Herbicides are an important component of integrated vegetation management programs on natural areas, trails and roadsides. This section includes technical information on herbicides in the pyridine chemical family that have a synthetic auxin/growth regulator mode of action (http://bit.ly/herb_performance). Herbicide use rate, formulation, and attributes are described and questions regarding aminopyralid and triclopyr herbicides are discussed.
TECHNICAL FACTS ABOUTHERBICIDES
Herbicides are formulated to include the active ingredient (chemical that inhibits growth or kills the plant) and inert ingredients. Active ingredients include aminopyralid (Milestone®), aminopyralid plus metsulfuron (Opensight®), triclopyr (Vastlan™, Garlon® 4 Ultra, Pathfinder® II), clopyralid (Transline®), and fluroxypyr plus triclopyr (PastureGard® HL). These herbicides are absorbed by leaves, stems and roots and are translocated (moved) throughout the plant accumulating in meristematic tissue. Herbicides listed in this section have soil residual activity with the exception of triclopyr and fluroxypyr.
HERBICIDES CONTAINING AMINOPYRALID
HERBICIDE CONTAINING CLOPYRALID
One gallon of Milestone herbicide contains 2 pounds (lbs) acid equivalent (ae) of aminopyralid.
USE RATE RANGE
3 to 7 fluid ounces of product per acre. Spot treatments may be made up to 14 fl oz/ac per annual growing season; however, not more than 50% of an acre may be treated when using this rate.
Milestone provides excellent post-emergent and residual control of over 70 broadleaf weeds and woody plants.
Opensight is a dry formulation that contains both aminopyralid and metsulfuron methyl.
USE RATE RANGE
1.5 to 3.3 ounces of product per acre. Spot treatments may be made up to 6.6 oz/ac per annual growing season however, not more than 50% of an acre may be treated when using this rate. The dry formulation requires the addition of a surfactant (NIS, MSO, COC) for effective control.
Opensight herbicide provides excellent post-emergent and residual control of over 160 broadleaf weeds and woody plants including many difficult to control invasive or noxious weeds.
One gallon of Transline contains 3 lb ae of clopyralid.
USE RATE RANGE
1/4 pint to 1.33 pints of product per acre.
Transline offers excellent control of target invasive and noxious weeds and certain woody plants, while providing the greatest selectivity to many tree (except legume species), brush, and grass species.
HERBICIDE CONTAINING TRICLOPYR
ACTIVE INGREDIENT One gallon of Vastlan contains 4 pounds acid equivalent per gallon (lbs ae/ gallon) of triclopyr choline.
USE RATE RANGE
0.75 pints to 9 quarts of product per acre.
Apply no more than 2 quarts of Vastlan per acre per growing season on range and pasture sites, including rights-of-way, fence rows or any area where grazing or harvesting of hay is allowed.. On forestry sites, Vastlan may be used at rates up to 6 quarts per acre per year. For all terrestrial use sites other than range, pasture, forestry sites, and grazed/hayed areas, the maximum application rate is 9 quarts of Vastlan per acre per year.
Vastlan is a broad-spectrum herbicide with excellent activity on brush and some emerged broadleaf weeds, with no residual soil activity.
One gallon of Garlon 4 Ultra contains 4 lb ae of triclopyr formulated in a plant-based oil carrier as a low volatile ester.
USE RATE RANGE
1 to 4 quarts of product per acre broadcast to foliage or mixed as a percent solution in water or basal oil for woody plant treatments (see label by species).
Garlon 4 Ultra controls many woody plants, and has no residual soil activity.
One gallon of Pathfinder II herbicide contains 0.75 lb ae of triclopyr ester (13.6%) formulated in a plant-based oil carrier.
Pathfinder II herbicide is a ready-to-use (no mixing required) herbicide for low-volume basal and cut-stump application of woody plants in forests, rangeland, permanent pasture and non-crop areas. Not intended for foliage applications.
One gallon of PastureGard HL herbicide contains 3 lb ae triclopyr ester and 1 lb ae fluroxypyr formulated as an oil soluble, emulsifiable concentrate.
USE RATE RANGE
3/4 pint to 4 pints of product per acre.
