ANR-629, Reprinted Oct 1996. Ken McNabb, Extension Forester, Associate Professor, Forestry, Auburn University

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Forestry Herbicide Facts

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. Also, organizing by common names eliminates repetition.

To assist you in finding information when you know only the trade name, Table 1 lists the trade name with the corresponding common name of the active ingredient. Included are links to the summaries given in this publication.

Information Categories

The following information categories are presented for each chemical:

Activity. Herbicides are either foliar active, soil active, or both. This refers to how the chemical enters the plant. Foliar-active chemicals must usually have adequate leaf surface area in order to be absorbed by the plant, but in some cases 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 brief description is given of how the chemical affects plant biochemistry.

Selectivity. General classes of plants which are resistant to the effects of the chemical are presented in this section.

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

Volatility--Refers to a chemical's tendency to go into a gaseous state after application.

Photo decomposition--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. Toxicity is provided in reference to mammals and to fish. 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:

Caffeine LD50 = 200 mg/kg (extremely toxic)

Aspirin LD50 = 1,240 mg/kg (moderately toxic)

Table salt LD50 = 3,000 mg/kg (moderately toxic)

LC50 is the lethal concentration in water at which a chemical becomes lethal to 50 percent of a test population of fish.

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.

 Table 1. Weed Control Products Used in Forestry

Product	Active Ingredient
Aatrex 4L	atrazine
Aatrex 80W	atrazine
Aatrex Nine-O	atrazine
Access	picloram &  triclopyr
Accord	glyphosate
Arsenal Applicators Concentrate	imazapyr
Atrazine 4L	atrazine
Banvel	dicamba
Banvel 720	2,4-D &  dicamba
Banvel CST	dicamba
Chopper	imazapyr
Escort	metsulfuron
Fusilade 2000	fluazifop
Garlon 3A	triclopyr
Garlon 4	triclopyr
Oust	sulfometuron
Poast	sethoxydim
Pronone MG	hexazinone
Pronone 10G	hexazinone
Pronone 25G	hexazinone
Pronone Power Pellet	hexazinone
Roundup	glyphosate
Tordon K	picloram
Tordon 101M	2,4-D &  picloram
Tordon 101R	2,4-D &  picloram
Tordon RTU	2,4-D &  picloram
Velpar L	hexazinone
Velpar ULW	hexazinone
Weedone 2,4-DP	dichlorprop
Weedone 170	dichlorprop

Atrazine

Activity	Primarily soil, some foliar activity
Movement in plants	Translocated in water transport system
Mode of action	Photosynthesis inhibitor
Selectivity	Broad spectrum broadleaf and grass control; minimally effective on established weeds; used as a preemergent or early postemergent
Environmental Considerations
Volatility	Negligible
Photodecomposition	Negligible
Mobility in soil	Highly water-soluble but readily adsorbed by organic matter and clay; potential for leaching on sandy soils
Half-life	Specific number not available; relatively long-lived
Toxicity	LD50 - 3,080 mg/kg (moderately toxic) LC50 - slightly toxic
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 43 percent atrazine	Atrazine 4L (Dupont) Aatrex 4L (Ciba Geigy)
Wettable powder 80 percent atrazine	Aatrex 80W (Ciba Geigy)
Water-dispersible granules 90 percent atrazine	Aatrex Nine-O (Ciba-Geigy)

2,4-D and 2,4-DP (Dichlorprop)
Activity	Foliar
Movement in plants	Translocated in the food transport system
Mode of action	Accelerated but disorganized growth
Selectivity	Grasses generally resistant
Environmental Considerations
Volatility	Related to formulation; volatility can be a problem with ester formulations, particularly dichlorprop
Photodecomposition	Minimal
Mobility in soil	Not tightly bound to soil, particularly at higher pH levels; leaching potential in sandy soils
Half-life	28 days
Toxicity	LD50 - 375 mg/kg (moderately toxic) LC50 - 100 ppm (slightly toxic)
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 40 percent 2,4-D amine plus 10 percent picloram	Tordon 101M (Dow/Elanco)
Water-soluble liquid 21 percent 2,4-D amine plus 5 percent picloram	Tordon 101R and Tordon RTU (Dow/Elanco)
Water-soluble liquid 25 percent 2,4-D amine plus 13 percent dicamba	Banvel 720 (Sandoz)
Oil- and water-soluble liquid 30 percent 2,4-D plus 30 percent diclorprop	Weedone 170 (Rhone Poulenc)
Oil- and water-soluble liquid 59 percent diclorprop ester	Weedone 2,4-DP (Rhone Poulenc)

