SAFETY AND ENVIRONMENTAL CONSIDERATIONS FOR THE USE OF HERBICIDES TO CONTROL INVASIVE PLANTS
The most important consideration when using any pesticide (the term pesticide is generic and includes herbicides, insecticides, fungicides, etc.) is to read the label first! Although this may seem obvious, it is still of primary importance. Pesticide use in this country is in fact regulated by label language, thus it is a violation of state and federal law to use a pesticide product contrary to label directions. Specific statements on pesticide labels give precautions to be followed. For example, all pesticides not designed for aquatic use will carry the statement: "Do not apply directly to water or to areas below the high tide mark." Pesticides toxic to fish may require a setback from fish-bearing waters, and will include statements that the product is highly toxic to fish. Pesticides that are highly toxic and/or environmentally damaging will be classified as Restricted Use Pesticides, meaning that one needs to be state certified in order to purchase and use these products. In Connecticut all aquatic use of pesticides requires a site-specific permit, issued by the Department of Environmental Protection (DEP).

All pesticide labels have a signal word on them. The signal word is an indicator of the potential human toxicity of the product. The three signal words, in order from highest to lowest toxicity, are: Danger, Warning and Caution. The areas of toxicity to which the signal word applies are acute (single dose) oral, dermal, and inhalation toxicity; also skin irritation and eye irritation. The label will explain the area of toxicity to which the signal word pertains, although it sometimes takes careful reading to understand. The signal word applies to the material in the container, not diluted product. When concentrates are diluted (usually with water) the toxicity will decrease proportionately. Dilution with oil may make the chemical more easily absorbed through the skin, thus any reduction in toxicity may not be in proportion to the dilution.

The herbicides most commonly used for control of invasive plants are glyphosate (active ingredient in Roundup, Accord, and Rodeo), and triclopyr (active ingredient in Ortho Brush-B-Gon, Garlon, and Crossbow, which is triclopyr combined with 2,4-D). Glyphosate and triclopyr have different chemical properties and represent different hazards. Again, the specific protective clothing to be worn, and health hazards of the product will be noted on the product label. Because formulations change, as do the types of protective clothing available, no attempt to specify such will be made here.
Glyphosate has low oral toxicity (acute or chronic) to humans or other animals. Some formulations are irritating to skin or eyes, so precautions to avoid contact should be followed. Glyphosate does not persist or bioaccumulate in the environment. The most significant environmental impact resulting from glyphosate use is modification of habitat due to vegetation killed (of course, this is the effect desired when attempting to control invasive plants).
The oral toxicity of triclopyr is fairly low relative to other pesticides, but not as low as that of glyphosate. Take precautions to avoid exposure. Amine-based triclopyr formulations are corrosive and damaging to eyes and skin, thus they must be handled with a great deal of care. Follow the label directions for protective eyewear and clothing. Toxicity to birds and fish is relatively low, although ester formulations are more toxic to fish than amine formulations or the parent acid of triclopyr.

To optimize herbicidal efficacy, and to avoid injury to yourself, non-target plants and the environment… ALWAYS READ AND FOLLOW THE DIRECTIONS ON THE PRODUCT LABEL!

All herbicides mentioned in this guide are classified as "General Use" products. "Homeowner" products can be purchased over the counter in garden centers, whereas products packaged in larger containers or in more concentrated forms may only be available at agricultural chemical dealerships. In order to purchase or use a "Restricted Use" pesticide, one must obtain certification as a Commercial Pesticide Applicator, which requires passing an exam administered by Connecticut DEP. Also, DEP approval must be obtained prior to application of any pesticide to a body of water.

For control of perennial invasive plants (especially trees, shrubs and woody vines):

Cutting, mowing or using a contact (non-systemic) herbicide will usually not kill well-established (deep-rooted) plants. Regrowth will occur from stumps, underground rootstocks or creeping underground stems (rhizomes). Cutting alone often results in a greater number of sprouts or excessive branching. Non-chemical control of well-established, deep-rooted plants will require either digging up the entire root system or repeatedly cutting the top growth over several years.

 

Use of a systemic herbicide is often necessary to achieve adequate control of such troublesome invasive plants. Systemic herbicides absorb into the plant foliage and/or stems, then translocate (move) and accumulate to toxic levels in the growing points or roots. Following foliar applications in late summer or fall (prior to leaf color change), systemic herbicides will accumulate in storage tissues below ground. In this way, the herbicide is more likely to prevent regrowth the following year.

