Overview of AZ weed challenges

Nov. 16, 2021

The recent activity since winter 2019-20 has been around stinknet, Oncosiphon pilulifer, a very invasive winter annual weed in disturbed desert areas of AZ and also in CA. https://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1827-2020.pdf. It has been declared a noxious weed in AZ by the AZ Dept of Ag. The Southwest Vegetation Management Assn was influential in getting it listed a few years ago. The University of Arizona Cooperative Extension’s role has been mostly educational with Michael Chamberland’s bulletin describing the weed.  He has collaborated with UCCE to survey the weeds' spread.

I have conducted some postemergence weed control studies and posted research progress reports at:




I initiated a preemergence herbicide study last year but the drought allowed limited information on products efficacy.

Most municipalities and organizations have been trying to secure funding to control or prevent the weed invasions in public lands surrounding the metropolitan Phoenix area.

Another perennial weed, buffelgrass, has been spreading in the low desert southern part of AZ and moving northward. It is another extreme fire hazard in the desert and endangers the saguaro cactus and other vegetation that are not used to fire in the desert.  Another winter winter grass weed, red brome invades the low desert in the winter if rain is abundant. It too is an extreme fire hazard for the cactus and native vegetation. We are seeing more desert wildfires due to these weeds in AZ.

Much of AZ’s efforts against invasive weeds have been fragmented and individual groups and organizations try to tackle the weed problems in their own backyards.  Some cooperative weed management areas organize when its too late and laborious hand-pulling efforts are short-lived.  The SWVMA tries to organize statewide but is limited with few volunteers trying to organize a state effort.

AZ could take lessons and join other western organizations to try and get better organized to combat noxious and invasive weeds. Long term sustained efforts are needed.