Herbicides for Weed and Brush Control in Natural Areas
Several herbicides are well suited for use in weed and brush control in natural areas. The herbicides discussed here have been carefully established to be safe and effective if used properly. Before using any herbicide, it is essential that the label be read completely and its specifications followed.
Purpose and Need
Herbicides are used to facilitate restoration in prairie and savanna ecosystems in conjunction with other methods, including hand pulling, mowing, cutting, prescribed burning, seeding, and cultivation. Herbicides should be used as part of an integrated weed management strategy. The precise treatment method used will depend upon the target species, its life history, the extent of the problem, and the compatibility of the herbicide with the restoration objectives.
Why use Herbicides?
Invasive plants are a threat to management and restoration of natural ecosystems. In many areas, due to neglect over many years, existing native vegetation has become heavily infested with invasive species. Most of these invasive species are nonnative, having been introduced from Europe, Asia, or other distant places. Examples of exotic species include sweet clover, wild parsnip, reed canary grass, purple loosestrife, garlic mustard, honeysuckle, buckthorn, and Kentucky bluegrass. The picture to the right is of buckthorn that was cut but not treated with an herbicide.
Some native plants are unusually invasive and may also be a threat to ecosystem function. Examples of native invasive plants include smooth sumac, gray dogwood, hawthorn, sandbar willow, and prickly ash.
Invasive plants compete with desired species for light, nutrients, and moisture. They may alter hydrological regimes in wetlands, or alter the structure of upland plant communities. Although invasive plants can be removed without the use of herbicides, in many cases the cost is prohibitive. In some situations, herbicide use is essential.
Only Non-Aquatic Habitats Discussed Here
The discussion here deals only with non-aquatic habitats. Some herbicides are approved for use in aquatic habitats, but the kinds, uses, and requirements are different.
Spot Spraying and Broadcast Spraying
For most herbicide applications in natural areas, spot spraying is preferred. This permits application of the chemical just to target species. Foliar application should be made with a low-pressure (20-50 psi) backpack sprayer equipped with a wand applicator. A sprayer nozzle which creates a flat or cone-shaped pattern is preferable. The herbicide should be allowed to dry for at least two hours to ensure adequate absorption. (Do not spray when rainfall is threatened.) Addition of a nonionic surfactant to the mixture helps ensure complete leaf coverage and increases the rate of absorption. The herbicide should thoroughly cover the foliage but not to the point of run-off. Personnel applying herbicide must be properly trained and knowledgeable about the native vegetation.
Broadcast spraying in natural area restoration is used primarily when a fallow field is to be planted to prairie. It must be ascertained first that all of the existing vegetation is undesirable. The field can then be treated with a nonspecific herbicide such as glyphosate, which kills all existing vegetation. A boom sprayer towed behind a tractor is usually used.
Summary of Approved Herbicides
The table below summarizes the characteristics of seven herbicides commonly used for the control of invasive plants and noxious weeds in prairie restoration activities.
|Herbicide||Trade Names||Target Species||Unaffected Species||Environmental Characteristics|
|2,4 D||Generic||Broadleaf herbaceous plants||Most monocots, including grasses||Half-life in soil: 7-10 days; safe for aquatic uses|
|Glyphosate||Generic||Nonselective; grasses, forbs, vines, trees, shrubs||None||Half-life in soil: several weeks; is inactive by soil particles|
|Sethoxydim||Vantage||Grasses||Broadleaf herbs, sedges, woody plants||Half-life in soil: 5 days|
|Triclopyr||Garlon||Broadleaf herbs, woody plants||Most monocots, including grasses||Half-life in soil: 30 days|
|Clopyralid||Transline||Broadleaf weeds||Grasses||Half-life in soil: 40 days|
|Fosamine||Krenite||Woody plants||Herbaceous plants less affected||Rapid degeneration and binding to soil particles|
|Imazapic||Plateau||Grasses, some broadleaf species||Many broadleaf species||Half-life in soil: several months|
For all herbicides, the label should be read and followed.
It should be emphasized that herbicide use should be used as part of a total management system. As the table shows, none of these herbicides is completely specific. Care must be taken to ensure that sensitive non-target species are not treated.
