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Forest Herbicides for Vegetation Management

Forest Herbicide Prescription Recommendations 

A new support tool for forest herbicide prescription selection is now available. The manual describes herbicide prescriptions in light of a specific management context. The new tool will help forest managers make more informed decisions regarding applications to forests.

Download the Forest Herbicide Recommendations

Competing vegetation or competition is always a concern in forest management. Controlling competition to crop trees (e.g. pine or oak seedlings) in forest management is an essential management operation that will assist in optimizing production and revenue from timber management. Many forest researchers believe competition control provides the most benefit to survival and growth over any silvicultural (forest management) method available. Specific benefits of competition control include:

  • Increased nutrient availability to crop trees
  • Increased water availability
  • Increased sunlight availability
  • Increased seedling survival
  • Increased growth rates
  • Shorter rotation lengths
  • Increased revenues

Common Questions Regarding Herbicide Applications

What are the Primary Concerns with Herbicide Applications in Forestry?

A photo of invasive grass and weeds

Grasses and broadleaf weeds can be serious competitors for planted seedlings.

Photo by: Kyle Cunningham, University of Arkansas - Division of Agriculture

There are many herbicides available for use in forest management operations. Each herbicide is designed for specific uses. Several considerations should be made prior to making an application, including species, site conditions and environment.

Species Concerns:

  • What are the crop trees?
    • Pine or hardwood
      • species requirements -resistance/susceptibility
  • What are the primary competitors?
    • Grasses
    • Broadleaf weeds
    • Vines
    • Shrubs
    • Other tree species

 Site Conditions:

  • Size of area to be treated
    • Effects method of application, whether a contractor is needed and cost.
  • Topography
    • Steep terrain can create difficulty in ground applications.
  • Structure of vegetation present
    • Effects equipment used in application.
  • Soil type
    • Soil texture and drainage can impact how effective some herbicides will be.
  • Wildlife habitat
    • Forestry herbicides usually exhibit low toxicity to animals. Habitat alterations are most important and they could be positive or negative to wildlife.
  • Sensitive areas
    • Endangered species, water sources, crops, and other sensitive areas should be identified and protected from herbicide applications.

 Environment:

man measuring small pine tree

Herbicide applications can increase both survival and growth of planted seedlings.

Photo by: Kyle Cunningham, University of Arkansas - Division of Agriculture

  • Weather conditions
    • Some herbicides require rainfall to be active, while too much rainfall can wash away others.
  • Timing of application
    • Soil active herbicides are typically applied early in the year, while foliar active herbicides may be more effective from mid to late in the growing season.
  • Risks of misapplication 
    • Applying incorrectly or movement after application (runoff, etc..) may injure sensitive areas nearby.

What are the Types of Applications Made in Pine Stands?

  • Site preparation prior to planting
    • Controlling competing vegetation prior to planting is much easier than post planting. Furthermore, there will be many more application rate options available prior to planting. 
  • Release from hardwood competition
    • There are two times to release pines from hardwood competition 1. During establishment (first year or two) and 2. prior to a fertilization treatment at mid-rotation (~15 years in rotation).
  • Herbaceous weed control
    • In the first year after seedlings are planted, grasses and broadleaf weeds can effect survival and growth. Several herbicides are available to spray over the top of pine trees. Again, these will be lower rates than could have been applied at site preparation. 

What are the Types of Applications Made in Hardwood Stands?

  • Site preparation prior to planting
    • There are fewer herbicides that can be used on hardwood plantings than in pine. Apply foliar active only herbicides in late growing season (prior to planting in the following spring) to control competing vegetation. A couple of soil active herbicides are available to apply just prior to planting in late winter to early spring. Once hardwood seedlings break bud in spring, only grass herbicides may be applied.
  • Herbaceous weed control
    • Again this is most effectively addressed prior to planting. Grasses may be controlled by a few grass herbicides after leaf out. Options for competition control during the growing season are extremely limited with hardwood seedlings
  • Timber Stand Improvement (TSI)
    • This operation is typically performed in existing stands to improve species composition and increase sunlight reaching developing desirable regeneration. TSI is performed by applying herbicide to individual undesirable stems.
photo of a man preforming a Herbicide Injection

TSI can be performed using herbicide injection of individual trees.

 photo of a forest showing Increased light from injection of midstory

 

Presentation: Competition Control in Hardwood Stands 

What About Controlling Non-native Invasive Forest Plants?

royal paulownia non-native invasive species plant
Royal paulownia is a serious non-native invasive.
  • A good time to address invasive plants is during site preparation, when herbicide rates and application rates are most versatile.
  • The type of herbicide and application method can differ based on the species of concern
  • Some common invasive plants important to forestry
    • Kudzu
    • Callery pear
    • Chinese and Japanese privet
    • Royal paulownia or empress tree
    • Ailanthus or tree of heaven
    • Japanese honeysuckle
  • Non-native invasive plants can have significant impacts on forest production. Identifying these pests and taking fast, aggressive and repeated actions are essential in controlling invasive plants and reducing the costly impacts they can have on forests (Arkansas Invasives and USFS Non-native Invasive Plants of Southern Forests).

 

What are the Application Methods?

  • Aerial application
    • Typically performed on large acreages, steep terrain, or heavy vegetative cover using a helicopter mounted sprayer.
  • Broadcast ground applications
    • These applications are carried out using a skidder, tractor, or four wheeler, depending on size of area and vegetative structure.
  • Banded and spot ground applications
    • Can be performed with a four wheeler for banding and/or backpack/handheld sprayers for spot spraying.
  • Directed sprays
    • Directed sprays are performed with a backpack or handheld sprayer and are sprayed only on competition. Care is taken to avoid herbicide contact with seedlings. 
helicopter flying through forest performing an aerial application tractor spraying herbicide in a pasture
Photo of a field after a herbicide application

Aerial, broadcast ground and banded ground applications

Properly planned and implemented herbicide applications can be very useful in forest management. Improperly planned and/or misapplication can be harmful and costly. Therefore, taking steps to ensure proper application are essential.

What Steps Should I Take Prior to Making a Herbicide Application?

  • Identify the crop species (for example loblolly pine).
  • Identify major competition sources (grasses, broadleaf weeds, woody plants, vines).
  • Identify specific species to be controlled.
  • Identify sensitive areas.
  • Consult a registered forester about the need for an herbicide application.
  • Consult a licensed herbicide applicator about making an application.
  • ALWAYS ADHERE TO THE HERBICIDE LABEL!

A list of vendors by service type and county can be viewed at: Arkansas Forestry Commission

Publications

MP553 Forestry Herbicide Prescriptions

MP-44 Arkansas Herbicide Prescription Manual

USFS Non-native Invasive Plants of Southern Forests

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