PastureGard HL provides excellent selective control of many woody plants and broadleaf weeds such as sericea lespedeza and kochia. The herbicide is not harmful to established grasses and many forbs, and can be applied under the canopy of desirable trees.
HERBICIDES CONTAINING GLYPHOSATE
One gallon of Accord XRT II contains 4.0 lb ae of glyphosate formulated as an IPA salt, and 12.4% of a patented surfactant blend.
USE RATE RANGE
The maximum use rate is 2 gallons of product per acre per year.
Provides excellent non-selective post-emergence control of annual, biennial, and perennial weeds, vines, and woody plants in forests and non-crop sites. Contains a unique surfactant to enhance woody plant control. The high load formulation is easy to handle with low-foaming characteristics. No grazing/haying restrictions for dairy animals or other livestock. May be used around non-irrigation ditch banks, seasonally dry wetlands, flood plains, marshes, swamps. Do not apply to open water areas.
One gallon of Rodeo contains 4.0 lb ae of glyphosate formulated as a DMA salt.
USE RATE RANGE
Maximum terrestrial use rate is 2 gallons of product per acre per year.
Approved for aquatic and wetland sites with an appropriate aquatic surfactant. Provides non-selective control of emerged aquatic vegetation; annual, biennial, and perennial weeds; vines; and woody plants. Excellent tank mix partner. Binds readily to soil so may be used under the tree canopy without concern of tree damage. Can be used for foliar, cut stump, tree injection/hack and squirt, and grass growth suppression.
What is the environmental fate of Milestone®?
Soil: Aerobic microbial degradation is the primary route of breakdown in soil. Average field soil half-life is 34.5 days for eight North American sites. There are no degradation metabolites of concern.
Water: Photolysis (UV portion of the light spectrum) is the primary route of degradation in water. Photolysis half-life under standard conditions is 0.6 days. Groundwater contamination potential is low because of low use rates combined with moderate soil half-life.
Air: Practically non-volatile
Where can Milestone® be used?
Milestone is labeled for use on rangeland, permanent grass pastures, Conservation Reserve Program (CRP) acres, non-cropland areas (such as roadsides), non-irrigation ditch banks, seasonally dry wetlands, natural areas (such as wildlife management areas, wildlife openings, wildlife habitats, recreation areas, campgrounds, trailheads and trails), and grazed areas in and around these sites.
What is the runoff potential of Milestone®?
Milestone has a low risk of runoff in surface water compared to the current market standards. The runoff impact of Milestone is mitigated by low use rate and rapid photolysis in water.
What is the ecotoxicology profile of Milestone®?
- Milestone exhibits low acute and chronic toxicity to mammals, birds, fish, aquatic and terrestrial invertebrates, algae and aquatic vascular plants in laboratory studies.
- Risk of adverse effects is substantially below all of the EPA levels of concern (LOC) for non-target organisms.
- Milestone produces no significant soil or water metabolites other than CO2 and NH3 and has a low bioaccumulation potential.
- In EPA’s assessment under the Reduced Risk Pesticide Initiative, Milestone was found to have reduced acute and chronic toxicity to mammals, birds, algae and aquatic vascular plants compared to market standards.
What is the rainfast period?
Foliar absorption of Milestone applied post emergence is relatively rapid. Milestone herbicide appears to be rainfast within two hours after application when applied at recommended label rates.
How close to water can I spray?
Milestone can be used to the waters edge but do not apply directly to water or to areas where surface water is present or to intertidal areas below the mean high water mark. Take precautions to avoid spray drift onto water. Do not spray on inner banks of ditches or canals used to transport irrigation water.
It is permissible to treat non-irrigation ditch banks, seasonally dry wetlands (such as flood plains, deltas, marshes, swamps, or bogs) and transitional areas between upland and lowland sites.
Can Milestone® be used in riparian areas?
Yes, under the following guidelines:
- The label does not allow applications directly to water (ponds, lakes, rivers, streams and irrigation canals).
- Avoid applications that may result in movement of Milestone into water used to irrigate crops.
- The non-target plant community should be considered (see forb and shrub tolerance section, page 8).
How long does Milestone® persist in the soil?
- While Milestone herbicide will provide season-long residual control of emerging broadleaf weeds, this herbicide has a moderate field soil half-life.
