Invasive Weed Management

Prevention

Contents

Learning Objectives

[3] state the pathways of weed introduction and dispersal, and describe strategies to prevent it;

Narrative

Prevention is the first line of defense in integrated weed management.
"There are already at least 1,045 non-native plant species established in California (Randall et al.1998), and more continue to arrive and become established. If allowed to spread, some of these new species could impact native species and communities as severely as yellow starthistle and tamarisk do now. Preventing or stopping just one new invasive weed would be of greater conservation benefit in the long run than far more costly and difficult efforts to control an already widespread pest. " From Bossard, et al (2000).
For invasive weeds to be introduced into a site or dispersed within a site, there must be a source, a pathway and a destination. These three features together form a weed introduction or dispersal mechanism.
Sources are established invasive weed populations that are producing propagules (seeds or for some species, viable fragments.) Nearby invasive weed populations are always of concern, but the source may not be nearby if there is a pathway that can move these propagules across long distances to an invasible destination. Weed populations along trails and roads are particularly high risk because of the associated traffic (pathway), the disturbance associated with road construction and use (destination), and the greater availability of sunlight compared to shady forests and woodlands . Riaks from nearby populations are best reduced by cooperative action to manage invasive weeds. Risks from distant populations must be addressed through the pathway or the destination.
The high-risk pathways of introduction and dispersal may vary from one site to another. Consider the movement, artifical and otherwise, of humans, animals, vehicles, solid materials (gravel, fill, mulch, feed, straw, soil, seed mixes), water and wind on your site. If these pathways have the potential to move plant propagules from an invasive weed population into a weed-free area, there may be ways to minimize the risk. Reducing the frequency in the pathway, for instance by limiting access, is an effective approach but it may interfere with desirable land use. Risks may be mitigated by washing vehicles, equipment, boots and animals, confining animals who have been grazing in outside areas until their digestive systems have cleared, and selecting materials from weed-free sources.
Risk can also be reduced at the destination by taking actions to make the site less invasible (or preventing actions that make it more so.) Many invasive weeds prefer disturbed sites, some require full sunlight to thrive. Introduction may be prevented by minimizing disturbance, and revegetating after necessary disturbance. Select a mixture of revegetation species that will establish a healthy ecosystem that is resistant to invasion. It is wise to monitor those locations where disturbance has occured so that new infestations can be controlled before they are well-estabished.
Formal weed prevention plans have been developed in some areas to keep attention focused on prevention activities. It is easy to get distracted by other issues when there is not a large weed population in your face reminding you of the problem. The IMCWMA has developed a template Weed Prevention Area Plan for use by associations of rural land owners, such as road associations, based on a plan developed for the Williams Ranch Road Association (see references.)

Exercises

  1. For your site, consider each of the weed introduction and dispersal mechanisms mentioned in the narrative. Is this mechanism present on your site? Remember that source, pathway and destination must all be present. If you don't know, describe what you would need to do to find out.
  2. For a particular weed introduction mechanism, for example one identified in Exercise 1, state strategies for reducing risk at the source, the pathway and the destination. Which might be preferred and why?

References

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