 

Herbicides may be applied by the following methods to control invasive plants:

1. Postemergence (Foliar) Applications -
   a. Spray properly diluted herbicide (in water) onto plant foliage.
   b. Wipe herbicide (more concentrated form) onto leaves with wiper applicator.
2. Cut Stump Treatments - Paint concentrated form of herbicide on freshly cut stumps of woody plants.
3. Basal Bark Treatments – Herbicide mixed into oil or diesel fuel carrier to penetrate through bark. Often used for dormant season treatments.
4. Application equipment – hand-held sprayers, backpack sprayers, paint brush or sprayer for stump and bark treatments
5. Addition of a non-ionic surfactant [@ 0.5 fluid ounce (1 tablespoon) per gallon of spray] will improve coverage of spray droplets on treated leaves and enhance absorption of the herbicide into the plant. Surfactants (sold under many trade names) can be purchased at fertilizer and pesticide dealerships. Some herbicide formulations already contain a surfactant – check the product label carefully.

 

Herbicides commonly used for invasive plant control:

Glyphosate
Active Ingredient (a.i.): N-(phosphonomethyl)glycine, as the isopropylamine salt

Brand-name Products (All product labels contain signal word of CAUTION):
Roundup Ready-to-Use Spray 0.96% a.i.
Roundup Concentrate 18% a.i.
Roundup Super Concentrate 41% a.i.
Roundup Pro, Roundup Ultra 41% a.i.
accord, Glyfos 41% a.i.
Rodeo 53.8% a.i.

Glyphosate is a broad-spectrum herbicide that is absorbed by plant leaves and is systemic (translocated) within the plant. Nearly all herbaceous plants and most woody plants are susceptible to glyphosate, which inhibits synthesis of three amino acids necessary for plant growth. Glyphosate is a rather slow-acting herbicide; symptoms appearing within a week include chlorosis (yellowing) and stunting of the youngest leaves and growing point. It may take more than 2 weeks for the plant to die. Injury symptoms and death occur more rapidly in young, actively growing plants and when temperatures are warm. Woody plants are more susceptible to glyphosate when treated in late summer or fall. Damage may not be apparent until the following spring as leaves either fail to emerge from buds or are dwarfed, misshapen, and yellow.

Glyphosate does not exhibit herbicidal activity in the soil. It is bound rapidly and tightly to soil particles (organic matter and clay), and therefore is not taken up by plant roots and does not affect seed germination. Although it is not absorbed by roots or through intact bark, it can cause damage if sprayed on exposed roots, or on bark that is very thin, green or cracked. Glyphosate is readily biodegraded by microorganisms, thus it does not persist in soil or water. When used properly, glyphosate poses minimal risk to human health or to the environment.

Both ROUNDUP PRO and ROUNDUP ULTRA contain a surfactant that enhances glyphosate absorption into treated leaves. If using a glyphosate formulation other than these two, addition of a non-ionic surfactant (0.5 fl. oz. per gallon) to the spray tank will increase the herbicidal activity of glyphosate.

For control of emergent or floating aquatic plants or plants growing along a shoreline (where spray will contact the water), the RODEO formulation of glyphosate should be used. RODEO does not contain surfactants included in ROUNDUP products. Prior to applying any pesticide to a body of water or to plants in a wetland, one must obtain a permit from DEP. The half-life of glyphosate in water is approximately 2 weeks, but it does not significantly affect submerged plants. Glyphosate toxicity to fish and other aquatic organisms is very low.

 

Triclopyr
Brand-name Products:
Active Ingredient (a.i.): 3,5,6-trichloro-2-pyridinyloxyacetic acid, as the triethylamine salt
Brush-B-Gon Poison Ivy, Poison Oak & Brush Killer2 (Ready-to-Use Spray) 0.7% a.i.
Brush-B-Gon Poison Ivy, Poison Oak & Brush Killer1 (Concentrate) 8.0% a.i.
(Both have signal word: CAUTION)
Garlon 3A 44.4% a.i. (Signal word: DANGER)
Active Ingredient (a.i.): 3,5,6-trichloro-2-pyridinyloxyacetic acid, butoxyethyl ester
Pathfinder II 13.6% a.i. (Signal word: CAUTION)
Garlon 4 61.6% a.i. (Signal word: CAUTION)
Crossbow: 2,4-D + Triclopyr (low volatile ester formulation) (Signal word: CAUTION)
Active Ingredients:
2,4-dichlorophenoxyacetic acid, butoxyethyl ester: 34.4%
3,5,6-trichloro-2-pyridinyloxyacetic acid, butoxyethyl ester: 16.5%
CROSSBOW is registered for use in pastures.

