Controlling Undesirable Woody Plants: Part 1

Method is typically mechanical or chemical and mode is either broadcast or selective. Each treatment can be described by a method and a mode.

Editor’s note: This is part one of a two-part series on integrated vegetation management. This column will cover the topic of the treatment attribute and selective manual mode Check with your state’s cooperative extension or regulatory agency about legal herbicide use. 

American beech and many other native and non-native woody plants can dominate a woodland, exclude or limit the regeneration of desired plant species, and limit the biodiversity of the site. In high abundance, these species can complicate access for maple producers. Often these interfering species gain dominance because of selective deer browsing of desired plant species, and prolonged deer pressure can create a legacy effect that persists even if deer impacts are controlled.

In all forest vegetation management situations not exclusive to beech, you should start with a plan that details the interfering species, the desired plant species, the costs, how the interfering vegetation will be treated and how the site will be revegetated. Webinar archives detailing the vegetation management planning process are available at our YouTube page (ForestConnect).

The word “treatment” is used here to describe the way the vegetation is manipulated, often with the goal of killing the stems causing the interference. The treatment has two attributes — the method and the mode.

Method is typically mechanical or chemical and mode is either broadcast or selective (this column will concentrate on selective). Each treatment can be described by a method and a mode. First, we will review some principles, then consider some examples.

Which method and which mode?

Both mechanical and chemical methods have useful applications (see figure).

Often the choice depends on the attitude of the owner, the time of year, the terrain or the equipment. For some circumstances, a mechanical method is followed by a chemical method. Mechanical methods might include hand-pulling, brush saws and chain saws, timber ax and Fecon mowers, or livestock. Chemical treatments are herbicides, a type of pesticide that targets plants.

The decision about whether to use chemical methods may be decided by the owner’s attitudes and comfort with the use of herbicides. Some owners, such as maple producers who are certified organic, are restricted from using most conventional herbicides. Herbicides are regulated by the EPA through authority given to the state-level regulatory agencies. The regulatory process helps inform users about the known ways that the active ingredients will behave in the environment. If an owner uses an herbicide, they should carefully follow the label.

Of particular consideration is whether the herbicide has soil activity. Soil activity may result in injury or death of adjacent nontarget stems. Home recipes of chemical concoctions should never be used.

Mode is selected depending on the desired specificity of the treatment to individual or groups of stems (we will concentrate on selective treatment). A selective treatment affects individual stems. If an interfering species is mixed with a high percentage of a desired species, a selective treatment may be used to reduce injury to the desired species.

Selectivity is possible through physically isolating one stem from others, by using a treatment that only affects a certain species or by applying a treatment at a time of year when desirable species are not susceptible.

The principle to consider here is the fixed cost to visit each stem in a selective treatment. If there are too many stems per acre, that means (1) the cost per acre will become prohibitive, and (2) because there are a fixed number of stems per acre the interfering stems have likely displaced the desirable stems and a broadcast treatment would have limited relative collateral damage.

Selective manual

Types of treatments would include pulling, girdling or cutting:

Pulling treatments are best applied in circumstances of small plants, where the interfering plant has only recently been established and there is little potential for subsequent seed input from that plant.

Girdling severs the phloem and vascular cambium just inside the bark. Girdling can be accomplished with an ax, saw or flame torch; chemical girdling is called basal bark and described as follows. Girdling has the advantage of more quickly treating the stems as compared to cutting and not needing to immediately address the downed stem. Stem size matters because a large dead tree may become a hazard in the future.

Cutting uses a saw to sever the stem and fully disconnect the foliage from the roots. Traditional timber stand improvement with firewood as a product is an example of this treatment.

Selective chemical

Types of treatments include foliar, hack-and-squirt (aka injection), cut-stump and basal bark. Selective chemical may also be integrated with selective manual. Treatments can be quick, cost-effective and reduce or typically eliminate the potential for post-treatment sprouting from stumps or roots.

Foliar treatments are applied to individual plants. Applications of foliar sprays on tall or broad plants may result in overspray and a heightened potential for drift onto adjacent plants. Foliar treatments are commonly a low concentration of glyphosate (e.g., Roundup) or triclopyr (e.g., Garlon 4 ultra) perhaps mixed with imazapyr (e.g., Arsenal, Polaris AC) or sulfometuron methyl (e.g., Oust). The herbicide labels will describe mixing ratios. Foliar treatments can be applied following a mechanical cutting, after stems sprout new foliage, thus allowing for the use of less chemical and greater control.

Hack-and-squirt treatments use a hatchet or similar tool to expose the phloem, vascular cambium and outer most xylem tissues, the wood, to a fairly concentrated (25 to 50 percent active ingredient) application of glyphosate. Imazapyr might also be used to control some species. The role of the hatchet is to expose the inner wood; other tools might include a portable drill or divots made by a chainsaw. The objective is to make multiple, relatively small wounds that receive an application of the herbicide.

Cut-stump treatments are appropriate when the stem is severed, but stump or root sprouts will occur without additional treatment. Herbicides might include glyphosate or triclopyr. Glyphosate is mobile in the root system and will be translocated from the stump to root sprouts that are controlled. Triclopyr is less mobile than glyphosate. Follow label details, but herbicides are typically applied to the outer 2 inches of the freshly cut stump surface or to the entire surface and sides of the stump.

Basal bark treatments use an herbicide, typically triclopyr, in an oil-based carrier to chemically girdle a stem.

ForestConnect is a joint research and extension program funded by the Cornell University Agricultural Experiment Station (Hatch funds) and Cornell Cooperative Extension (Smith Lever funds) received by Cornell University College of Agriculture and Life Science from the National Institutes for Food and Agriculture (NIFA,) U.S. Department of Agriculture.

Photo: iStock/HowardOates