Procedures for Herbicide Use
- Herbicide label directions must be carefully followed.
- Protective gear should be worn as per the label directions.
- Herbicides must be labeled and stored appropriately, and used containers must be disposed of properly.
- Empty containers should be rinsed at least three times with clean water and the rinse water must be disposed of per Environmental Protection Agency (EPA) guidelines.
- If an herbicide is used in a public area, notices must be posted near all treated areas.
- Livestock should not be permitted in treated areas until the herbicide has dissipated.
- Wind speeds must be less than 10 mph to minimize herbicide drift.
- Areas to be treated should be surveyed first to ensure protection of non-target species. Only spot applications should be used in areas containing sensitive plant species.
- Personnel who function as commercial herbicide contractors must be certified.
Wisconsin DNR webpage on herbicide use for forest management.
Wisconsin DNR web page on aquatic herbicide use.
Examples of Herbicide use for Invasive Plants
- 2,4-D. This herbicide is widely used for weed control in lawns and other urban settings. It is active against broadleaf plants (dicots) only; grasses are unaffected. In natural areas, 2,4-D can be used for spot spraying broadleaf weeds such as wild parnsip. However, if there are desirable broadleaf species nearby, hand pulling is preferable.
- Glyphosate is a broad-spectrum herbicide that kills virtually all plantswithin a few days after spraying. Its use in natural area restoration is usually restricted to use to prevent woody plants from resprouting after they are cut. The cut stem (stump) is treated with a concentrated (20%) solution of glyphosate. The chemical moves to the roots and kills the root system. With care, the chemical is confined to the cut stem only, and nearby vegetation is not affected.
- At approved concentrations, sethoxydim is active only against grasses; neither sedges nor broadleaf plants are affected. It has been found effective in the control of reed canary grass in wetland situations.
- Triclopyr is widely used for the control of woody vegetation. Like glyphosate, it can be used to treat cut stems to prevent resprouting. One chemical form, Garlon 4, is soluble in oil and can be used to control woody vegetation by treatment of a zone of bark along the lower part of the trunk. The hydrophobic Garlon moves through the bark to the phloem and is translocated to the roots. This basal bark treatment is effective even in the winter. After treatment, the tree or shrub does not leaf out the following spring. Eventually the roots die and the plant topples to the ground.
- Clopyralid is unusually effective against plants of the legume and sunflower (Composite) family. It is used for the control of legumes such as crown vetch and black locust, and of composites such as Canada thistle and spotted knapweed. Although it is active against other plant species, the effective concentration required is much higher.
- Fosamine is used for control of woody plants such as brush and brambles in noncropland areas. It is applied as a foliage treatment during the growing season. Treated woody plants remain green for the remainder of the growing season but fail to leaf out the next spring.
- Imazapic will control most broadleaf weeds as well as cool-season grasses such as smooth brome and quack grass.
Properly used, herbicides have wide utility in elimination of invasive plants and the restoration of natural areas. For specific recommendations, consult the herbicide label or use the manufacturers advice.
(Content by Thomas D. Brock)
Note: some DNR county foresters informally will loan out backpack sprayers.
Native Forb and Shrub Tolerance to Milestone® VM Herbicide
Land managers consider the effect of Milestone VM on desirable native forbs and shrubs when making decisions about controlling invasive plants. Milestone VM is a broadleaf herbicide that has reduced risk to the environment compared with other commercially available herbicides, making it a desirable alternative for invasive weed control on rangeland and wildland sites.
Studies were established within diverse native plant communities in Montana, Colorado, North Dakota and Minnesota to determine long-term response of native forbs and shrubs when Milestone VM was applied in early summer or fall, and to develop a tolerance/susceptibility ranking for native plants.
- Most native forb species and shrubs were moderately tolerant to tolerant, or recovered following treatment with Milestone VM herbicide.
- Land managers can use these data as a guideline to evaluate risk to native plant communities when using Milestone VM for invasive species management.
- Milestone VM herbicide can be used to manage invasive plants in mixed plant communities and facilitate recovery of desirable forbs and shrubs.
- Historical data1 suggests that by the third or fourth year post-application, there would be little difference in non-target forb tolerance with only a few very sensitive forbs being adversely impacted in the long term.