Weed Risk Assessment

Participants at the October 2006 WRA Workshop

Reprinted from Cal-IPC News, Winter 2007

We all know an ounce of prevention is worth a pound of cure, especially for weeds. But how can we know which new weeds to look out for? Which weeds already in California are most likely to expand into new areas? Which non-native plants might present a threat if introduced to California?

Such topics are the focus of the sub-discipline of Weed Risk Assessment (WRA). Cal-IPC’s Inventory uses a criteria system based on WRA principles to assess the severity of weeds already in the state. A new grant gives Cal-IPC the opportunity to begin work on answering more complex questions that will help weed workers’ ability to prevent weed spread and new introductions.

The grant, through Dr. Joe DiTomaso at UC Davis and the UC Integrated Pest Management Program (UC IPM), funds modeling of invasive plant distribution in California using climate and other factors. (See articles in Spring 2002 and Spring 2003 issues of Cal-IPC News for examples of predictive modeling.) Modeling will focus on 36 plants from our Inventory, choosing species that represent a range of severity and current distribution in California, as well as some chosen because they are sold as ornamentals.

To kick off the project, Cal-IPC organized the California WRA Workshop at the University of California-Davis on October 30-31, 2006, to discuss methods for predicting the spread of invasive plants in California. The invited participants included leading researchers from Australia, Hawaii, and Florida who have been at the forefront of developing tools to assess how severe a problem plants will become. The two-day meeting served to get Cal-IPC staff and others in the California weed community up to speed about what's being done here and abroad. (Special thanks to Rick Roush and the UC IPM program for sponsoring the meeting.)

The program covered three main areas—the science upon which WRA rests, the techniques used in WRA, and the policies for implementing WRA findings. For more information on the program and notes on discussions, please see the proceedings below.

At the end of the session, participants developed priorities for action. Because many entities worldwide are working on the same challenging issue, there is a great need to for sharing of information, both on specific plants and on effectiveness of predictive techniques. Hawaii and Florida have tested the Australian system that is used to screen all imports in that country, while USDA is revising our national screening protocol for horticultural introductions (Cal-IPC is submitting comment during their stakeholder input period). It is an important time to be engaged in this issue.

California Weed Risk Assessment Workshop Links

• Proceedings from the October 2006 Workshop at UC Davis (pdf)

Other Weed Risk Assessment Links

• 1^st International Weed Risk Assessment Workshop, Adelaide, Australia, 1999 - Papers presented at this meetings and a link to the book Weed Risk Assessment, produced as a Proceedings of the Workshop.
• 2^nd International Weed Risk Assessment Workshop, Perth, Australia, 2007 - A follow-up to the 1999 Workshop
• Pacific Islands Ecosystems at Risk - Risk assessments for invasive and potentially invasive plants in Hawaii and other Pacific islands. Adapted from the Biosecurity Australia system.
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