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.

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.

For all these 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

1. Herbicide label directions must be carefully followed.
2. Protective gear should be worn as per the label directions.
3. Herbicides must be labeled and stored appropriately, and used containers must be disposed of properly.
4. 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.
5. If an herbicide is used in a public area, notices must be posted near all treated areas.
6. Livestock should not be permitted in treated areas until the herbicide has dissipated.
7. Wind speeds must be less than 10 mph to minimize herbicide drift.
8. 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.
9. Personnel who function as commercial herbicide contractors must be certified.

Wisconsin DNR web page on herbicide use and certification: http://dnr.wi.gov/org/land/er/invasive/info/herbicides.htm

Examples of herbicide use for invasive plants

1. 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.
2. Glyphosate is a broad-spectrum herbicide and kills virtually all plants within 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.
3. 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.
4. 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.
5. 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.
6. 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.
7. Imazapic will control most broadleaf weeds as well as cool-season grasses such as smooth brome and quack grass.

Summary

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. Use of herbicides as part of an integrated system for control of honeysuckle, buckthorn, and garlic mustard are given elsewhere on this web site.

(Content by Thomas D. Brock)

For information on herbicide use designed for landowners, see the Wisconsin DNR Forestry site.

Recommendations for chemical control of noxious weeds using backpack and hand held sprayers

Herbicide Database

Note: some DNR county foresters informally will loan out backpack sprayers.