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Forest floor

Weed-control chemicals are used in forestry for site preparation before planting, herbaceous weed control during the first 2 years after planting, and release of established crop trees from competing woody vegetation. The purpose of this publication is to provide one-page summaries of the most important characteristics of weed control chemicals used in forestry. These summaries should be used for general reference, not as prescriptions or application guides. Applicators must carefully read the product label before using any pesticide and must follow all directions, precautions, and restrictions.

The herbicides are listed in alphabetical order by their common names. For example, the formulation widely known as Roundup is listed under the common name of its principal active ingredient, glyphosate. While common names are sometimes not as well known as trade names, it is the active ingredient that has the greatest influence on the behavior and properties of the product. Organizing by common names eliminates repetition. To assist in finding information when only the trade name is known, table 1 lists a trade name with the corresponding common name of the active ingredient.

Information Categories

The following information categories are presented for each chemical:

Activity. Herbicides are either foliar active, soil active, or both. this refers to the principal pathway the chemical enters the plant. Foliar-active chemicals must usually have adequate leaf surface area in order to be absorbed by the plant, although in some cases, such as when applied in an oil-based carrier, foliar-active chemicals can be applied directly to the stem. soil- active chemicals are pulled into the plant through the roots as they take up water and transpire.

Movement in Plants. Chemicals are translocated in the food transport system of the plant (the phloem) or in the water transport system (the xylem) or in both. Chemicals transported in the xylem are characteristically soil-active and move with the transpiration flow—from the base of the tree toward the tips of branches and leaves. Chemicals transported in the phloem move both up and down the plant.

Mode of Action. A general statement is provided as to how the chemical affects plant biochemistry.

Selectivity. Types or classes of plants that are generally considered tolerant to the effects of the chemical are presented.

Environmental Considerations. Information is provided on four key characteristics related to the environment:

Volatility—refers to a chemical’s tendency to go from a liquid to a gas after application.

Photodecomposition—indicates whether a chemical is broken down or decomposed by sunlight.

Mobility in Soil—Provides the potential for off-site movement through leaching.

Half-life—indicates the expected time after application that one-half of the chemical would naturally decompose in the environment. For example, suppose that an application is made
of 2 pounds of an active ingredient with a half-life of 30 days. One month after application, 1 pound of the chemical would have decomposed and 1 pound would still be present.

Toxicity. LD50 is the lethal dose of a chemical required to kill 50 percent of a test-animal (rat) population. it is expressed in milligrams of chemical for each kilogram of test-animal weight.

For reasons of comparison, the following toxicities are provided:

Nicotine LD50 = 50 mg/kg (high toxicity)

Caffeine LD50 = 192 mg/kg (moderate toxicity)

Table salt LD50 = 3,000 mg/kg (low toxicity)

Note that for the LD50 measure of toxicity, the lower the number the more toxic the compound.

Product Formulation. Active ingredients are often sold under one or more formulations. this section provides the percentage of the active ingredient and indicates whether it is an amine (water soluble) or ester (oil soluble) liquid or a dry formulation. trade names and manufacturers are also given.

This section provides only the more common formulations and in no way lists all the commercially available products for all active ingredients.

Additional Sources of Information

  • CDMS agro-chemical database: www.cdms.net
  • National Pesticide Information Center: www.npic.orst.edu/npicfact.htm
  • Crop Protection Handbook. vol. 97. Willoughby, OH: meister media Worldwide, 2011.
  • Herbicide Handbook. 10th ed. Champaign, il: Weed science society of America, 2014.

Table 1. Weed Control Products Used in Forestry

ProductActive Ingredient
Aatrexatrazine
Accordglyphosate
Arsenalimazapyr
Banveldicamba
Chopperimazapyr 
2,4-D2,4-D
Escortmetsulfuron 
Garlontriclopyr
Krenitefosamine
Milestoneaminopyralid
Oustsulfometuron
Roundupglyphosate
Tordon picloram
Translineclopyralid
Vanquishdicamba
Velpar hexazinone
Weedone2,4-D

aminopyralid

ActivityFoliar and soil active
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionGrowth regulator
SelectivityPasture grasses and small-grains tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionRapid in water, stable on soil
Mobility in soilLow
Half-life34 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

2.22 percent aminopyralid
Milestone VM Plus (Dow AgroSciences)

atrazine

ActivityPrimarily soil, some foliar activity
Movement in plantsTranslocated in the xylem
Mode of actionPhotosynthesis inhibitor
SelectivityBroad-spectrum broadleaf and grass control; minimally effective on established weeds; used as a preemergent or early postemergent
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilHighly water-soluble but readily adsorbed by organic matter and clay; potential for leaching on sandy soils
Half-life60 days
ToxicityLD50 - 3,080 mg/kg (low toxicity)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

43 percent atrazine
Aatrex 4L (syngenta)

Water-dispersible granule

88 percent atrazine
Aatrex Nine-O (syngenta)

clopyralid

ActivityMostly foliar but is absorbed by roots
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionGrowth regulator
SelectivityHighly effective against many legumesGrasses generally tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilModerate
Half-life14–56 days, typically around 40 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

41 percent clopyralid
Transline (Dow AgroSciences)

2,4-D

ActivityFoliar
Movement in plantsTranslocated in both xylem and phloem
Mode of actionGrowth regulator
SelectivityGrasses generally tolerant
Environmental Considerations
VolatilityRelated to formulation; volatility can be a problem with ester formulations
PhotodecompositionNegligible
Mobility in soilRapid degradation and plant uptake minimizes mobility; leaching potential in sandy soils
Half-life10 days
ToxicityLD50 - 639 mg/kg – 1,646 mg/kg (low toxicity)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

40 percent 2,4-D
Hi-Dep Broadleaf Herbicide (Gordon’s Agricultural Products)

Water-soluble liquid

21 percent 2,4-D amine plus 5 percent picloram
Pathway (Dow AgroSciences) Tordon RTU (Dow AgroSciences)

Water-soluble liquid

40 percent 2,4-D plus 10 percent picloram
Todon 101 Mixture (Dow AgroSciences)

Forms an emulsion when mixed with water

63 percent 2,4-D ester
Weedone LV4 (Nufarm)

Forms an emulsion when mixed with water; soluble in petroleum distilates

87 percent 2,4-D ester
Weedone 650 (Nufarm)

dicamba

ActivityFoliar and soil
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionGrowth regulator
SelectivityGrasses generally tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilRelatively mobile in soil, but degrades rapidly
Half-life14 days
ToxicityLD50 - 1,707 mg/kg (low toxicity)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

40 percent dicamba
Banvel (Arysta LifeScience)

Water-soluble liquid

13 percent dicamba plus 25 percent 2,4-D amine
Banvel 720 (Arysta LifeScience)

Ready-to-use water-based liquid

13 percent dicamba
Banvel CST (Arysta LifeScience)

fosamine

ActivityFoliar
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionGrowth regulator; stops bud development
SelectivityLabeled for broad-spectrum woody plant control
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilNegligible
Half-life8 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

42 percent fosamine
Krenite S (Albaugh Inc.)

glyphosate

ActivityFoliar
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionInhibits the synthesis of specific amino acids
SelectivityNonselective
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilTightly bound to soil and organic matter
Half-life47 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

41 percent glyphosate
Roundup Pro (Monsanto)

Water-soluble liquid

50 percent glyphosate
Roundup Pro Concentrate (Monsanto)

Water-soluble liquid

54 percent glyphosate, plus surfactant
Accord XRT (Dow AgroSciences)

Water-soluble liquid

54 percent glyphosate, no surfactant
Accord Concentrate (Dow AgroSciences)

Water-soluble liquid

52 percent glyphosate
Refuge (Sygenta)

hexazinone

ActivityPrimarily soil-active; some foliar activity
Movement in plantsTranslocated in the xylem
Mode of actionInhibits photosynthesis
SelectivityBroad-spectrum control with some conifer tolerance
Environmental Considerations
VolatilityNegligible
PhotodecompositionSlow; reported to be 10 percent per week
Mobility in soilAdsorbed by organic matter and clay; highly water-soluble with potential for leaching on sandy soils
Half-life90 days
ToxicityLD50 - 1,690 mg/kg (low toxicity)
Product FormulationsTrade Name and Manufacturer

Water-dispersible liquid

25 percent hexazinone
Velpar L (Dupont)

