbicide in pine forests with hardwood competition. Target species for the chemical used in a forestry TSI setting are broadleaved understory species. Imazapyr is effective for creating openings for wildlife use and is most effective when applied as a post-emergent herbicide.
Commercial names for products containing imazapyr are limited to Arsenal products and manufactured by BASF Corporation.
9. Metsulfuron - "Escort"
Metsulfuron is a sulfonylurea compound that is used as a selective pre- and postemergence herbicide - which means it can be effective on many woody stems before and after sprouting. This compound herbicide works as a systemic when applied to target plants through both leaf and soil root action. The chemical works rapidly, particularly when taken up by broadleaf "weeds" and some annual grasses. Agricultural crops and conifers can be planted behind this product when given a chemical break-down period of time which is plant species specific (can be as long as several years).
Forestry application for this product is to control select broadleaf weeds, trees and brush, and 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. Metsulfuron-methyl is the active ingredient in the herbicide products Escort XP and Metsulfuron Methyl 60 DF.
Commercial names for products containing Metsulfuron are Escort and Metsulfuron-methyl and the basic manufacturer is DuPont Agricultural Products.
10. Picloram - "Tordon"
Picloram is a systemic herbicide and plant growth regulator, used for general woody plant control and mostly used in forest applications. 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 must not be applied directly to water. Picloram’s potential to contaminate groundwater and its ability to damage nontarget plants, limit it's use to licensed pesticide applicators. Picloram can stay active in soil for a moderately long time depending on the type of soil, soil moisture and temperature so site assessment is necessary before use. It is relatively non-toxic to humans.
Commercial names for products containing picloram are Tordon K and Tordon 22K formulations, which contain only picloram as an active herbicide ingredient. Other formulated products like Tordon 101 Mixture and Tordon RTU) contain picloram and another herbicide. The manufacturer of picloram is Dow Chemical Company.
11. Triclopyr - "Garlon"
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 a 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 3 months. It is relatively safe and unusually effective on woody plants and is used for foliar applied sprays to woody stem pests in forested areas.Commercial names for products containing picloram are Garlon, Turflon, Access, Redeem, Crossbow, Grazon, ET and manufactured by Dow Agrosciences. The herbicide may be mixed with picloram or with 2,4-D to make it more effective.