Herbicides are an invaluable tool in forest management for controlling undesirable vegetation. To use them safely and effectively, one must understand a few basic principles. This article is the first in a series of articles on herbicides for forestry applications. To start, we will look at the basic principles one must understand to utilize herbicides. Then, in future newsletters, we will look at specific herbicides commonly used in forest management.
First and foremost, the user must read the label of any herbicide they plan to use. The label is the law and provides directions on how the herbicide can be used safely and effectively. Not following the label can result in poor control, damage to the environment, damage to equipment, and can be harmful to the user. These are just a few of the consequences that can occur from not reading the label. READ THE LABEL.
I will admit that the labels are not always easy to read, and some of the terminology is hard to understand. So, let’s look at some of the terminology you may encounter on a herbicide label.
- Pre-emergent vs. Post-emergent
a. Pre-emergent – interrupts seed germination and keeps new weeds from developing. Typically, pre-emergents do not control established plants.
b. Post-emergent – are applied after the plant has become established and typically has leaves. Post-emergents are most effective when applied to plants that are actively growing. - Residual vs. Non-residual
a. Residual – herbicides that continue to be active for days, weeks, or months after application. These herbicides provide extended control.
b. Non-residual – herbicides that do not leave an active residue in the soil after application. - Selective vs. Non-Selective
a. Selective – herbicides that target a select group of plants.
b. Non-selective – herbicides that can affect any plant on which it is applied. - Contact vs. Systemic
a. Contact – herbicides that must come in contact with the plant and affect the treated part of the plant.
b. Systemic – herbicides that are translocated through the plant and can be absorbed by the roots or foliage. - Personal Protective Equipment (PPE) will be listed on the label and is legally required to be worn to protect the person applying or mixing the herbicide to protect them from contact with the herbicide.
- Active Ingredient is the component that is responsible for the herbicide’s toxicity. It is the ingredient that controls unwanted vegetation.
- Signal Words are located on the label to describe the degree of toxicity to the user.
a. Danger – highly toxic
b. Warning – moderately toxic
c. Caution – slightly toxic - Surfactants are adjuvants that facilitate and accentuate the herbicide’s emulsifying, dispersing, spreading, wetting, or other surface-modifying properties. In other words, they make the herbicide work better.
a. Anionic Surfactant – enhances foaming and other spreading properties.
b. Cationic Surfactant – often toxic to plants.
c. Amphoteric Surfactant – used to match pesticide formulations to carrier components.
d. Nonionic Surfactant – most commonly used and does a good job of breaking water surface tension.
The label will also give us rate recommendations based on application techniques. Common application techniques in forestry are foliar, basal, hack and squirt, and cut stump.
Foliar application applies the herbicides onto the leaves of the plant. This is typically done in the growing season when leaves are present and the plant is actively growing. Application equipment usually includes a hand sprayer, backpack sprayer, or ATV/tractor sprayer. Foliar application can be highly effective on smaller vegetation and can quickly cover large areas. Typically, complete coverage of the foliage is essential for control.
Basal application applies the herbicide to the lower 12-18 inches of the stem. The stem must be treated on all sides. A penetrant oil is also required to help move the herbicide through the bark and into the growing layer of the stem. The same equipment used for foliar can also be used for basal applications. Typically, stems need to be less than six inches in diameter and can be applied at any time of the year.
Hack and squirt applies the herbicide into an angle cut made into the tree’s stem. A machete or hatchet can be used to make the angle cut, and the herbicide can be applied to the cut with a spray bottle. Hack and squirt is a highly selective method and can be used for larger trees that may be hard to treat with other methods. Applications can be made almost any time of the year except for spring when the sap is flowing. More information on hack and squirt can be found in the article at the following link: https://blogs.clemson.edu/fnr/2021/07/07/using-hack-and-squirt-method-to-control-undesirable-vegetation/
Cut stump applies the herbicide to a freshly cut stump or stem. The herbicide should be applied immediately after cutting the vegetation. A sprayer, paint brush, or spray bottle can be used to apply the herbicide. This can be done at any time of the year and greatly reduces resprouts or kills the stem.
When using herbicides, it is essential to maintain your equipment properly. Equipment should be cleaned after each use by triple rinsing. Equipment should also be calibrated regularly to ensure the labeled herbicide rate is applied to the correct area. Janet Steele has a fact sheet that describes how to calibrate a backpack sprayer at the following link: https://lgpress.clemson.edu/publication/backpack-sprayer-calibration-for-forestry-uses/
Reading the label is just the start of understanding how a herbicide works. The user should identify the vegetation to be controlled, what kind of soils they have, and any sensitive areas that may need to be protected. Wind can play a part in the application, as we typically avoid high winds to prevent spray drift. While this article cannot cover all things needed for herbicide application, it is a start to a better understanding. Look for future articles that will go more in-depth about the herbicides commonly used in forestry.
Check out our YouTube page for our Herbicide How-To Series on the different herbicide applications- https://youtube.com/playlist?list=PLZcWRaJdKpm0ZgHNdqAyB04V-y5jRhngr&si=ws2mwB4DMbKD1CEm
Author(s)
Jeff Fellers, Cooperative Extension, Forestry and Wildlife Agent
This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas.
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