- Half-lives in U.S. and Canadian field studies have averaged approximately 34.5 days. Ninety percent of Milestone applied at a rate of 7 fl oz/acre dissipated within 90 days.
- In a large majority of studies, the herbicide has remained in the top six to 12 inches of the soil profile.
What effect does pH have on degradation of Milestone®?
Due to the low pKa (ionization constant) of the active ingredient, pH will have no impact on Milestone degradation in any matrix.
Can Milestone® be applied with spot treatments?
Yes, spot treatments may be made at an equivalent broadcast rate of up to 0.22 lb active ingredient (14 fl oz of Milestone) per acre per annual growing season; however, not more than 50% of an acre may be treated.
Do not apply more than a total of 0.1 lb active ingredient per acre (7 fl oz per acre of Milestone) per annual growing season. (See resource for spot treatment calibration guidelines on page 12.)
What about surfactants?
The addition of a high quality non-ionic surfactant (of at least 80% active ingredient) at 0.25 to 0.5% volume per volume (1 to 2 quarts per 100 gallons of spray) is recommended to enhance herbicide activity under adverse environmental conditions (such as high temperature, low relative humidity, drought conditions, dusty plant surfaces), when weeds are heavily pubescent, or with more mature plants.
How long will Milestone® remain active in the spray tank solution?
Milestone is not degraded by the hydrolysis process like sulfonylurea herbicides. Milestone will break down in water when exposed to ultra-violet (UV) light from the sun. Provided the spray tank is a UV resistant tank (most are), or if the sprayer or mix tank is parked inside, the solution would be stable for very long periods of time. Although once herbicides are mixed, it is advisable to use them as soon as possible
Are there sprayer clean-out instructions to avoid damage to sensitive plants?
Yes. It is important to not use spray equipment used to apply Milestone for other applications to land planted to crops or desirable sensitive plants unless it has been determined that all residues of this herbicide have been removed by thorough cleaning of equipment. No exceptions! See label for detailed cleaning instructions.
Will Milestone® harm established grasses?
Research was conducted on over 33 different grass species and both warm and cool season grasses show excellent tolerance to Milestone. In fact, grass production increases significantly after weeds are removed.
Are there grazing or haying restrictions?
There are no restrictions on grazing (any livestock including lactating dairy and horses) or hay harvest following application of Milestone at labeled rates1.
Milestone passes through an animal’s digestive system unchanged and is excreted in urine and manure. This occurs relatively rapidly, within about three days.
Cutting hay too soon after spraying weeds will reduce weed control. Wait 14 days after herbicide application to cut grass hay to allow herbicide to work.
Milestone does not break down in plants. Therefore, hay from areas treated with Milestone may contain residues. Inform the recipient of hay or manure from animals grazing pastures or feeding on hay from areas treated with Milestone of the label use precautions and restrictions.
Hay from grass treated with Milestone within the preceding 18-months can only be used on the farm or ranch where the product is applied unless allowed by supplemental labeling.
Do not transfer livestock from treated grazing areas to sensitive broadleaf crop areas without first allowing three days of grazing in an untreated pasture. Otherwise, urine and manure may contain enough Milestone to cause injury to sensitive broadleaf plants. Refer to Milestone label for additional instructions.
1 Restrictions do apply to the transfer of grazing animals to sites intended to grow sensitive crops. Refer to the label for a complete list of transfer restrictions.
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Always read and follow label directions.
Milestone has no grazing or haying restrictions for any class of livestock, including lactating dairy cows, horses (including lactating mares) and meat animals prior to slaughter. However, label precautions do apply to forage treated with Milestone and to manure from animals that have consumed treated forage within the last three days. Consult the label for full details. Some states require an individual be licensed if involved in the recommendation, handling or application of any pesticide. Consult your local Extension office for information regarding licensing requirements. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state.
Opensight specialty herbicides: When treating areas in and around roadside or utility rights-of-way that are or will be grazed, hayed or planted to forage, important label precautions apply regarding harvesting hay from treated sites, using manure from animals grazing on treated areas or rotating the treated area to sensitive crops. See the product label for details.
State restrictions on the sale and use of Garlon 4 Ultra, Opensight, Accord XRT II and Transline apply. Consult the label before purchase or use for full details.