Herbicide resistant weeds in California

Feb 17, 2017

Dear Weed Managers

Wednesday Feb. 15 of this week the Weed Science Society of America (WSSA) hosted a 4 hour listening session at the Tulare UCCE office conference room. In attendance were growers, consultants, ag industry personnel and university extension personnel. The WSSA is hosting 7 of these sessions around the US, the Tulare session was for the Southwestern US. The consensus was that people were aware of the difficulties that growers in the southeastern US were having with herbicide resistant weeds, but that outside of rice, herbicide resistant weeds in California are of concern but not a major problem. Worries about labor shortages, costs and regulations were of greater concern for California weed managers. 

My observation is that the ability to use a diverse set of tools including tillage has allowed people to manage weeds. Where people have gotten lax, such as in silage corn where junglerice has arisen, herbicide resistant weeds will develop here just like anywhere else. the difference is - corn can be cultivated and the junglerice can easily be controlled. I will not trivialize the situations where ground can not be tilled such as on erosion prone hillsides and roadsides (many others). The bottom line is herbicide resistant weeds are not a major constraint in California because people practice IPM.

However, we can not be complacent. There are few new herbicides on the horizon and where hand weeding is used now it must be replaced by other tools. We must look for weed control options outside of herbicides, some that involve tillage, and others that kill weeds by heat or abrasion. I have written about this elsewhere and will not repeat it here.

At the WSSA meeting last week in Tucson, Dr. Harry Strek of Bayer AG in Germany presented an integrated management plan used in Europe for weeds that included use of stale seedbed, herbicides and crop rotation. Dr. Strek told me they were very interested in weed removal automation and see it as a component in their future. This long-view collaboration between Ag chem industry, public researchers and automation engineers is an excellent model for a sustainable weed management that could be used indefinitely. We should do this in California. 

In closing I think we should focus on IPM and supplement our herbicides with physical and cultural tools where we can. IPM works and that is why herbicide resistant weeds are not a huge problem here.

Steve Fennimore


By Steven Fennimore
Author - CE Weed Specialist