Dicamba
Activity	Foliar and soil
Movement in plants	Translocated in food and water systems
Mode of action	Accelerated but disorganized growth
Selectivity	Grasses generally resistant
Environmental Considerations
Volatility	Minimal
Photodecomposition	Some, but insignificant
Mobility in soil	Relatively mobile in soil
Half-life	14 days
Toxicity	LD50 - 1,707 mg/kg (moderately toxic) LC50 - 35 ppm (slightly toxic)
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 40 percent dicamba	Banvel (Sandoz)
Water-soluble liquid 13 percent dicamba plus 25 percent 2,4-D amine	Banvel 720 (Sandoz)
Ready-to-use water-based liquid 13 percent dicamba	Banvel CST (Sandoz)

Fluazifop
Activity	Foliar
Movement in plants	Translocated in food and water systems
Mode of action	Cell membrane disruption
Selectivity	Grass herbicide; broadleaf and woody plants highly resistant
Environmental Considerations
Volatility	Minimal
Photodecomposition	Minimal
Mobility in soil	Low mobility in soil
Half-life	21 days
Toxicity	LD50 - 4,096 mg/kg (moderately toxic) LC50 - 5.4 ppm (moderately toxic)
Product Formulation	Trade Name and Manufacturer
Oil- and water-soluble liquid 13 percent fluazifop-p-butyl	Fusilade 2000 (ICI Americas)

Glyphosate
Activity	Foliar
Movement in plants	Translocated in food and water systems
Mode of action	Amino acid inhibitor
Selectivity	Non-selective
Environmental Considerations
Volatility	Negligible
Photodecomposition	Negligible
Mobility in soil	Tightly bound to soil and organic matter
Half-life	61 days
Toxicity	LD50 - 5,600 mg/kg (slightly toxic) LC50 - 86 ppm (slightly toxic)
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 41 percent glyphosate plus surfactant	Roundup (Monsanto)
Water-soluble liquid 41 percent glyphosate, no surfactant	Accord (Monsanto)

Hexazinone
Activity	Primarily soil-active; some foliar activity
Movement in plants	Translocated in the water transport system
Mode of action	Inhibits photosynthesis
Selectivity	Broad spectrum control with some selectivity for conifers
Environmental Considerations
Volatility	Minimal
Photodecomposition	Slow; reported to be 10 percent per week
Mobility in soil	Adsorbed by organic matter and clay; highly water-soluble with potential for leaching on sandy soils
Half-life	30 days
Toxicity	LD50 - 1,690 mg/kg (moderately toxic) LC50 - 274 ppm (practically non-toxic) other - eye irritant
Product Formulations	Trade Name and Manufacturer
Water-dispersable liquid 25 percent hexazinone	Velpar L (Dupont)
Granular 75 percent water-soluble 10 percent clay granule 10 percent clay granule 25 percent water-soluble tablet 75 percent water-soluble tablet	Velpar ULW (Dupont) Pronone MG (Proserve) Pronone 10G (Proserve) Pronone 25G (Proserve) Pronone Power Pellet (Proserve)

Imazapyr
Activity	Foliar and soil
Movement in plants	Translocated in food and water systems
Mode of action	Inhibits the synthesis of specific amino acids
Selectivity	Conifers generally resistant
Environmental Considerations
Volatility	Negligible
Photodecomposition	Can be significant
Mobility in soil	Adsorbed by soil; leaching usually not a problem
Half-life	27 days
Toxicity	LD50 - 5,000 mg/kg (slightly toxic) LC50 - 100 ppm (slightly toxic)
Product Formulations	Trade Name and Manufacturer
Water-soluble liquid 54 percent imazapyr	Arsenal Applicators Concentrate (American Cyanamid)
Oil- or water-soluble liquid 3.6 percent imazapyr	Chopper (American Cyanamid)