Triclopyr is a systemic herbicide that controls most broadleaf plants (herbaceous and woody) but not grasses or sedges at normal use rates. It is especially useful in brush control and for use on freshly cut stumps to prevent re-sprouting.

Triclopyr interferes with normal expansion and division of plant cells, resulting in distorted growth (cupped leaves, twisted stems, plugged vascular tissues). The herbicidal activity of triclopyr is more rapid than that of glyphosate. Herbaceous plants sprayed with triclopyr may show injury symptoms within 24 hours and usually die in a few days. Triclopyr is most effective when applied to actively growing plants. Woody plants treated late in the growing season are susceptible, but may not show injury symptoms until the following spring when leaves and stems fail to emerge or are greatly distorted.

Triclopyr is not strongly bound by soil particles, thus it could potentially leach into groundwater or run off into surface waters. However, it has rarely been detected in groundwater monitoring surveys. Triclopyr has residual herbicidal activity in soils (half-life approximately 6 weeks). Desirable plants can be injured by spray drift, or if their roots are exposed to triclopyr in the soil. Triclopyr has low to moderate toxicity to humans and wildlife.

Addition of a non-ionic surfactant [0.5 fl. oz. per gallon] to the spray tank will enhance herbicidal activity of triclopyr. Before applying CROSSBOW in a pasture, read the label restrictions on the number of days required before allowing animals to graze or hay to be harvested in treated areas.
Triclopyr has herbicidal activity on aquatic vegetation, but a formulation for aquatic weed control in development has not yet been approved by EPA.

Which of these herbicides is appropriate to use for a given situation? The following list highlights some of the specific advantages of glyphosate and triclopyr:

GLYPHOSATE:
1) Controls invasive grasses such as Phragmites.
2) No soil activity - will not injure desirable plants via root uptake, rapidly deactivated and biodegraded in soil.
3) Very low health and environmental risks.
TRICLOPYR:
1) Does not kill grasses or sedges, thus unlikely to result in bare ground situation.
2) More effective than glyphosate on some woody species (eg. Oriental bittersweet, black locust).
3) Often provides better early-season control of perennial weeds.

 

CHEMICAL CONTROL STRATEGIES FOR INVASIVE PLANTS
The following products are readily available to homeowners and other property owners. Herbicide dosages (rates) mentioned in this guide refer to the product formulations listed below:

For GLYPHOSATE:
ROUNDUP Super Concentrate, ROUNDUP PRO, ROUNDUP ULTRA (41% active ingredient)

 

For TRICLOPYR:
ORTHO BRUSH-B-GON Poison Ivy, Poison Oak & Brush Killer1 (8% active ingredient)

 

Other Herbicides:
Glufosinate-ammonium: FINALE (11.33% active ingredient)
Potassium Salts of Fatty Acids: SAFER Superfast Weed & Grass Killer
Use the following volume measurements when mixing herbicide solutions:
2 tablespoons (Tbsp.) = 1 fluid ounce (fl. oz.) = 30 milliliters
8 Tbsp. = ½ cup = 4 fl. oz.
1 cup = 8 fl. oz.
2 cups = 1 pint (pt) = 16 fl. oz.
2 pt = 1 quart (qt) = 32 fl. oz.
4 qt = 1 gallon (gal) = 128 fl. oz.
WARNING: Spoons or containers used to measure herbicides should not be used to dispense any food, beverage or medicine.
The efficacy of ROUNDUP and BRUSH-B-GON will be optimized by adding a non-ionic surfactant (0.5 fl. oz. per gallon) to the spray tank.
Repeated applications may be necessary to achieve adequate control, especially of deep-rooted perennial and woody species. Stump or basal bark treatments will reduce re-sprouting of woody plants.

 

General References for Management of Invasive Plants:
Invasive Plants: Weeds of the Global Garden. 1996. J. M. Randall and J. Marinelli, eds. Brooklyn Botanic Garden Publications, Inc.
Mervosh, T. L. 1998. New England guide to chemical control of problem weeds and brush around homes and on non-cropland. Univ. of New Hampshire, Cooperative Extension. 7 p.
Weed Control Manual, Vol. 32. 1999. Meister Publishing Company. Willoughby, OH.