Dispersible granules

63 percent hexazinone plus 12 percent sulfometuron
Oustar (Dupont)

Dry flowable

75 percent hexazinone
Velpar DF (Dupont)

imazapyr

ActivityFoliar and soil
Movement in plantsTranslocated in the xylem and phloem
Mode of actionInhibits the synthesis of specific amino acids
SelectivityConifers generally tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionSignificant in water, slow on soils
Mobility in soilAdsorbed by soil particles; leaching usually not a problem
Half-life27 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationsTrade Name and Manufacturer

Water-soluble liquid

53 percent imazapyr
Arsenal Applicators Concentrate (BASF)

Oil- or water-soluble liquid

28 percent imazapyr
Chopper (BASF)

Water-soluble liquid

27 percent imazapy
Chopper Gen2 (BASF)

Dispersible granules

63 percent imazapyr plus 10 percent mesulfuron
Lineage Clearstand (Dupont)

metsulfuron

ActivityFoliar and soil
Movement in plantsTranslocates in both the xylem and phloem
Mode of actionInhibits the synthesis of specific amino acids
SelectivityBroad-spectrum herbicide with some conifer tolerance
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilLow adsorption to clay but some adsorption to organic matter; solubility increases with increasing pH; some leaching potential but use rates very low
Half-life30 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Dry flowable

60 percent metsulfuron methyl
Escort XP (Dupont)

Dispersible granules

10 percent metsulfuron plus 63 percent imazapyr
Lineage Clearstand (Dupont)

picloram

ActivitySoil and foliar
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionGrowth regulator
SelectivityBroad-spectrum herbicide although most grasses tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionReported to photodecompose but actual rates not conclusively measured
Mobility in soilVery mobile in soil
Half-life90 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

24 percent picloram
Tordon K (Dow AgroSciences)

Water-soluble liquid

10 percent picloram plus 40 percent 2,4-D
Tordon 101 Mixture (Dow AgroSciences)

Water-soluble liquid, ready to use

5 percent picloram plus 21 percent 2,4-D
Tordon RTU (Dow AgroSciences)

Ready-to-use liquid

5 percent picloram plus 21 percent 2,4-D
Pathway (Dow AgroSciences)

Water-soluble liquid

24 percent picloram
Tordon 22K (Dow AgroSciences)

sulfometuron

ActivitySoil and foliar
Movement in plantsTranslocates in both the xylem and phloem
Mode of actionInhibits the synthesis of specific amino acids
SelectivityConifers and other woody perennials tolerant
Environmental Considerations
VolatilityNegligible
PhotodecompositionNegligible
Mobility in soilMobility increases with higher pH; adsorbed by soil organic matter
Half-life20–28 days
ToxicityLD50 - >5,000 mg/kg (practically nontoxic)
Product FormulationTrade Name and Manufacturer

Water-dispersible granule

75 percent sulfometuron
Oust (Dupont)

Water-dispersible granule

12 percent sulfometuron plus 63 percent hexazinone
Oustar (Dupont)

triclopyr

ActivityFoliar
Movement in plantsTranslocated in both the xylem and phloem
Mode of actionNot known exactly but similar to 2,4-D and picloram
SelectivityMost grasses tolerant
Environmental Considerations
VolatilityCan be a problem with ester formulations
PhotodecompositionRapid
Mobility in soilNot readily leached
Half-life30 days
ToxicityLD50 - 713 mg/kg (low toxicity)
Product FormulationTrade Name and Manufacturer

Water-soluble liquid

44 percent triclopyr amine
Garlon 3A (Dow AgroSciences)

Water- and oil-soluble liquid

62 percent triclopyr ester
Garlon 4 (Dow AgroSciences)

Water- and oil-soluble liquid

84 percent triclopyr
Forestry Garlon XRT (Dow AgroSciences)

Ready-to-use liquid

14 percent triclopyr
Pathfinder II (Dow AgroSciences)

PDF Version of ANR-0629.REV

More Information

For more information visit Alabama Forestry, Wildlife & Natural Resources Extension online or contact your county Extension office.

The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency and the Alabama Department of Agriculture and Industries. If a registration is changed or cancelled, the rate listed here is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information.

Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.

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