Metsulfuron
Activity	Foliar and soil
Movement in plants	Translocates in the food and water systems
Mode of action	Inhibits cell division and amino acid synthesis
Selectivity	Broad spectrum herbicide; some apparent conifer selectivity
Environmental Considerations
Volatility	Negligible
Photodecomposition	Negligible
Mobility in soil	Low adsorption to clay but some adsorption to organic matter; solubility increases with increasing pH; some leaching potential but use rates very low
Half-life	42 days
Toxicity	LD50 - 5,000 mg/kg (slightly toxic) LC50 - 150 ppm (practically non-toxic)
Product Formulation	Trade Name and Manufacturer
Dry flowable 60 percent metsulfuron methyl	Escort (Dupont)

Picloram
Activity	Soil and foliar
Movement in plants	Translocated in food and water systems
Mode of action	Accelerated but disorganized growth
Selectivity	Broad-spectrum herbicide although most grasses resistant
Environmental Considerations
Volatility	Minimal
Photodecomposition	Reported to photodecompose but actual rates not conclusively measured
Mobility in soil	Some adsorption but generally very mobile in soil
Half-life	63 days
Toxicity	LD50 - 8,200 mg/kg (slightly toxic) LC50 - slightly toxic
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 24 percent picloram	Tordon K (Dow/Elanco)
Water-soluble liquid 10 percent picloram plus 40 percent 2,4-D amine	Tordon 101M (Dow/Elanco)
Water-soluble liquid, ready to use 5 percent picloram plus 21 percent 2,4-D amine	Tordon 101R (Dow/ELanco) Tordon RTU (Dow/Elanco)
Water- and oil-soluble liquid 17.0 percent picloram plus 32.5 percent triclopyr	Access (Dow/Elanco)

Sethoxydim
Activity	Foliar
Movement in plants	Translocated in the food transport system
Mode of action	Inhibits cell membrane synthesis
Selectivity	Grass herbicide; broadleaf and woody plants resistant
Environmental Considerations
Volatility	Minimal
Photodecomposition	Can be significant
Mobility in soil	Readily adsorbed by organic matter; low soil mobility
Half-life	11 days
Toxicity	LD50 - 2,676 mg/kg (moderately toxic) LC50 - slightly toxic Other - eye irritant
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 18 percent sethoxydim	Poast (BASF)

Sulfometuron
Activity	Soil and foliar
Movement in plants	Translocates in the food and water systems
Mode of action	Stops cell division, particularly at growing tips
Selectivity	Conifers and other woody perennials resistant
Environmental Considerations
Volatility	Minimal
Photodecomposition	Minimal
Mobility in soil	Mobility increases with higher pH; adsorbed by soil organic matter
Half-life	10 days
Toxicity	LD50 - 5,000 mg/kg (slightly toxic) LC50 - 12.5 ppm (slightly toxic)
Product Formulation	Trade Name and Manufacturer
Water-dispersable granule 75 percent sulfometuron-methyl	Oust (Dupont)

Triclopyr
Activity	Foliar
Movement in plants	Translocated in the water and food systems
Mode of action	Not known exactly, but similar to 2,4-D and picloram
Selectivity	Most grasses tolerant
Environmental Considerations
Volatility	Can be a problem with ester formulations
Photodecomposition	Rapid
Mobility in soil	Not readily leached
Half-life	46 days
Toxicity	LD50 - 713 mg/kg (moderately toxic) LC50 - 117 ppm (practically non-toxic)
Product Formulation	Trade Name and Manufacturer
Water-soluble liquid 44 percent triclopyr amine	Garlon 3A (Dow/Elanco)
Water- and oil-soluble liquid 62 percent triclopyr ester	Garlon 4 (Dow/Elanco)
Water- and oil-soluble liquid 32.5 percent triclopyr ester and 17.0 percent picloram ester	Access (Dow/Elanco)

Additional Sources of Information

Weed Science Society of America. 1989. Herbicide Handbook (6th edition) published by the Weed Science Society of America, Champaign, Illinois.

Miller, J.H. and R.J. Mitchell. 1988. A Manual on Ground Applications of Forestry Herbicides. U.S. Forest Service, Atlanta, Georgia. Management Bulletin R8-MB 21.