Skip to Content
Weed control, management, ecology, and minutia
by Elizabeth Brusati
on May 31, 2017 at 3:49 PM
Thanks for trying to clarify these overlapping definitions, but I do not agree with your assertion that official noxious weeds are always “the worst of the worst” while the term invasive is simply a catch-all. State noxious weed lists generally focus on agricultural weeds and do not include many weeds of natural areas that are of serious concern to land managers. For example, the California Noxious Weed List does not include water hyacinth, even though CDFA’s fellow state agency, the Division of Boating and Waterways, has spent millions of dollars controlling it in the Delta. This gap exists because water hyacinth is also a popular ornamental plant and Section 2004 of the Food and Ag Code states that, “In determining whether or not a species shall be designated a noxious weed for the purposes of protecting silviculture or important native plant species, the director shall not make that designation if the designation will be detrimental to agriculture.” Growing ornamental plants is an important agricultural industry in California. Likewise, CDFA recently rejected ivy spp. for the Noxious Weed List even though its own evaluation states that, “These are very bad forest weeds” (  
Second, “invasive” can be applied rigorously as well. The California Invasive Plant Council’s Inventory, while non-regulatory, assesses plants invading natural areas using a 13 question criteria developed by Joe DiTomaso of UCD and others ( - as Chris M. knows, since he serves on the Inventory Review Committee!
by Chris McDonald
on June 1, 2017 at 10:50 AM
Elizabeth I appreciate your comments, they have helped me improve this blog. I provided minor edits to the blog to better streamline my thoughts. I deleted the sentence that noxious weeds are "the worst of the worst". I believe the designation noxious *should* apply to the worst of the worst and yet it sometimes doesn't always due to the loophole for agriculture as you pointed out. I didn't want to confuse the reader or stir up a conflict which is beyond my intention of clarifying definitions in this blog. I also clarified the section pointing the reader to FAC sec. 5004 which was pasted at the bottom of the original blog.  
The intention of this blog was to point out that these terms can be reasonably well defined and we can limit the amount of overlap between terms, and that it can also get messy when dealing with weeds because there is overlap (what to do with weeds that rank low on assessments, if we had C- or D+ rated weeds, they are still spreading, they might cause a little harm, they are also causing less harm then their bad brethren. I don't think we have a good answer to that, and hopefully using more concrete definitions will help us solve that issue)  
My intention was not to point out that these terms are vague, (they are loosely used, however!) and they should be applied rigorously. I hope that came across in the blog. My intention was not to be as specific as possible (i.e. "A noxious weed is defined more specifically than given in this post"), I wanted to give the reader a colloquial way to define weeds or possibly even a Venn diagram-type hierarchy to build definitions for weed, alien/exotic, pest, invasive, colonizer, transformer and noxious.
Leave a Reply:

You are currently not signed in. If you have an account, then sign in now!
Anonymous users messages may be delayed.

Security Code: