Invasive Weed Management

Treatment: Strategies and Methods

Contents

Learning Objectives

[4] state in order the priorities in the recommended strategy for allocation of weed management resources; [5] state the categories of invasive weed treatments considered in integrated weed management, and identify sources for information about effective treatments for particular species.

Narrative

In most cases, the main obstacle to weed management is not the lack of effective treatment methodologies, but the lack of resources, (including funds, in-kind match, volunteer labor, landowners personal time) to implement them. Therefore the first step in developing a weed management strategy is to determine how to most effectively allocate available resources.
There is a tendency to want to tackle the biggest, baddest weeds first. However, research and practical experience have shown that the opposite is true. The fastest growing weeds are pioneer or satellite populations- small patches well separated from their source that have room to expand in all directions. In contrast, the high-density main body of the infestation is growing much more slowly because it is competing with itself for suitable habitat. The greatest return-on-investment of weed treatment efforts comes from treating the low-density populations first.
Many well-meaning efforts have invested significant resources into a short-term effort to manage weeds over a large area, only to find that in a few years the site has become reinfested and may actually be in worse condition than before due to disturbance. This unfortunate approach has actually been encouraged by funding agencies, which supply funds for a short-term effort and expects results in terms of acres treated. Funding agencies are reluctant to supply the funds for the followup work that is required to ensure that initial gains in weed reduction are not lost to reinfestation by the same or new weed species.
The following steps to allocating sources are recommended to be followed as closely as possible, within the constraints of available resources:
  1. prevention should be fully supported at the highest priority;
  2. maintenance of previous control efforts should be fully supported before initiating any new treatments;
  3. pioneer and satellite populations should be treated before tackling the main body of the infestation;
  4. sites with mostly-intact native vegetation populations and only low-density invasives should be treated next, allowing the native vegetation to fill in and resist later reinfestation;
  5. the main body of any infestations with moving fronts should be contained within a no-spread perimeter, similar to wildfire-fighting strategies. Moving fronts tend to appear in the middle stages of infestation and are governed by short-range dispersal mechanisms.
  6. Only after all of the above needs have been satisfied should one attempt to tackle large, high-density invasive weed populations;
  7. Understand your weed; hyperlinks provided below allow you to connect to websites that provide the latest understanding of the biology and ecology of particular species to help in the identification of effective treatment methods;
  8. Systems with strongly directional dispersion, such as invasive weeds with water-borne propagules in stream or river channels, are best tackled from the top of the watershed down, although downstream high-value sites at risk should be protected as well.
Invasive weed treatment strategies address the questions of "When?" and "Where?" weeds should be treated. Once this has been determined, the next question is "How?" Invasive weed treatments suppress these plants by changing the physical, chemical or biological state of the plants or their environment. Often the most effective treatment will include a combination of such effects. Treatments directly or indirectly affect the ability of the invasive weed to grow or reproduce.
Physical methods include mechanical removal, such as pulling by hand or with the use of tools such as the weed wrench, mowing, brush-cutting, tilling, excavation, controlled burning, and flaming. Chemical methods include the use of synthetic and organic herbicides. Biological methods includes the introduction of classical biocontrol agents, grazing by livestock, and revegetation. As an example of revegetation as a weed treatment method, shade intolerant species such as pampas grass can be suppressed by encouraging growth of the overstory. Biocontrol agents are considered a last resort. Their use indicates acceptance that the species is not eradicable, and the objective is to reduce the density of the weed population to an economically and environmentally-acceptable level.
Many weed treatment methods may be performed by the landowner, but a few, such as the application of certain herbicides, require the assistance of weed management professionals; these can be found in the Yellow Pages of your phone book. For advice on prescribed burns, consult your local CDF headquarters. Safety should always be of the highest priority in any weed treatment effort.
Weed scientists are conducting research on the biology and ecology of invasive weeds, continually providing new insight into more effective treatment strategies and methods for invasive weed management. Hyperlinks provided below allow you to connect to websites, such as the California Invasive Plant Council, that are devoted to providing up-to-date information on invasive weed treatment strategies and methods.

Exercises

  1. Considering the recommended priorities for allocating weed management resources, at what stage is weed management on your site? Have some priorities been overlooked?
  2. Using the hyperlinks provided below, research one particular weed species of interest to you. Address the priorities of the weed management strategy for this species.
    • How is it introduced and dispersed, and how can this be prevented?
    • Where would pioneer or satellite populations likely be found?
    • What methods could be used to remove them? Are these methods physical, chemical, biological or a combination?

References

 
The content of the page was last modified 2007-09-13