California Invasive Plant Council
The stewardship mandate of many land management organizations, such as park and open space districts, water districts, conservancies, and land trusts, requires addressing invasive plants that threaten biodiversity, fire safety, recreational experience, and other resource values. The Best Management Practices (BMPs) for non-chemical techniques available on this site are intended to assist land management organizations and weed workers in achieving this mandate.
Recent public concern about the risks of synthetic pesticides to humans and the environment have led to a renewed interest in decreasing pesticide use and incorporating non-chemical methods, where possible. Increasingly, governing bodies and organizations are considering how to reduce the use of herbicides in their invasive plant management practices. Some have excluded the use of synthetic herbicides entirely, which has eliminated what is generally considered the most effective suite of tools in the Integrated Pest Management (IPM) toolbox.
This Best Management Practices decision support tool was created collaboratively by the California Invasive Plant Council and the University of California’s Integrated Pest Management Program with funding from the California Department of Pesticide Regulation. The tool was created as a resource in response to these concerns and policy shifts. It provides guidance compiled from invasive plant management experts across California on selecting effective non-chemical control methods for different types of invasive plants and site conditions. We recommend that users employ the non-chemical methods described in this tool as one component in an integrated approach that also includes prevention, early detection, and the use of chemical approaches as needed.
The Best Management Practices (BMPs) provided with this decision support tool provide detailed descriptions of methods for land managers. However, decisions about land management practices are often made by governing boards and others without day-to-day, on-the-ground expertise in weed management. Public stakeholders need information to better understand and support these decisions about land management practices. The following points highlight several guiding principles in invasive plant management that are essential to understand when setting guidelines or policy about management practices.
Weed management needs steady attention with no breaks. Regardless of the specific technique used, land managers need the resources to address weeds every year so that targeted infestations cannot “go to seed”. Eliminating a weed infestation requires persistence to get any new plants that arise from the soil seed bank or vegetative propagules while not letting any new propagules be added to the soil.
Timing is everything. Many non-chemical methods are only effective for a very narrow period during plant development, whereas chemical techniques generally are effective for a broader seasonal window. For example, in order to be effective, both burning and grazing implemented to control invasive plants must occur after flower heads begin developing but before seeds have matured and dispersed to be effective. Other methods, such as manual removal with hand tools and flaming may require repeated visits to a site during the growing season to control additional weed seedling flushes and regrowth after initial treatment.
Scale is important. What works in a yard setting does not often translate well to a wildland setting because of the much greater scale of infestations. In addition, factors like slope, rockiness, and surrounding desirable vegetation come into play, and access to sites can be difficult.
Non-chemical methods are not necessarily safer. This goes for workers and the environment. Physical methods carry with them risk of injury to the worker, whether acute (like a chainsaw or vehicle accident) or chronic (like strain from repetitive motion). Heavy equipment and field crews can cause soil disturbance and erosion and digging impacts cultural resources. Mowing timed optimally to control weeds can harm nesting birds. Mechanized equipment, such as metal-bladed mowers, can create sparks that have potential to start fires. Grazing and fire may harm beneficial vegetation along with weeds. In short, any land management action can have potential undesirable impacts that need to be identified and minimized.
Different methods require different capacities. Training staff and volunteers on the use of hand tools is fairly straightforward. However, other non-chemical methods, such as grazing, burning, or use of heavy equipment, require specialized training and equipment or specialized contractors.
Non-chemical techniques have limitations.Some weed species in some situations may be virtually impossible to control without herbicides. This can be because of the plant’s reproductive abilities (like resprouting), the extent of the infestation, the budgetary limits of the organization, or other factors such as extensive environmental damage from physically removing plants and their reproductive structures (examples include Arundo and Japanese knotweed). Thus, a decision to not use herbicides at all means forgoing the possibility of controlling these weeds. Furthermore, the implementation of a non-chemical technique that can only partially control an invasive plant (e.g., by 60% annually) may not be sufficient to make up for its reproductive potential and can therefore be ineffective and costly over the long-term.
Non-chemical techniques can be expensive.Non-chemical techniques have been estimated to be five to eight times more expensive than chemical techniques to achieve the same level of control. Most of the increase in cost comes from the additional labor needed and the need for repeated visits to achieve control. Volunteer training and engagement is one very successful means by which to decrease cost and encourage effective land stewardship but will often not fill an increased labor need entirely or dependably.
This set of BMPs covers over 20 distinct non-chemical approaches to controlling weeds, including:
- A range of hand tools for cutting and digging
- Power tools, like saws and mowers
- Heavy equipment, like backhoes and bulldozers
- Ways to cover plants with tarps or mulch
- Ways to damage weeds with heat such as flaming or solarization
- Prescribed burning
- Grazing by cattle, sheep, or goats (each grazes differently)
- Biological control agents (for 19 distinct invasive plant species/species groups)
This extensive range of tools provides many options for stewardship organizations and can be used in different combinations to get the best results. It is important that the tools be integrated into a long-term management plan that is implemented consistently and adapted appropriately based on results. (The “Land Manager’s Guide to Developing an Invasive Plant Management Plan” developed by Cal-IPC in collaboration with the US Fish & Wildlife Service and other partners is a useful resource available for free download from the resource library on Cal-IPC’s website).
Governing boards and other decision-makers play a key role in structuring the land stewardship practices for organizations that care for public and private natural areas. This is a great opportunity—and responsibility—to make sure that land management for future generations is based on science, the best available information from practitioners, and input from community stakeholders.